This definition of the NFS version 4 protocol replaces or obsoletes
the definition present in [RFC3010]. While portions of the two
documents have remained the same, there have been substantive changes
in others. The changes made between [RFC3010] and this document
represent implementation experience and further review of the
protocol. While some modifications were made for ease of
implementation or clarification, most updates represent errors or
situations where the [RFC3010] definition were untenable.
The following list is not all inclusive of all changes but presents
some of the most notable changes or additions made:
o The state model has added an open_owner4 identifier. This was
done to accommodate Posix based clients and the model they use for
file locking. For Posix clients, an open_owner4 would correspond
to a file descriptor potentially shared amongst a set of processes
and the lock_owner4 identifier would correspond to a process that
is locking a file.
o Clarifications and error conditions were added for the handling of
the owner and group attributes. Since these attributes are string
based (as opposed to the numeric uid/gid of previous versions of
NFS), translations may not be available and hence the changes
made.
o Clarifications for the ACL and mode attributes to address
evaluation and partial support.
o For identifiers that are defined as XDR opaque, limits were set on
their size.
o Added the mounted_on_filed attribute to allow Posix clients to
correctly construct local mounts.
o Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
correctly with confirmation details along with adding the ability
to specify new client callback information. Also added
clarification of the callback information itself.
o Added a new operation LOCKOWNER_RELEASE to enable notifying the
server that a lock_owner4 will no longer be used by the client.
o RENEW operation changes to identify the client correctly and allow
for additional error returns.
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o Verify error return possibilities for all operations.
o Remove use of the pathname4 data type from LOOKUP and OPEN in
favor of having the client construct a sequence of LOOKUP
operations to achieive the same effect.
o Clarification of the internationalization issues and adoption of
the new stringprep profile framework.
The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions 2 [RFC1094] and 3 [RFC1813]. It retains
the essential characteristics of previous versions: design for easy
recovery, independent of transport protocols, operating systems and
filesystems, simplicity, and good performance. The NFS version 4
revision has the following goals:
o Improved access and good performance on the Internet.
The protocol is designed to transit firewalls easily, perform well
where latency is high and bandwidth is low, and scale to very
large numbers of clients per server.
o Strong security with negotiation built into the protocol.
The protocol builds on the work of the ONCRPC working group in
supporting the RPCSEC_GSS protocol. Additionally, the NFS version
4 protocol provides a mechanism to allow clients and servers the
ability to negotiate security and require clients and servers to
support a minimal set of security schemes.
o Good cross-platform interoperability.
The protocol features a filesystem model that provides a useful,
common set of features that does not unduly favor one filesystem
or operating system over another.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions that do not
compromise backward compatibility.
Section 18, RPC Definition File, contains the definitions in XDR
description language of the constructs used by the protocol. Prior
to Section 18, several of the constructs are reproduced for purposes
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of explanation. The reader is warned of the possibility of errors in
the reproduced constructs outside of Section 18. For any part of the
document that is inconsistent with Section 18, Section 18 is to be
considered authoritative.
To provide a reasonable context for the reader, the major features of
NFS version 4 protocol will be reviewed in brief. This will be done
to provide an appropriate context for both the reader who is familiar
with the previous versions of the NFS protocol and the reader that is
new to the NFS protocols. For the reader new to the NFS protocols,
there is still a fundamental knowledge that is expected. The reader
should be familiar with the XDR and RPC protocols as described in
[RFC1831] and [RFC1832]. A basic knowledge of filesystems and
distributed filesystems is expected as well.
As with previous versions of NFS, the External Data Representation
(XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
version 4 protocol are those defined in [RFC1831] and [RFC1832]. To
meet end to end security requirements, the RPCSEC_GSS framework
[RFC2203] will be used to extend the basic RPC security. With the
use of RPCSEC_GSS, various mechanisms can be provided to offer
authentication, integrity, and privacy to the NFS version 4 protocol.
Kerberos V5 will be used as described in [RFC1964] to provide one
security framework. The LIPKEY GSS-API mechanism described in
[RFC2847] will be used to provide for the use of user password and
server public key by the NFS version 4 protocol. With the use of
RPCSEC_GSS, other mechanisms may also be specified and used for NFS
version 4 security.
To enable in-band security negotiation, the NFS version 4 protocol
has added a new operation which provides the client a method of
querying the server about its policies regarding which security
mechanisms must be used for access to the server's filesystem
resources. With this, the client can securely match the security
mechanism that meets the policies specified at both the client and
server.
A significant departure from the previous versions of the NFS
protocol is the introduction of the COMPOUND procedure. For the NFS
version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
The COMPOUND procedure is defined in terms of operations and these
operations correspond more closely to the traditional NFS procedures.
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With the use of the COMPOUND procedure, the client is able to build
simple or complex requests. These COMPOUND requests allow for a
reduction in the number of RPCs needed for logical filesystem
operations. For example, without previous contact with a server a
client will be able to read data from a file in one request by
combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
With previous versions of the NFS protocol, this type of single
request was not possible.
The model used for COMPOUND is very simple. There is no logical OR
or ANDing of operations. The operations combined within a COMPOUND
request are evaluated in order by the server. Once an operation
returns a failing result, the evaluation ends and the results of all
evaluated operations are returned to the client.
The NFS version 4 protocol continues to have the client refer to a
file or directory at the server by a "filehandle". The COMPOUND
procedure has a method of passing a filehandle from one operation to
another within the sequence of operations. There is a concept of a
"current filehandle" and "saved filehandle". Most operations use the
"current filehandle" as the filesystem object to operate upon. The
"saved filehandle" is used as temporary filehandle storage within a
COMPOUND procedure as well as an additional operand for certain
operations.
The general filesystem model used for the NFS version 4 protocol is
the same as previous versions. The server filesystem is hierarchical
with the regular files contained within being treated as opaque byte
streams. In a slight departure, file and directory names are encoded
with UTF-8 to deal with the basics of internationalization.
The NFS version 4 protocol does not require a separate protocol to
provide for the initial mapping between path name and filehandle.
Instead of using the older MOUNT protocol for this mapping, the
server provides a ROOT filehandle that represents the logical root or
top of the filesystem tree provided by the server. The server
provides multiple filesystems by gluing them together with pseudo
filesystems. These pseudo filesystems provide for potential gaps in
the path names between real filesystems.
In previous versions of the NFS protocol, the filehandle provided by
the server was guaranteed to be valid or persistent for the lifetime
of the filesystem object to which it referred. For some server
implementations, this persistence requirement has been difficult to
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meet. For the NFS version 4 protocol, this requirement has been
relaxed by introducing another type of filehandle, volatile. With
persistent and volatile filehandle types, the server implementation
can match the abilities of the filesystem at the server along with
the operating environment. The client will have knowledge of the
type of filehandle being provided by the server and can be prepared
to deal with the semantics of each.
The NFS version 4 protocol introduces three classes of filesystem or
file attributes. Like the additional filehandle type, the
classification of file attributes has been done to ease server
implementations along with extending the overall functionality of the
NFS protocol. This attribute model is structured to be extensible
such that new attributes can be introduced in minor revisions of the
protocol without requiring significant rework.
The three classifications are: mandatory, recommended and named
attributes. This is a significant departure from the previous
attribute model used in the NFS protocol. Previously, the attributes
for the filesystem and file objects were a fixed set of mainly UNIX
attributes. If the server or client did not support a particular
attribute, it would have to simulate the attribute the best it could.
Mandatory attributes are the minimal set of file or filesystem
attributes that must be provided by the server and must be properly
represented by the server. Recommended attributes represent
different filesystem types and operating environments. The
recommended attributes will allow for better interoperability and the
inclusion of more operating environments. The mandatory and
recommended attribute sets are traditional file or filesystem
attributes. The third type of attribute is the named attribute. A
named attribute is an opaque byte stream that is associated with a
directory or file and referred to by a string name. Named attributes
are meant to be used by client applications as a method to associate
application specific data with a regular file or directory.
One significant addition to the recommended set of file attributes is
the Access Control List (ACL) attribute. This attribute provides for
directory and file access control beyond the model used in previous
versions of the NFS protocol. The ACL definition allows for
specification of user and group level access control.
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With the use of a special file attribute, the ability to migrate or
replicate server filesystems is enabled within the protocol. The
filesystem locations attribute provides a method for the client to
probe the server about the location of a filesystem. In the event of
a migration of a filesystem, the client will receive an error when
operating on the filesystem and it can then query as to the new file
system location. Similar steps are used for replication, the client
is able to query the server for the multiple available locations of a
particular filesystem. From this information, the client can use its
own policies to access the appropriate filesystem location.
The NFS version 4 protocol introduces OPEN and CLOSE operations. The
OPEN operation provides a single point where file lookup, creation,
and share semantics can be combined. The CLOSE operation also
provides for the release of state accumulated by OPEN.
With the NFS version 4 protocol, the support for byte range file
locking is part of the NFS protocol. The file locking support is
structured so that an RPC callback mechanism is not required. This
is a departure from the previous versions of the NFS file locking
protocol, Network Lock Manager (NLM). The state associated with file
locks is maintained at the server under a lease-based model. The
server defines a single lease period for all state held by a NFS
client. If the client does not renew its lease within the defined
period, all state associated with the client's lease may be released
by the server. The client may renew its lease with use of the RENEW
operation or implicitly by use of other operations (primarily READ).
The file, attribute, and directory caching for the NFS version 4
protocol is similar to previous versions. Attributes and directory
information are cached for a duration determined by the client. At
the end of a predefined timeout, the client will query the server to
see if the related filesystem object has been updated.
For file data, the client checks its cache validity when the file is
opened. A query is sent to the server to determine if the file has
been changed. Based on this information, the client determines if
the data cache for the file should kept or released. Also, when the
file is closed, any modified data is written to the server.
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If an application wants to serialize access to file data, file
locking of the file data ranges in question should be used.
The major addition to NFS version 4 in the area of caching is the
ability of the server to delegate certain responsibilities to the
client. When the server grants a delegation for a file to a client,
the client is guaranteed certain semantics with respect to the
sharing of that file with other clients. At OPEN, the server may
provide the client either a read or write delegation for the file.
If the client is granted a read delegation, it is assured that no
other client has the ability to write to the file for the duration of
the delegation. If the client is granted a write delegation, the
client is assured that no other client has read or write access to
the file.
Delegations can be recalled by the server. If another client
requests access to the file in such a way that the access conflicts
with the granted delegation, the server is able to notify the initial
client and recall the delegation. This requires that a callback path
exist between the server and client. If this callback path does not
exist, then delegations can not be granted. The essence of a
delegation is that it allows the client to locally service operations
such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
interaction with the server.
The following definitions are provided for the purpose of providing
an appropriate context for the reader.
Client The "client" is the entity that accesses the NFS server's
resources. The client may be an application which contains
the logic to access the NFS server directly. The client
may also be the traditional operating system client remote
filesystem services for a set of applications.
In the case of file locking the client is the entity that
maintains a set of locks on behalf of one or more
applications. This client is responsible for crash or
failure recovery for those locks it manages.
Note that multiple clients may share the same transport and
multiple clients may exist on the same network node.
Clientid A 64-bit quantity used as a unique, short-hand reference to
a client supplied Verifier and ID. The server is
responsible for supplying the Clientid.
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Lease An interval of time defined by the server for which the
client is irrevocably granted a lock. At the end of a
lease period the lock may be revoked if the lease has not
been extended. The lock must be revoked if a conflicting
lock has been granted after the lease interval.
All leases granted by a server have the same fixed
interval. Note that the fixed interval was chosen to
alleviate the expense a server would have in maintaining
state about variable length leases across server failures.
Lock The term "lock" is used to refer to both record (byte-
range) locks as well as share reservations unless
specifically stated otherwise.
Server The "Server" is the entity responsible for coordinating
client access to a set of filesystems.
Stable Storage
NFS version 4 servers must be able to recover without data
loss from multiple power failures (including cascading
power failures, that is, several power failures in quick
succession), operating system failures, and hardware
failure of components other than the storage medium itself
(for example, disk, nonvolatile RAM).
Some examples of stable storage that are allowable for an
NFS server include:
1. Media commit of data, that is, the modified data has
been successfully written to the disk media, for
example, the disk platter.
2. An immediate reply disk drive with battery-backed on-
drive intermediate storage or uninterruptible power
system (UPS).
3. Server commit of data with battery-backed intermediate
storage and recovery software.
4. Cache commit with uninterruptible power system (UPS) and
recovery software.
Stateid A 128-bit quantity returned by a server that uniquely
defines the open and locking state provided by the server
for a specific open or lock owner for a specific file.
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Stateids composed of all bits 0 or all bits 1 have special
meaning and are reserved values.
Verifier A 64-bit quantity generated by the client that the server
can use to determine if the client has restarted and lost
all previous lock state.
The syntax and semantics to describe the data types of the NFS
version 4 protocol are defined in the XDR [RFC1832] and RPC [RFC1831]
documents. The next sections build upon the XDR data types to define
types and structures specific to this protocol.
Data Type Definition
____________________________________________________________________
int32_t typedef int int32_t;
uint32_t typedef unsigned int uint32_t;
int64_t typedef hyper int64_t;
uint64_t typedef unsigned hyper uint64_t;
attrlist4 typedef opaque attrlist4<>;
Used for file/directory attributes
bitmap4 typedef uint32_t bitmap4<>;
Used in attribute array encoding.
changeid4 typedef uint64_t changeid4;
Used in definition of change_info
clientid4 typedef uint64_t clientid4;
Shorthand reference to client identification
component4 typedef utf8str_cs component4;
Represents path name components
count4 typedef uint32_t count4;
Various count parameters (READ, WRITE, COMMIT)
length4 typedef uint64_t length4;
Describes LOCK lengths
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linktext4 typedef utf8str_cs linktext4;
Symbolic link contents
mode4 typedef uint32_t mode4;
Mode attribute data type
nfs_cookie4 typedef uint64_t nfs_cookie4;
Opaque cookie value for READDIR
nfs_fh4 typedef opaque nfs_fh4<NFS4_FHSIZE>;
Filehandle definition; NFS4_FHSIZE is defined as 128
nfs_ftype4 enum nfs_ftype4;
Various defined file types
nfsstat4 enum nfsstat4;
Return value for operations
offset4 typedef uint64_t offset4;
Various offset designations (READ, WRITE,
LOCK, COMMIT)
pathname4 typedef component4 pathname4<>;
Represents path name for LOOKUP, OPEN and others
qop4 typedef uint32_t qop4;
Quality of protection designation in SECINFO
sec_oid4 typedef opaque sec_oid4<>;
Security Object Identifier
The sec_oid4 data type is not really opaque.
Instead contains an ASN.1 OBJECT IDENTIFIER as used
by GSS-API in the mech_type argument to
GSS_Init_sec_context. See [RFC2743] for details.
seqid4 typedef uint32_t seqid4;
Sequence identifier used for file locking
utf8string typedef opaque utf8string<>;
UTF-8 encoding for strings
utf8str_cis typedef opaque utf8str_cis;
Case-insensitive UTF-8 string
utf8str_cs typedef opaque utf8str_cs;
Case-sensitive UTF-8 string
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utf8str_mixed typedef opaque utf8str_mixed;
UTF-8 strings with a case sensitive prefix and
a case insensitive suffix.
verifier4 typedef opaque verifier4[NFS4_VERIFIER_SIZE];
Verifier used for various operations (COMMIT,
CREATE, OPEN, READDIR, SETCLIENTID,
SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is
defined as 8.
nfstime4
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
}
The nfstime4 structure gives the number of seconds and nanoseconds
since midnight or 0 hour January 1, 1970 Coordinated Universal Time
(UTC). Values greater than zero for the seconds field denote dates
after the 0 hour January 1, 1970. Values less than zero for the
seconds field denote dates before the 0 hour January 1, 1970. In
both cases, the nseconds field is to be added to the seconds field
for the final time representation. For example, if the time to be
represented is one-half second before 0 hour January 1, 1970, the
seconds field would have a value of negative one (-1) and the
nseconds fields would have a value of one-half second (500000000).
Values greater than 999,999,999 for nseconds are considered invalid.
This data type is used to pass time and date information. A server
converts to and from its local representation of time when processing
time values, preserving as much accuracy as possible. If the
precision of timestamps stored for a filesystem object is less than
defined, loss of precision can occur. An adjunct time maintenance
protocol is recommended to reduce client and server time skew.
time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
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RFC 3530 NFS version 4 Protocol April 2003
settime4
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
The above definitions are used as the attribute definitions to set
time values. If set_it is SET_TO_SERVER_TIME4, then the server uses
its local representation of time for the time value.
specdata4
struct specdata4 {
uint32_t specdata1; /* major device number */
uint32_t specdata2; /* minor device number */
};
This data type represents additional information for the device file
types NF4CHR and NF4BLK.
fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
This type is the filesystem identifier that is used as a mandatory
attribute.
fs_location4
struct fs_location4 {
utf8str_cis server<>;
pathname4 rootpath;
};
fs_locations4
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
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The fs_location4 and fs_locations4 data types are used for the
fs_locations recommended attribute which is used for migration and
replication support.
fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
attributes.
The bitmap is a counted array of 32 bit integers used to contain bit
values. The position of the integer in the array that contains bit n
can be computed from the expression (n / 32) and its bit within that
integer is (n mod 32).
0 1
+-----------+-----------+-----------+--
| count | 31 .. 0 | 63 .. 32 |
+-----------+-----------+-----------+--
change_info4
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This structure is used with the CREATE, LINK, REMOVE, RENAME
operations to let the client know the value of the change attribute
for the directory in which the target filesystem object resides.
clientaddr4
struct clientaddr4 {
/* see struct rpcb in RFC 1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
The clientaddr4 structure is used as part of the SETCLIENTID
operation to either specify the address of the client that is using a
clientid or as part of the callback registration. The
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r_netid and r_addr fields are specified in [RFC1833], but they are
underspecified in [RFC1833] as far as what they should look like for
specific protocols.
For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
US-ASCII string:
h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for
representing an IPv4 address, which is always four octets long.
Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
the first through fourth octets each converted to ASCII-decimal.
Assuming big-endian ordering, p1 and p2 are, respectively, the first
and second octets each converted to ASCII-decimal. For example, if a
host, in big-endian order, has an address of 0x0A010307 and there is
a service listening on, in big endian order, port 0x020F (decimal
527), then the complete universal address is "10.1.3.7.2.15".
For TCP over IPv4 the value of r_netid is the string "tcp". For UDP
over IPv4 the value of r_netid is the string "udp".
For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
US-ASCII string:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
The suffix "p1.p2" is the service port, and is computed the same way
as with universal addresses for TCP and UDP over IPv4. The prefix,
"x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
representing an IPv6 address as defined in Section 2.2 of [RFC2373].
Additionally, the two alternative forms specified in Section 2.2 of
[RFC2373] are also acceptable.
For TCP over IPv6 the value of r_netid is the string "tcp6". For UDP
over IPv6 the value of r_netid is the string "udp6".
cb_client4
struct cb_client4 {
unsigned int cb_program;
clientaddr4 cb_location;
};
This structure is used by the client to inform the server of its call
back address; includes the program number and client address.
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nfs_client_id4
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
This structure is part of the arguments to the SETCLIENTID operation.
NFS4_OPAQUE_LIMIT is defined as 1024.
open_owner4
struct open_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of open state.
NFS4_OPAQUE_LIMIT is defined as 1024.
lock_owner4
struct lock_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of file locking state.
NFS4_OPAQUE_LIMIT is defined as 1024.
open_to_lock_owner4
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This structure is used for the first LOCK operation done for an
open_owner4. It provides both the open_stateid and lock_owner such
that the transition is made from a valid open_stateid sequence to
that of the new lock_stateid sequence. Using this mechanism avoids
the confirmation of the lock_owner/lock_seqid pair since it is tied
to established state in the form of the open_stateid/open_seqid.
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RFC 3530 NFS version 4 Protocol April 2003
stateid4
struct stateid4 {
uint32_t seqid;
opaque other[12];
};
This structure is used for the various state sharing mechanisms
between the client and server. For the client, this data structure
is read-only. The starting value of the seqid field is undefined.
The server is required to increment the seqid field monotonically at
each transition of the stateid. This is important since the client
will inspect the seqid in OPEN stateids to determine the order of
OPEN processing done by the server.
The NFS version 4 protocol is a Remote Procedure Call (RPC)
application that uses RPC version 2 and the corresponding eXternal
Data Representation (XDR) as defined in [RFC1831] and [RFC1832]. The
RPCSEC_GSS security flavor as defined in [RFC2203] MUST be used as
the mechanism to deliver stronger security for the NFS version 4
protocol.
Historically, NFS version 2 and version 3 servers have resided on
port 2049. The registered port 2049 [RFC3232] for the NFS protocol
should be the default configuration. Using the registered port for
NFS services means the NFS client will not need to use the RPC
binding protocols as described in [RFC1833]; this will allow NFS to
transit firewalls.
Where an NFS version 4 implementation supports operation over the IP
network protocol, the supported transports between NFS and IP MUST be
among the IETF-approved congestion control transport protocols, which
include TCP and SCTP. To enhance the possibilities for
interoperability, an NFS version 4 implementation MUST support
operation over the TCP transport protocol, at least until such time
as a standards track RFC revises this requirement to use a different
IETF-approved congestion control transport protocol.
If TCP is used as the transport, the client and server SHOULD use
persistent connections. This will prevent the weakening of TCP's
congestion control via short lived connections and will improve
performance for the WAN environment by eliminating the need for SYN
handshakes.
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RFC 3530 NFS version 4 Protocol April 2003
As noted in the Security Considerations section, the authentication
model for NFS version 4 has moved from machine-based to principal-
based. However, this modification of the authentication model does
not imply a technical requirement to move the TCP connection
management model from whole machine-based to one based on a per user
model. In particular, NFS over TCP client implementations have
traditionally multiplexed traffic for multiple users over a common
TCP connection between an NFS client and server. This has been true,
regardless whether the NFS client is using AUTH_SYS, AUTH_DH,
RPCSEC_GSS or any other flavor. Similarly, NFS over TCP server
implementations have assumed such a model and thus scale the
implementation of TCP connection management in proportion to the
number of expected client machines. It is intended that NFS version
4 will not modify this connection management model. NFS version 4
clients that violate this assumption can expect scaling issues on the
server and hence reduced service.
Note that for various timers, the client and server should avoid
inadvertent synchronization of those timers. For further discussion
of the general issue refer to [Floyd].
When processing a request received over a reliable transport such as
TCP, the NFS version 4 server MUST NOT silently drop the request,
except if the transport connection has been broken. Given such a
contract between NFS version 4 clients and servers, clients MUST NOT
retry a request unless one or both of the following are true:
o The transport connection has been broken
o The procedure being retried is the NULL procedure
Since reliable transports, such as TCP, do not always synchronously
inform a peer when the other peer has broken the connection (for
example, when an NFS server reboots), the NFS version 4 client may
want to actively "probe" the connection to see if has been broken.
Use of the NULL procedure is one recommended way to do so. So, when
a client experiences a remote procedure call timeout (of some
arbitrary implementation specific amount), rather than retrying the
remote procedure call, it could instead issue a NULL procedure call
to the server. If the server has died, the transport connection
break will eventually be indicated to the NFS version 4 client. The
client can then reconnect, and then retry the original request. If
the NULL procedure call gets a response, the connection has not
broken. The client can decide to wait longer for the original
request's response, or it can break the transport connection and
reconnect before re-sending the original request.
Shepler, et al. Standards Track [Page 24]
RFC 3530 NFS version 4 Protocol April 2003
For callbacks from the server to the client, the same rules apply,
but the server doing the callback becomes the client, and the client
receiving the callback becomes the server.
Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
AUTH_DH, and AUTH_KRB4 as security flavors. With [RFC2203] an
additional security flavor of RPCSEC_GSS has been introduced which
uses the functionality of GSS-API [RFC2743]. This allows for the use
of various security mechanisms by the RPC layer without the
additional implementation overhead of adding RPC security flavors.
For NFS version 4, the RPCSEC_GSS security flavor MUST be used to
enable the mandatory security mechanism. Other flavors, such as,
AUTH_NONE, AUTH_SYS, and AUTH_DH MAY be implemented as well.
The use of RPCSEC_GSS requires selection of: mechanism, quality of
protection, and service (authentication, integrity, privacy). The
remainder of this document will refer to these three parameters of
the RPCSEC_GSS security as the security triple.
The Kerberos V5 GSS-API mechanism as described in [RFC1964] MUST be
implemented and provide the following security triples.
column descriptions:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == mechanism's algorithm(s)
5 == RPCSEC_GSS service
1 2 3 4 5
--------------------------------------------------------------------
390003 krb5 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_none
390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_integrity
390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_privacy
for integrity,
and 56 bit DES
for privacy.
Note that the pseudo flavor is presented here as a mapping aid to the
implementor. Because this NFS protocol includes a method to
negotiate security and it understands the GSS-API mechanism, the
Shepler, et al. Standards Track [Page 25]
RFC 3530 NFS version 4 Protocol April 2003
pseudo flavor is not needed. The pseudo flavor is needed for NFS
version 3 since the security negotiation is done via the MOUNT
protocol.
For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
see [RFC2623].
Users and implementors are warned that 56 bit DES is no longer
considered state of the art in terms of resistance to brute force
attacks. Once a revision to [RFC1964] is available that adds support
for AES, implementors are urged to incorporate AES into their NFSv4
over Kerberos V5 protocol stacks, and users are similarly urged to
migrate to the use of AES.
The LIPKEY GSS-API mechanism as described in [RFC2847] MUST be
implemented and provide the following security triples. The
definition of the columns matches the previous subsection "Kerberos
V5 as security triple"
1 2 3 4 5
--------------------------------------------------------------------
390006 lipkey 1.3.6.1.5.5.9 negotiated rpc_gss_svc_none
390007 lipkey-i 1.3.6.1.5.5.9 negotiated rpc_gss_svc_integrity
390008 lipkey-p 1.3.6.1.5.5.9 negotiated rpc_gss_svc_privacy
The mechanism algorithm is listed as "negotiated". This is because
LIPKEY is layered on SPKM-3 and in SPKM-3 [RFC2847] the
confidentiality and integrity algorithms are negotiated. Since
SPKM-3 specifies HMAC-MD5 for integrity as MANDATORY, 128 bit
cast5CBC for confidentiality for privacy as MANDATORY, and further
specifies that HMAC-MD5 and cast5CBC MUST be listed first before
weaker algorithms, specifying "negotiated" in column 4 does not
impair interoperability. In the event an SPKM-3 peer does not
support the mandatory algorithms, the other peer is free to accept or
reject the GSS-API context creation.
Because SPKM-3 negotiates the algorithms, subsequent calls to
LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
of protection value of 0 (zero). See section 5.2 of [RFC2025] for an
explanation.
LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
name and password from the client to the server. Once the user name
and password have been accepted by the server, calls to the LIPKEY
context are redirected to the SPKM-3 context. See [RFC2847] for more
details.
Shepler, et al. Standards Track [Page 26]
RFC 3530 NFS version 4 Protocol April 2003
The SPKM-3 GSS-API mechanism as described in [RFC2847] MUST be
implemented and provide the following security triples. The
definition of the columns matches the previous subsection "Kerberos
V5 as security triple".
1 2 3 4 5
--------------------------------------------------------------------
390009 spkm3 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_none
390010 spkm3i 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_integrity
390011 spkm3p 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_privacy
For a discussion as to why the mechanism algorithm is listed as
"negotiated", see the previous section "LIPKEY as a security triple."
Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
protection value of 0 (zero). See section 5.2 of [RFC2025] for an
explanation.
Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
mandatory set of triples to handle the situations where the initiator
(the client) is anonymous or where the initiator has its own
certificate. If the initiator is anonymous, there will not be a user
name and password to send to the target (the server). If the
initiator has its own certificate, then using passwords is
superfluous.
With the NFS version 4 server potentially offering multiple security
mechanisms, the client needs a method to determine or negotiate which
mechanism is to be used for its communication with the server. The
NFS server may have multiple points within its filesystem name space
that are available for use by NFS clients. In turn the NFS server
may be configured such that each of these entry points may have
different or multiple security mechanisms in use.
The security negotiation between client and server must be done with
a secure channel to eliminate the possibility of a third party
intercepting the negotiation sequence and forcing the client and
server to choose a lower level of security than required or desired.
See the section "Security Considerations" for further discussion.
Shepler, et al. Standards Track [Page 27]
RFC 3530 NFS version 4 Protocol April 2003
The new SECINFO operation will allow the client to determine, on a
per filehandle basis, what security triple is to be used for server
access. In general, the client will not have to use the SECINFO
operation except during initial communication with the server or when
the client crosses policy boundaries at the server. It is possible
that the server's policies change during the client's interaction
therefore forcing the client to negotiate a new security triple.
Based on the assumption that each NFS version 4 client and server
must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
communication with the server with one of the minimal security
triples. During communication with the server, the client may
receive an NFS error of NFS4ERR_WRONGSEC. This error allows the
server to notify the client that the security triple currently being
used is not appropriate for access to the server's filesystem
resources. The client is then responsible for determining what
security triples are available at the server and choose one which is
appropriate for the client. See the section for the "SECINFO"
operation for further discussion of how the client will respond to
the NFS4ERR_WRONGSEC error and use SECINFO.
Except as noted elsewhere in this section, the callback RPC
(described later) MUST mutually authenticate the NFS server to the
principal that acquired the clientid (also described later), using
the security flavor the original SETCLIENTID operation used.
For AUTH_NONE, there are no principals, so this is a non-issue.
AUTH_SYS has no notions of mutual authentication or a server
principal, so the callback from the server simply uses the AUTH_SYS
credential that the user used when he set up the delegation.
For AUTH_DH, one commonly used convention is that the server uses the
credential corresponding to this AUTH_DH principal:
unix.host@domain
where host and domain are variables corresponding to the name of
server host and directory services domain in which it lives such as a
Network Information System domain or a DNS domain.
Shepler, et al. Standards Track [Page 28]
RFC 3530 NFS version 4 Protocol April 2003
Because LIPKEY is layered over SPKM-3, it is permissible for the
server to use SPKM-3 and not LIPKEY for the callback even if the
client used LIPKEY for SETCLIENTID.
Regardless of what security mechanism under RPCSEC_GSS is being used,
the NFS server, MUST identify itself in GSS-API via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE
names are of the form:
service@hostname
For NFS, the "service" element is
nfs
Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5 and LIPKEY, the following
form is RECOMMENDED:
nfs/hostname
For Kerberos V5, nfs/hostname would be a server principal in the
Kerberos Key Distribution Center database. This is the same
principal the client acquired a GSS-API context for when it issued
the SETCLIENTID operation, therefore, the realm name for the server
principal must be the same for the callback as it was for the
SETCLIENTID.
For LIPKEY, this would be the username passed to the target (the NFS
version 4 client that receives the callback).
It should be noted that LIPKEY may not work for callbacks, since the
LIPKEY client uses a user id/password. If the NFS client receiving
the callback can authenticate the NFS server's user name/password
pair, and if the user that the NFS server is authenticating to has a
public key certificate, then it works.
In situations where the NFS client uses LIPKEY and uses a per-host
principal for the SETCLIENTID operation, instead of using LIPKEY for
SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
be used. This effectively means that the client will use a
certificate to authenticate and identify the initiator to the target
on the NFS server. Using SPKM-3 and not LIPKEY has the following
advantages:
o When the server does a callback, it must authenticate to the
principal used in the SETCLIENTID. Even if LIPKEY is used,
because LIPKEY is layered over SPKM-3, the NFS client will need to
Shepler, et al. Standards Track [Page 29]
RFC 3530 NFS version 4 Protocol April 2003
have a certificate that corresponds to the principal used in the
SETCLIENTID operation. From an administrative perspective, having
a user name, password, and certificate for both the client and
server is redundant.
o LIPKEY was intended to minimize additional infrastructure
requirements beyond a certificate for the target, and the
expectation is that existing password infrastructure can be
leveraged for the initiator. In some environments, a per-host
password does not exist yet. If certificates are used for any
per-host principals, then additional password infrastructure is
not needed.
o In cases when a host is both an NFS client and server, it can
share the same per-host certificate.
The filehandle in the NFS protocol is a per server unique identifier
for a filesystem object. The contents of the filehandle are opaque
to the client. Therefore, the server is responsible for translating
the filehandle to an internal representation of the filesystem
object.
The operations of the NFS protocol are defined in terms of one or
more filehandles. Therefore, the client needs a filehandle to
initiate communication with the server. With the NFS version 2
protocol [RFC1094] and the NFS version 3 protocol [RFC1813], there
exists an ancillary protocol to obtain this first filehandle. The
MOUNT protocol, RPC program number 100005, provides the mechanism of
translating a string based filesystem path name to a filehandle which
can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use
via firewalls. This is one reason that the use of the public
filehandle was introduced in [RFC2054] and [RFC2055]. With the use
of the public filehandle in combination with the LOOKUP operation in
the NFS version 2 and 3 protocols, it has been demonstrated that the
MOUNT protocol is unnecessary for viable interaction between NFS
client and server.
Therefore, the NFS version 4 protocol will not use an ancillary
protocol for translation from string based path names to a
filehandle. Two special filehandles will be used as starting points
for the NFS client.
Shepler, et al. Standards Track [Page 30]
RFC 3530 NFS version 4 Protocol April 2003
The first of the special filehandles is the ROOT filehandle. The
ROOT filehandle is the "conceptual" root of the filesystem name space
at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
operation instructs the server to set the "current" filehandle to the
ROOT of the server's file tree. Once this PUTROOTFH operation is
used, the client can then traverse the entirety of the server's file
tree with the LOOKUP operation. A complete discussion of the server
name space is in the section "NFS Server Name Space".
The second special filehandle is the PUBLIC filehandle. Unlike the
ROOT filehandle, the PUBLIC filehandle may be bound or represent an
arbitrary filesystem object at the server. The server is responsible
for this binding. It may be that the PUBLIC filehandle and the ROOT
filehandle refer to the same filesystem object. However, it is up to
the administrative software at the server and the policies of the
server administrator to define the binding of the PUBLIC filehandle
and server filesystem object. The client may not make any
assumptions about this binding. The client uses the PUBLIC
filehandle via the PUTPUBFH operation.
In the NFS version 2 and 3 protocols, there was one type of
filehandle with a single set of semantics. This type of filehandle
is termed "persistent" in NFS Version 4. The semantics of a
persistent filehandle remain the same as before. A new type of
filehandle introduced in NFS Version 4 is the "volatile" filehandle,
which attempts to accommodate certain server environments.
The volatile filehandle type was introduced to address server
functionality or implementation issues which make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a filesystem level invariant that can be
used to construct a persistent filehandle. The underlying server
filesystem may not provide the invariant or the server's filesystem
programming interfaces may not provide access to the needed
invariant. Volatile filehandles may ease the implementation of
server functionality such as hierarchical storage management or
filesystem reorganization or migration. However, the volatile
filehandle increases the implementation burden for the client.
Shepler, et al. Standards Track [Page 31]
RFC 3530 NFS version 4 Protocol April 2003
Since the client will need to handle persistent and volatile
filehandles differently, a file attribute is defined which may be
used by the client to determine the filehandle types being returned
by the server.
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality by
doing a byte-by-byte comparison. However, the client MUST NOT
otherwise interpret the contents of filehandles. If two filehandles
from the same server are equal, they MUST refer to the same file.
Servers SHOULD try to maintain a one-to-one correspondence between
filehandles and files but this is not required. Clients MUST use
filehandle comparisons only to improve performance, not for correct
behavior. All clients need to be prepared for situations in which it
cannot be determined whether two filehandles denote the same object
and in such cases, avoid making invalid assumptions which might cause
incorrect behavior. Further discussion of filehandle and attribute
comparison in the context of data caching is presented in the section
"Data Caching and File Identity".
As an example, in the case that two different path names when
traversed at the server terminate at the same filesystem object, the
server SHOULD return the same filehandle for each path. This can
occur if a hard link is used to create two file names which refer to
the same underlying file object and associated data. For example, if
paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
return the same filehandle for both path names traversals.
A persistent filehandle is defined as having a fixed value for the
lifetime of the filesystem object to which it refers. Once the
server creates the filehandle for a filesystem object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts or reboots the NFS server must
honor the same filehandle value as it did in the server's previous
instantiation. Similarly, if the filesystem is migrated, the new NFS
server must honor the same filehandle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
filesystem object is removed. When the server is presented with a
persistent filehandle that refers to a deleted object, it MUST return
an error of NFS4ERR_STALE. A filehandle may become stale when the
filesystem containing the object is no longer available. The file
Shepler, et al. Standards Track [Page 32]
RFC 3530 NFS version 4 Protocol April 2003
system may become unavailable if it exists on removable media and the
media is no longer available at the server or the filesystem in whole
has been destroyed or the filesystem has simply been removed from the
server's name space (i.e., unmounted in a UNIX environment).
A volatile filehandle does not share the same longevity
characteristics of a persistent filehandle. The server may determine
that a volatile filehandle is no longer valid at many different
points in time. If the server can definitively determine that a
volatile filehandle refers to an object that has been removed, the
server should return NFS4ERR_STALE to the client (as is the case for
persistent filehandles). In all other cases where the server
determines that a volatile filehandle can no longer be used, it
should return an error of NFS4ERR_FHEXPIRED.
The mandatory attribute "fh_expire_type" is used by the client to
determine what type of filehandle the server is providing for a
particular filesystem. This attribute is a bitmask with the
following values:
FH4_PERSISTENT
The value of FH4_PERSISTENT is used to indicate a
persistent filehandle, which is valid until the object is
removed from the filesystem. The server will not return
NFS4ERR_FHEXPIRED for this filehandle. FH4_PERSISTENT is
defined as a value in which none of the bits specified
below are set.
FH4_VOLATILE_ANY
The filehandle may expire at any time, except as
specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
FH4_NOEXPIRE_WITH_OPEN
May only be set when FH4_VOLATILE_ANY is set. If this bit
is set, then the meaning of FH4_VOLATILE_ANY is qualified
to exclude any expiration of the filehandle when it is
open.
FH4_VOL_MIGRATION
The filehandle will expire as a result of migration. If
FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.
Shepler, et al. Standards Track [Page 33]
RFC 3530 NFS version 4 Protocol April 2003
FH4_VOL_RENAME
The filehandle will expire during rename. This includes a
rename by the requesting client or a rename by any other
client. If FH4_VOL_ANY is set, FH4_VOL_RENAME is
redundant.
Servers which provide volatile filehandles that may expire while open
(i.e., if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
deny a RENAME or REMOVE that would affect an OPEN file of any of the
components leading to the OPEN file. In addition, the server should
deny all RENAME or REMOVE requests during the grace period upon
server restart.
Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
client to determine that expiration has occurred whenever a specific
event occurs, without an explicit filehandle expiration error from
the server. FH4_VOL_ANY does not provide this form of information.
In situations where the server will expire many, but not all
filehandles upon migration (e.g., all but those that are open),
FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
better choice since the client may not assume that all filehandles
will expire when migration occurs, and it is likely that additional
expirations will occur (as a result of file CLOSE) that are separated
in time from the migration event itself.
A volatile filehandle, while opaque to the client could contain:
[volatile bit = 1 | server boot time | slot | generation number]
o slot is an index in the server volatile filehandle table
o generation number is the generation number for the table
entry/slot
When the client presents a volatile filehandle, the server makes the
following checks, which assume that the check for the volatile bit
has passed. If the server boot time is less than the current server
boot time, return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match, return
NFS4ERR_FHEXPIRED.
When the server reboots, the table is gone (it is volatile).
If volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
Shepler, et al. Standards Track [Page 34]
RFC 3530 NFS version 4 Protocol April 2003
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the filesystem object
in question. With these names, the client should be able to recover
by finding a filehandle in the name space that is still available or
by starting at the root of the server's filesystem name space.
If the expired filehandle refers to an object that has been removed
from the filesystem, obviously the client will not be able to recover
from the expired filehandle.
It is also possible that the expired filehandle refers to a file that
has been renamed. If the file was renamed by another client, again
it is possible that the original client will not be able to recover.
However, in the case that the client itself is renaming the file and
the file is open, it is possible that the client may be able to
recover. The client can determine the new path name based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new path name. The client could also use
the compound operation mechanism to construct a set of operations
like:
RENAME A B
LOOKUP B
GETFH
Note that the COMPOUND procedure does not provide atomicity. This
example only reduces the overhead of recovering from an expired
filehandle.
To meet the requirements of extensibility and increased
interoperability with non-UNIX platforms, attributes must be handled
in a flexible manner. The NFS version 3 fattr3 structure contains a
fixed list of attributes that not all clients and servers are able to
support or care about. The fattr3 structure can not be extended as
new needs arise and it provides no way to indicate non-support. With
the NFS version 4 protocol, the client is able query what attributes
the server supports and construct requests with only those supported
attributes (or a subset thereof).
Shepler, et al. Standards Track [Page 35]
RFC 3530 NFS version 4 Protocol April 2003
To this end, attributes are divided into three groups: mandatory,
recommended, and named. Both mandatory and recommended attributes
are supported in the NFS version 4 protocol by a specific and well-
defined encoding and are identified by number. They are requested by
setting a bit in the bit vector sent in the GETATTR request; the
server response includes a bit vector to list what attributes were
returned in the response. New mandatory or recommended attributes
may be added to the NFS protocol between major revisions by
publishing a standards-track RFC which allocates a new attribute
number value and defines the encoding for the attribute. See the
section "Minor Versioning" for further discussion.
Named attributes are accessed by the new OPENATTR operation, which
accesses a hidden directory of attributes associated with a file
system object. OPENATTR takes a filehandle for the object and
returns the filehandle for the attribute hierarchy. The filehandle
for the named attributes is a directory object accessible by LOOKUP
or READDIR and contains files whose names represent the named
attributes and whose data bytes are the value of the attribute. For
example:
LOOKUP "foo" ; look up file
GETATTR attrbits
OPENATTR ; access foo's named attributes
LOOKUP "x11icon" ; look up specific attribute
READ 0,4096 ; read stream of bytes
Named attributes are intended for data needed by applications rather
than by an NFS client implementation. NFS implementors are strongly
encouraged to define their new attributes as recommended attributes
by bringing them to the IETF standards-track process.
The set of attributes which are classified as mandatory is
deliberately small since servers must do whatever it takes to support
them. A server should support as many of the recommended attributes
as possible but by their definition, the server is not required to
support all of them. Attributes are deemed mandatory if the data is
both needed by a large number of clients and is not otherwise
reasonably computable by the client when support is not provided on
the server.
Note that the hidden directory returned by OPENATTR is a convenience
for protocol processing. The client should not make any assumptions
about the server's implementation of named attributes and whether the
underlying filesystem at the server has a named attribute directory
or not. Therefore, operations such as SETATTR and GETATTR on the
named attribute directory are undefined.
Shepler, et al. Standards Track [Page 36]
RFC 3530 NFS version 4 Protocol April 2003
These MUST be supported by every NFS version 4 client and server in
order to ensure a minimum level of interoperability. The server must
store and return these attributes and the client must be able to
function with an attribute set limited to these attributes. With
just the mandatory attributes some client functionality may be
impaired or limited in some ways. A client may ask for any of these
attributes to be returned by setting a bit in the GETATTR request and
the server must return their value.
These attributes are understood well enough to warrant support in the
NFS version 4 protocol. However, they may not be supported on all
clients and servers. A client may ask for any of these attributes to
be returned by setting a bit in the GETATTR request but must handle
the case where the server does not return them. A client may ask for
the set of attributes the server supports and should not request
attributes the server does not support. A server should be tolerant
of requests for unsupported attributes and simply not return them
rather than considering the request an error. It is expected that
servers will support all attributes they comfortably can and only
fail to support attributes which are difficult to support in their
operating environments. A server should provide attributes whenever
they don't have to "tell lies" to the client. For example, a file
modification time should be either an accurate time or should not be
supported by the server. This will not always be comfortable to
clients but the client is better positioned decide whether and how to
fabricate or construct an attribute or whether to do without the
attribute.
These attributes are not supported by direct encoding in the NFS
Version 4 protocol but are accessed by string names rather than
numbers and correspond to an uninterpreted stream of bytes which are
stored with the filesystem object. The name space for these
attributes may be accessed by using the OPENATTR operation. The
OPENATTR operation returns a filehandle for a virtual "attribute
directory" and further perusal of the name space may be done using
READDIR and LOOKUP operations on this filehandle. Named attributes
may then be examined or changed by normal READ and WRITE and CREATE
operations on the filehandles returned from READDIR and LOOKUP.
Named attributes may have attributes.
Shepler, et al. Standards Track [Page 37]
RFC 3530 NFS version 4 Protocol April 2003
It is recommended that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's filesystem. If a server does support named
attributes, a client which is also able to handle them should be able
to copy a file's data and meta-data with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as
well.
Names of attributes will not be controlled by this document or other
IETF standards track documents. See the section "IANA
Considerations" for further discussion.
Each of the Mandatory and Recommended attributes can be classified in
one of three categories: per server, per filesystem, or per
filesystem object. Note that it is possible that some per filesystem
attributes may vary within the filesystem. See the "homogeneous"
attribute for its definition. Note that the attributes
time_access_set and time_modify_set are not listed in this section
because they are write-only attributes corresponding to time_access
and time_modify, and are used in a special instance of SETATTR.
o The per server attribute is:
lease_time
o The per filesystem attributes are:
supp_attr, fh_expire_type, link_support, symlink_support,
unique_handles, aclsupport, cansettime, case_insensitive,
case_preserving, chown_restricted, files_avail, files_free,
files_total, fs_locations, homogeneous, maxfilesize, maxname,
maxread, maxwrite, no_trunc, space_avail, space_free, space_total,
time_delta
o The per filesystem object attributes are:
type, change, size, named_attr, fsid, rdattr_error, filehandle,
ACL, archive, fileid, hidden, maxlink, mimetype, mode, numlinks,
owner, owner_group, rawdev, space_used, system, time_access,
time_backup, time_create, time_metadata, time_modify,
mounted_on_fileid
For quota_avail_hard, quota_avail_soft, and quota_used see their
definitions below for the appropriate classification.
Shepler, et al. Standards Track [Page 38]
RFC 3530 NFS version 4 Protocol April 2003
Name # DataType Access Description
___________________________________________________________________
supp_attr 0 bitmap READ The bit vector which
would retrieve all
mandatory and
recommended attributes
that are supported for
this object. The
scope of this
attribute applies to
all objects with a
matching fsid.
type 1 nfs4_ftype READ The type of the object
(file, directory,
symlink, etc.)
fh_expire_type 2 uint32 READ Server uses this to
specify filehandle
expiration behavior to
the client. See the
section "Filehandles"
for additional
description.
change 3 uint64 READ A value created by the
server that the client
can use to determine
if file data,
directory contents or
attributes of the
object have been
modified. The server
may return the
object's time_metadata
attribute for this
attribute's value but
only if the filesystem
object can not be
updated more
frequently than the
resolution of
time_metadata.
size 4 uint64 R/W The size of the object
in bytes.
Shepler, et al. Standards Track [Page 39]
RFC 3530 NFS version 4 Protocol April 2003
link_support 5 bool READ True, if the object's
filesystem supports
hard links.
symlink_support 6 bool READ True, if the object's
filesystem supports
symbolic links.
named_attr 7 bool READ True, if this object
has named attributes.
In other words, object
has a non-empty named
attribute directory.
fsid 8 fsid4 READ Unique filesystem
identifier for the
filesystem holding
this object. fsid
contains major and
minor components each
of which are uint64.
unique_handles 9 bool READ True, if two distinct
filehandles guaranteed
to refer to two
different filesystem
objects.
lease_time 10 nfs_lease4 READ Duration of leases at
server in seconds.
rdattr_error 11 enum READ Error returned from
getattr during
readdir.
filehandle 19 nfs_fh4 READ The filehandle of this
object (primarily for
readdir requests).
Shepler, et al. Standards Track [Page 40]
RFC 3530 NFS version 4 Protocol April 2003
Name # Data Type Access Description
_____________________________________________________________________
ACL 12 nfsace4<> R/W The access control
list for the object.
aclsupport 13 uint32 READ Indicates what types
of ACLs are
supported on the
current filesystem.
archive 14 bool R/W True, if this file
has been archived
since the time of
last modification
(deprecated in favor
of time_backup).
cansettime 15 bool READ True, if the server
is able to change
the times for a
filesystem object as
specified in a
SETATTR operation.
case_insensitive 16 bool READ True, if filename
comparisons on this
filesystem are case
insensitive.
case_preserving 17 bool READ True, if filename
case on this
filesystem are
preserved.
chown_restricted 18 bool READ If TRUE, the server
will reject any
request to change
either the owner or
the group associated
with a file if the
caller is not a
privileged user (for
example, "root" in
UNIX operating
environments or in
Windows 2000 the
Shepler, et al. Standards Track [Page 41]
RFC 3530 NFS version 4 Protocol April 2003
"Take Ownership"
privilege).
fileid 20 uint64 READ A number uniquely
identifying the file
within the
filesystem.
files_avail 21 uint64 READ File slots available
to this user on the
filesystem
containing this
object - this should
be the smallest
relevant limit.
files_free 22 uint64 READ Free file slots on
the filesystem
containing this
object - this should
be the smallest
relevant limit.
files_total 23 uint64 READ Total file slots on
the filesystem
containing this
object.
fs_locations 24 fs_locations READ Locations where this
filesystem may be
found. If the
server returns
NFS4ERR_MOVED
as an error, this
attribute MUST be
supported.
hidden 25 bool R/W True, if the file is
considered hidden
with respect to the
Windows API.
homogeneous 26 bool READ True, if this
object's filesystem
is homogeneous,
i.e., are per
filesystem
attributes the same
Shepler, et al. Standards Track [Page 42]
RFC 3530 NFS version 4 Protocol April 2003
for all filesystem's
objects?
maxfilesize 27 uint64 READ Maximum supported
file size for the
filesystem of this
object.
maxlink 28 uint32 READ Maximum number of
links for this
object.
maxname 29 uint32 READ Maximum filename
size supported for
this object.
maxread 30 uint64 READ Maximum read size
supported for this
object.
maxwrite 31 uint64 READ Maximum write size
supported for this
object. This
attribute SHOULD be
supported if the
file is writable.
Lack of this
attribute can
lead to the client
either wasting
bandwidth or not
receiving the best
performance.
mimetype 32 utf8<> R/W MIME body
type/subtype of this
object.
mode 33 mode4 R/W UNIX-style mode and
permission bits for
this object.
no_trunc 34 bool READ True, if a name
longer than name_max
is used, an error be
returned and name is
not truncated.
Shepler, et al. Standards Track [Page 43]
RFC 3530 NFS version 4 Protocol April 2003
numlinks 35 uint32 READ Number of hard links
to this object.
owner 36 utf8<> R/W The string name of
the owner of this
object.
owner_group 37 utf8<> R/W The string name of
the group ownership
of this object.
quota_avail_hard 38 uint64 READ For definition see
"Quota Attributes"
section below.
quota_avail_soft 39 uint64 READ For definition see
"Quota Attributes"
section below.
quota_used 40 uint64 READ For definition see
"Quota Attributes"
section below.
rawdev 41 specdata4 READ Raw device
identifier. UNIX
device major/minor
node information.
If the value of
type is not
NF4BLK or NF4CHR,
the value return
SHOULD NOT be
considered useful.
space_avail 42 uint64 READ Disk space in bytes
available to this
user on the
filesystem
containing this
object - this should
be the smallest
relevant limit.
space_free 43 uint64 READ Free disk space in
bytes on the
filesystem
containing this
object - this should
Shepler, et al. Standards Track [Page 44]
RFC 3530 NFS version 4 Protocol April 2003
be the smallest
relevant limit.
space_total 44 uint64 READ Total disk space in
bytes on the
filesystem
containing this
object.
space_used 45 uint64 READ Number of filesystem
bytes allocated to
this object.
system 46 bool R/W True, if this file
is a "system" file
with respect to the
Windows API.
time_access 47 nfstime4 READ The time of last
access to the object
by a read that was
satisfied by the
server.
time_access_set 48 settime4 WRITE Set the time of last
access to the
object. SETATTR
use only.
time_backup 49 nfstime4 R/W The time of last
backup of the
object.
time_create 50 nfstime4 R/W The time of creation
of the object. This
attribute does not
have any relation to
the traditional UNIX
file attribute
"ctime" or "change
time".
time_delta 51 nfstime4 READ Smallest useful
server time
granularity.
Shepler, et al. Standards Track [Page 45]
RFC 3530 NFS version 4 Protocol April 2003
time_metadata 52 nfstime4 READ The time of last
meta-data
modification of the
object.
time_modify 53 nfstime4 READ The time of last
modification to the
object.
time_modify_set 54 settime4 WRITE Set the time of last
modification to the
object. SETATTR use
only.
mounted_on_fileid 55 uint64 READ Like fileid, but if
the target
filehandle is the
root of a filesystem
return the fileid of
the underlying
directory.
As defined above, the time_access attribute represents the time of
last access to the object by a read that was satisfied by the server.
The notion of what is an "access" depends on server's operating
environment and/or the server's filesystem semantics. For example,
for servers obeying POSIX semantics, time_access would be updated
only by the READLINK, READ, and READDIR operations and not any of the
operations that modify the content of the object. Of course, setting
the corresponding time_access_set attribute is another way to modify
the time_access attribute.
Whenever the file object resides on a writable filesystem, the server
should make best efforts to record time_access into stable storage.
However, to mitigate the performance effects of doing so, and most
especially whenever the server is satisfying the read of the object's
content from its cache, the server MAY cache access time updates and
lazily write them to stable storage. It is also acceptable to give
administrators of the server the option to disable time_access
updates.
Shepler, et al. Standards Track [Page 46]
RFC 3530 NFS version 4 Protocol April 2003
The recommended attributes "owner" and "owner_group" (and also users
and groups within the "acl" attribute) are represented in terms of a
UTF-8 string. To avoid a representation that is tied to a particular
underlying implementation at the client or server, the use of the
UTF-8 string has been chosen. Note that section 6.1 of [RFC2624]
provides additional rationale. It is expected that the client and
server will have their own local representation of owner and
owner_group that is used for local storage or presentation to the end
user. Therefore, it is expected that when these attributes are
transferred between the client and server that the local
representation is translated to a syntax of the form
"user@dns_domain". This will allow for a client and server that do
not use the same local representation the ability to translate to a
common syntax that can be interpreted by both.
Similarly, security principals may be represented in different ways
by different security mechanisms. Servers normally translate these
representations into a common format, generally that used by local
storage, to serve as a means of identifying the users corresponding
to these security principals. When these local identifiers are
translated to the form of the owner attribute, associated with files
created by such principals they identify, in a common format, the
users associated with each corresponding set of security principals.
The translation used to interpret owner and group strings is not
specified as part of the protocol. This allows various solutions to
be employed. For example, a local translation table may be consulted
that maps between a numeric id to the user@dns_domain syntax. A name
service may also be used to accomplish the translation. A server may
provide a more general service, not limited by any particular
translation (which would only translate a limited set of possible
strings) by storing the owner and owner_group attributes in local
storage without any translation or it may augment a translation
method by storing the entire string for attributes for which no
translation is available while using the local representation for
those cases in which a translation is available.
Servers that do not provide support for all possible values of the
owner and owner_group attributes, should return an error
(NFS4ERR_BADOWNER) when a string is presented that has no
translation, as the value to be set for a SETATTR of the owner,
owner_group, or acl attributes. When a server does accept an owner
or owner_group value as valid on a SETATTR (and similarly for the
owner and group strings in an acl), it is promising to return that
same string when a corresponding GETATTR is done. Configuration
changes and ill-constructed name translations (those that contain
Shepler, et al. Standards Track [Page 47]
RFC 3530 NFS version 4 Protocol April 2003
aliasing) may make that promise impossible to honor. Servers should
make appropriate efforts to avoid a situation in which these
attributes have their values changed when no real change to ownership
has occurred.
The "dns_domain" portion of the owner string is meant to be a DNS
domain name. For example, user@ietf.org. Servers should accept as
valid a set of users for at least one domain. A server may treat
other domains as having no valid translations. A more general
service is provided when a server is capable of accepting users for
multiple domains, or for all domains, subject to security
constraints.
In the case where there is no translation available to the client or
server, the attribute value must be constructed without the "@".
Therefore, the absence of the @ from the owner or owner_group
attribute signifies that no translation was available at the sender
and that the receiver of the attribute should not use that string as
a basis for translation into its own internal format. Even though
the attribute value can not be translated, it may still be useful.
In the case of a client, the attribute string may be used for local
display of ownership.
To provide a greater degree of compatibility with previous versions
of NFS (i.e., v2 and v3), which identified users and groups by 32-bit
unsigned uid's and gid's, owner and group strings that consist of
decimal numeric values with no leading zeros can be given a special
interpretation by clients and servers which choose to provide such
support. The receiver may treat such a user or group string as
representing the same user as would be represented by a v2/v3 uid or
gid having the corresponding numeric value. A server is not
obligated to accept such a string, but may return an NFS4ERR_BADOWNER
instead. To avoid this mechanism being used to subvert user and
group translation, so that a client might pass all of the owners and
groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
error when there is a valid translation for the user or owner
designated in this way. In that case, the client must use the
appropriate name@domain string and not the special form for
compatibility.
The owner string "nobody" may be used to designate an anonymous user,
which will be associated with a file created by a security principal
that cannot be mapped through normal means to the owner attribute.
Shepler, et al. Standards Track [Page 48]
RFC 3530 NFS version 4 Protocol April 2003
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) has a "long descriptive
name" [RFC1345] which may or may not included the word "CAPITAL" or
"SMALL". The presence of SMALL or CAPITAL allows an NFS server to
implement unambiguous and efficient table driven mappings for case
insensitive comparisons, and non-case-preserving storage. For
general character handling and internationalization issues, see the
section "Internationalization".
For the attributes related to filesystem quotas, the following
definitions apply:
quota_avail_soft
The value in bytes which represents the amount of additional
disk space that can be allocated to this file or directory
before the user may reasonably be warned. It is understood
that this space may be consumed by allocations to other files
or directories though there is a rule as to which other files
or directories.
quota_avail_hard
The value in bytes which represent the amount of additional
disk space beyond the current allocation that can be allocated
to this file or directory before further allocations will be
refused. It is understood that this space may be consumed by
allocations to other files or directories.
quota_used
The value in bytes which represent the amount of disc space
used by this file or directory and possibly a number of other
similar files or directories, where the set of "similar" meets
at least the criterion that allocating space to any file or
directory in the set will reduce the "quota_avail_hard" of
every other file or directory in the set.
Note that there may be a number of distinct but overlapping
sets of files or directories for which a quota_used value is
maintained (e.g., "all files with a given owner", "all files
with a given group owner", etc.).
The server is at liberty to choose any of those sets but should
do so in a repeatable way. The rule may be configured per-
filesystem or may be "choose the set with the smallest quota".
Shepler, et al. Standards Track [Page 49]
RFC 3530 NFS version 4 Protocol April 2003
The NFS version 4 ACL attribute is an array of access control entries
(ACE). Although, the client can read and write the ACL attribute,
the NFSv4 model is the server does all access control based on the
server's interpretation of the ACL. If at any point the client wants
to check access without issuing an operation that modifies or reads
data or metadata, the client can use the OPEN and ACCESS operations
to do so. There are various access control entry types, as defined
in the Section "ACE type". The server is able to communicate which
ACE types are supported by returning the appropriate value within the
aclsupport attribute. Each ACE covers one or more operations on a
file or directory as described in the Section "ACE Access Mask". It
may also contain one or more flags that modify the semantics of the
ACE as defined in the Section "ACE flag".
The NFS ACE attribute is defined as follows:
typedef uint32_t acetype4;
typedef uint32_t aceflag4;
typedef uint32_t acemask4;
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8str_mixed who;
};
To determine if a request succeeds, each nfsace4 entry is processed
in order by the server. Only ACEs which have a "who" that matches
the requester are considered. Each ACE is processed until all of the
bits of the requester's access have been ALLOWED. Once a bit (see
below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
considered in the processing of later ACEs. If an ACCESS_DENIED_ACE
is encountered where the requester's access still has unALLOWED bits
in common with the "access_mask" of the ACE, the request is denied.
However, unlike the ALLOWED and DENIED ACE types, the ALARM and AUDIT
ACE types do not affect a requester's access, and instead are for
triggering events as a result of a requester's access attempt.
Therefore, all AUDIT and ALARM ACEs are processed until end of the
ACL. When the ACL is fully processed, if there are bits in
requester's mask that have not been considered whether the server
allows or denies the access is undefined. If there is a mode
attribute on the file, then this cannot happen, since the mode's
MODE4_*OTH bits will map to EVERYONE@ ACEs that unambiguously specify
the requester's access.
Shepler, et al. Standards Track [Page 50]
RFC 3530 NFS version 4 Protocol April 2003
The NFS version 4 ACL model is quite rich. Some server platforms may
provide access control functionality that goes beyond the UNIX-style
mode attribute, but which is not as rich as the NFS ACL model. So
that users can take advantage of this more limited functionality, the
server may indicate that it supports ACLs as long as it follows the
guidelines for mapping between its ACL model and the NFS version 4
ACL model.
The situation is complicated by the fact that a server may have
multiple modules that enforce ACLs. For example, the enforcement for
NFS version 4 access may be different from the enforcement for local
access, and both may be different from the enforcement for access
through other protocols such as SMB. So it may be useful for a
server to accept an ACL even if not all of its modules are able to
support it.
The guiding principle in all cases is that the server must not accept
ACLs that appear to make the file more secure than it really is.
Type Description
_____________________________________________________
ALLOW Explicitly grants the access defined in
acemask4 to the file or directory.
DENY Explicitly denies the access defined in
acemask4 to the file or directory.
AUDIT LOG (system dependent) any access
attempt to a file or directory which
uses any of the access methods specified
in acemask4.
ALARM Generate a system ALARM (system
dependent) when any access attempt is
made to a file or directory for the
access methods specified in acemask4.
A server need not support all of the above ACE types. The bitmask
constants used to represent the above definitions within the
aclsupport attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
Shepler, et al. Standards Track [Page 51]
RFC 3530 NFS version 4 Protocol April 2003
The semantics of the "type" field follow the descriptions provided
above.
The constants used for the type field (acetype4) are as follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
Clients should not attempt to set an ACE unless the server claims
support for that ACE type. If the server receives a request to set
an ACE that it cannot store, it MUST reject the request with
NFS4ERR_ATTRNOTSUPP. If the server receives a request to set an ACE
that it can store but cannot enforce, the server SHOULD reject the
request with NFS4ERR_ATTRNOTSUPP.
Example: suppose a server can enforce NFS ACLs for NFS access but
cannot enforce ACLs for local access. If arbitrary processes can run
on the server, then the server SHOULD NOT indicate ACL support. On
the other hand, if only trusted administrative programs run locally,
then the server may indicate ACL support.
The access_mask field contains values based on the following:
Access Description
_______________________________________________________________
READ_DATA Permission to read the data of the file
LIST_DIRECTORY Permission to list the contents of a
directory
WRITE_DATA Permission to modify the file's data
ADD_FILE Permission to add a new file to a
directory
APPEND_DATA Permission to append data to a file
ADD_SUBDIRECTORY Permission to create a subdirectory to a
directory
READ_NAMED_ATTRS Permission to read the named attributes
of a file
WRITE_NAMED_ATTRS Permission to write the named attributes
of a file
EXECUTE Permission to execute a file
DELETE_CHILD Permission to delete a file or directory
within a directory
READ_ATTRIBUTES The ability to read basic attributes
(non-acls) of a file
WRITE_ATTRIBUTES Permission to change basic attributes
Shepler, et al. Standards Track [Page 52]
RFC 3530 NFS version 4 Protocol April 2003
(non-acls) of a file
DELETE Permission to Delete the file
READ_ACL Permission to Read the ACL
WRITE_ACL Permission to Write the ACL
WRITE_OWNER Permission to change the owner
SYNCHRONIZE Permission to access file locally at the
server with synchronous reads and writes
The bitmask constants used for the access mask field are as follows:
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
Server implementations need not provide the granularity of control
that is implied by this list of masks. For example, POSIX-based
systems might not distinguish APPEND_DATA (the ability to append to a
file) from WRITE_DATA (the ability to modify existing contents); both
masks would be tied to a single "write" permission. When such a
server returns attributes to the client, it would show both
APPEND_DATA and WRITE_DATA if and only if the write permission is
enabled.
If a server receives a SETATTR request that it cannot accurately
implement, it should error in the direction of more restricted
access. For example, suppose a server cannot distinguish overwriting
data from appending new data, as described in the previous paragraph.
If a client submits an ACE where APPEND_DATA is set but WRITE_DATA is
not (or vice versa), the server should reject the request with
NFS4ERR_ATTRNOTSUPP. Nonetheless, if the ACE has type DENY, the
server may silently turn on the other bit, so that both APPEND_DATA
and WRITE_DATA are denied.
Shepler, et al. Standards Track [Page 53]
RFC 3530 NFS version 4 Protocol April 2003
The "flag" field contains values based on the following descriptions.
ACE4_FILE_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new non-directory file created.
ACE4_DIRECTORY_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new directory created.
ACE4_INHERIT_ONLY_ACE
Can be placed on a directory but does not apply to the directory,
only to newly created files/directories as specified by the above
two flags.
ACE4_NO_PROPAGATE_INHERIT_ACE
Can be placed on a directory. Normally when a new directory is
created and an ACE exists on the parent directory which is marked
ACL4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new
directory. One for the directory itself and one which is an
inheritable ACE for newly created directories. This flag tells
the server to not place an ACE on the newly created directory
which is inheritable by subdirectories of the created directory.
ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
ACL4_FAILED_ACCESS_ACE_FLAG
The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only to
ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
(ALARM) ACE types. If during the processing of the file's ACL,
the server encounters an AUDIT or ALARM ACE that matches the
principal attempting the OPEN, the server notes that fact, and the
presence, if any, of the SUCCESS and FAILED flags encountered in
the AUDIT or ALARM ACE. Once the server completes the ACL
processing, and the share reservation processing, and the OPEN
call, it then notes if the OPEN succeeded or failed. If the OPEN
succeeded, and if the SUCCESS flag was set for a matching AUDIT or
ALARM, then the appropriate AUDIT or ALARM event occurs. If the
OPEN failed, and if the FAILED flag was set for the matching AUDIT
or ALARM, then the appropriate AUDIT or ALARM event occurs.
Clearly either or both of the SUCCESS or FAILED can be set, but if
neither is set, the AUDIT or ALARM ACE is not useful.
Shepler, et al. Standards Track [Page 54]
RFC 3530 NFS version 4 Protocol April 2003
The previously described processing applies to that of the ACCESS
operation as well. The difference being that "success" or
"failure" does not mean whether ACCESS returns NFS4_OK or not.
Success means whether ACCESS returns all requested and supported
bits. Failure means whether ACCESS failed to return a bit that
was requested and supported.
ACE4_IDENTIFIER_GROUP
Indicates that the "who" refers to a GROUP as defined under UNIX.
The bitmask constants used for the flag field are as follows:
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
A server need not support any of these flags. If the server supports
flags that are similar to, but not exactly the same as, these flags,
the implementation may define a mapping between the protocol-defined
flags and the implementation-defined flags. Again, the guiding
principle is that the file not appear to be more secure than it
really is.
For example, suppose a client tries to set an ACE with
ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE. If the
server does not support any form of ACL inheritance, the server
should reject the request with NFS4ERR_ATTRNOTSUPP. If the server
supports a single "inherit ACE" flag that applies to both files and
directories, the server may reject the request (i.e., requiring the
client to set both the file and directory inheritance flags). The
server may also accept the request and silently turn on the
ACE4_DIRECTORY_INHERIT_ACE flag.
There are several special identifiers ("who") which need to be
understood universally, rather than in the context of a particular
DNS domain. Some of these identifiers cannot be understood when an
NFS client accesses the server, but have meaning when a local process
accesses the file. The ability to display and modify these
permissions is permitted over NFS, even if none of the access methods
on the server understands the identifiers.
Shepler, et al. Standards Track [Page 55]
RFC 3530 NFS version 4 Protocol April 2003
Who Description
_______________________________________________________________
"OWNER" The owner of the file.
"GROUP" The group associated with the file.
"EVERYONE" The world.
"INTERACTIVE" Accessed from an interactive terminal.
"NETWORK" Accessed via the network.
"DIALUP" Accessed as a dialup user to the server.
"BATCH" Accessed from a batch job.
"ANONYMOUS" Accessed without any authentication.
"AUTHENTICATED" Any authenticated user (opposite of
ANONYMOUS)
"SERVICE" Access from a system service.
To avoid conflict, these special identifiers are distinguish by an
appended "@" and should appear in the form "xxxx@" (note: no domain
name after the "@"). For example: ANONYMOUS@.
The NFS version 4 mode attribute is based on the UNIX mode bits. The
following bits are defined:
const MODE4_SUID = 0x800; /* set user id on execution */
const MODE4_SGID = 0x400; /* set group id on execution */
const MODE4_SVTX = 0x200; /* save text even after use */
const MODE4_RUSR = 0x100; /* read permission: owner */
const MODE4_WUSR = 0x080; /* write permission: owner */
const MODE4_XUSR = 0x040; /* execute permission: owner */
const MODE4_RGRP = 0x020; /* read permission: group */
const MODE4_WGRP = 0x010; /* write permission: group */
const MODE4_XGRP = 0x008; /* execute permission: group */
const MODE4_ROTH = 0x004; /* read permission: other */
const MODE4_WOTH = 0x002; /* write permission: other */
const MODE4_XOTH = 0x001; /* execute permission: other */
Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
identified in the owner attribute. Bits MODE4_RGRP, MODE4_WGRP, and
MODE4_XGRP apply to the principals identified in the owner_group
attribute. Bits MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any
principal that does not match that in the owner group, and does not
have a group matching that of the owner_group attribute.
The remaining bits are not defined by this protocol and MUST NOT be
used. The minor version mechanism must be used to define further bit
usage.
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Note that in UNIX, if a file has the MODE4_SGID bit set and no
MODE4_XGRP bit set, then READ and WRITE must use mandatory file
locking.
The server that supports both mode and ACL must take care to
synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
ACEs which have respective who fields of "OWNER@", "GROUP@", and
"EVERYONE@" so that the client can see semantically equivalent access
permissions exist whether the client asks for owner, owner_group and
mode attributes, or for just the ACL.
Because the mode attribute includes bits (e.g., MODE4_SVTX) that have
nothing to do with ACL semantics, it is permitted for clients to
specify both the ACL attribute and mode in the same SETATTR
operation. However, because there is no prescribed order for
processing the attributes in a SETATTR, the client must ensure that
ACL attribute, if specified without mode, would produce the desired
mode bits, and conversely, the mode attribute if specified without
ACL, would produce the desired "OWNER@", "GROUP@", and "EVERYONE@"
ACEs.
UNIX-based operating environments connect a filesystem into the
namespace by connecting (mounting) the filesystem onto the existing
file object (the mount point, usually a directory) of an existing
filesystem. When the mount point's parent directory is read via an
API like readdir(), the return results are directory entries, each
with a component name and a fileid. The fileid of the mount point's
directory entry will be different from the fileid that the stat()
system call returns. The stat() system call is returning the fileid
of the root of the mounted filesystem, whereas readdir() is returning
the fileid stat() would have returned before any filesystems were
mounted on the mount point.
Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
to cross other filesystems. The client detects the filesystem
crossing whenever the filehandle argument of LOOKUP has an fsid
attribute different from that of the filehandle returned by LOOKUP.
A UNIX-based client will consider this a "mount point crossing".
UNIX has a legacy scheme for allowing a process to determine its
current working directory. This relies on readdir() of a mount
point's parent and stat() of the mount point returning fileids as
previously described. The mounted_on_fileid attribute corresponds to
the fileid that readdir() would have returned as described
previously.
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While the NFS version 4 client could simply fabricate a fileid
corresponding to what mounted_on_fileid provides (and if the server
does not support mounted_on_fileid, the client has no choice), there
is a risk that the client will generate a fileid that conflicts with
one that is already assigned to another object in the filesystem.
Instead, if the server can provide the mounted_on_fileid, the
potential for client operational problems in this area is eliminated.
If the server detects that there is no mounted point at the target
file object, then the value for mounted_on_fileid that it returns is
the same as that of the fileid attribute.
The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
provide it if possible, and for a UNIX-based server, this is
straightforward. Usually, mounted_on_fileid will be requested during
a READDIR operation, in which case it is trivial (at least for UNIX-
based servers) to return mounted_on_fileid since it is equal to the
fileid of a directory entry returned by readdir(). If
mounted_on_fileid is requested in a GETATTR operation, the server
should obey an invariant that has it returning a value that is equal
to the file object's entry in the object's parent directory, i.e.,
what readdir() would have returned. Some operating environments
allow a series of two or more filesystems to be mounted onto a single
mount point. In this case, for the server to obey the aforementioned
invariant, it will need to find the base mount point, and not the
intermediate mount points.
With the use of the recommended attribute "fs_locations", the NFS
version 4 server has a method of providing filesystem migration or
replication services. For the purposes of migration and replication,
a filesystem will be defined as all files that share a given fsid
(both major and minor values are the same).
The fs_locations attribute provides a list of filesystem locations.
These locations are specified by providing the server name (either
DNS domain or IP address) and the path name representing the root of
the filesystem. Depending on the type of service being provided, the
list will provide a new location or a set of alternate locations for
the filesystem. The client will use this information to redirect its
requests to the new server.
It is expected that filesystem replication will be used in the case
of read-only data. Typically, the filesystem will be replicated on
two or more servers. The fs_locations attribute will provide the
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list of these locations to the client. On first access of the
filesystem, the client should obtain the value of the fs_locations
attribute. If, in the future, the client finds the server
unresponsive, the client may attempt to use another server specified
by fs_locations.
If applicable, the client must take the appropriate steps to recover
valid filehandles from the new server. This is described in more
detail in the following sections.
Filesystem migration is used to move a filesystem from one server to
another. Migration is typically used for a filesystem that is
writable and has a single copy. The expected use of migration is for
load balancing or general resource reallocation. The protocol does
not specify how the filesystem will be moved between servers. This
server-to-server transfer mechanism is left to the server
implementor. However, the method used to communicate the migration
event between client and server is specified here.
Once the servers participating in the migration have completed the
move of the filesystem, the error NFS4ERR_MOVED will be returned for
subsequent requests received by the original server. The
NFS4ERR_MOVED error is returned for all operations except PUTFH and
GETATTR. Upon receiving the NFS4ERR_MOVED error, the client will
obtain the value of the fs_locations attribute. The client will then
use the contents of the attribute to redirect its requests to the
specified server. To facilitate the use of GETATTR, operations such
as PUTFH must also be accepted by the server for the migrated file
system's filehandles. Note that if the server returns NFS4ERR_MOVED,
the server MUST support the fs_locations attribute.
If the client requests more attributes than just fs_locations, the
server may return fs_locations only. This is to be expected since
the server has migrated the filesystem and may not have a method of
obtaining additional attribute data.
The server implementor needs to be careful in developing a migration
solution. The server must consider all of the state information
clients may have outstanding at the server. This includes but is not
limited to locking/share state, delegation state, and asynchronous
file writes which are represented by WRITE and COMMIT verifiers. The
server should strive to minimize the impact on its clients during and
after the migration process.
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The fs_location attribute is structured in the following way:
struct fs_location {
utf8str_cis server<>;
pathname4 rootpath;
};
struct fs_locations {
pathname4 fs_root;
fs_location locations<>;
};
The fs_location struct is used to represent the location of a
filesystem by providing a server name and the path to the root of the
filesystem. For a multi-homed server or a set of servers that use
the same rootpath, an array of server names may be provided. An
entry in the server array is an UTF8 string and represents one of a
traditional DNS host name, IPv4 address, or IPv6 address. It is not
a requirement that all servers that share the same rootpath be listed
in one fs_location struct. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location entries in the fs_locations attribute.
The fs_locations struct and attribute then contains an array of
locations. Since the name space of each server may be constructed
differently, the "fs_root" field is provided. The path represented
by fs_root represents the location of the filesystem in the server's
name space. Therefore, the fs_root path is only associated with the
server from which the fs_locations attribute was obtained. The
fs_root path is meant to aid the client in locating the filesystem at
the various servers listed.
As an example, there is a replicated filesystem located at two
servers (servA and servB). At servA the filesystem is located at
path "/a/b/c". At servB the filesystem is located at path "/x/y/z".
In this example the client accesses the filesystem first at servA
with a multi-component lookup path of "/a/b/c/d". Since the client
used a multi-component lookup to obtain the filehandle at "/a/b/c/d",
it is unaware that the filesystem's root is located in servA's name
space at "/a/b/c". When the client switches to servB, it will need
to determine that the directory it first referenced at servA is now
represented by the path "/x/y/z/d" on servB. To facilitate this, the
fs_locations attribute provided by servA would have a fs_root value
of "/a/b/c" and two entries in fs_location. One entry in fs_location
will be for itself (servA) and the other will be for servB with a
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path of "/x/y/z". With this information, the client is able to
substitute "/x/y/z" for the "/a/b/c" at the beginning of its access
path and construct "/x/y/z/d" to use for the new server.
See the section "Security Considerations" for a discussion on the
recommendations for the security flavor to be used by any GETATTR
operation that requests the "fs_locations" attribute.
Filehandles for filesystems that are replicated or migrated generally
have the same semantics as for filesystems that are not replicated or
migrated. For example, if a filesystem has persistent filehandles
and it is migrated to another server, the filehandle values for the
filesystem will be valid at the new server.
For volatile filehandles, the servers involved likely do not have a
mechanism to transfer filehandle format and content between
themselves. Therefore, a server may have difficulty in determining
if a volatile filehandle from an old server should return an error of
NFS4ERR_FHEXPIRED. Therefore, the client is informed, with the use
of the fh_expire_type attribute, whether volatile filehandles will
expire at the migration or replication event. If the bit
FH4_VOL_MIGRATION is set in the fh_expire_type attribute, the client
must treat the volatile filehandle as if the server had returned the
NFS4ERR_FHEXPIRED error. At the migration or replication event in
the presence of the FH4_VOL_MIGRATION bit, the client will not
present the original or old volatile filehandle to the new server.
The client will start its communication with the new server by
recovering its filehandles using the saved file names.
On a UNIX server the name space describes all the files reachable by
pathnames under the root directory or "/". On a Windows NT server
the name space constitutes all the files on disks named by mapped
disk letters. NFS server administrators rarely make the entire
server's filesystem name space available to NFS clients. More often
portions of the name space are made available via an "export"
feature. In previous versions of the NFS protocol, the root
filehandle for each export is obtained through the MOUNT protocol;
the client sends a string that identifies the export of name space
and the server returns the root filehandle for it. The MOUNT
protocol supports an EXPORTS procedure that will enumerate the
server's exports.
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The NFS version 4 protocol provides a root filehandle that clients
can use to obtain filehandles for these exports via a multi-component
LOOKUP. A common user experience is to use a graphical user
interface (perhaps a file "Open" dialog window) to find a file via
progressive browsing through a directory tree. The client must be
able to move from one export to another export via single-component,
progressive LOOKUP operations.
This style of browsing is not well supported by the NFS version 2 and
3 protocols. The client expects all LOOKUP operations to remain
within a single server filesystem. For example, the device attribute
will not change. This prevents a client from taking name space paths
that span exports.
An automounter on the client can obtain a snapshot of the server's
name space using the EXPORTS procedure of the MOUNT protocol. If it
understands the server's pathname syntax, it can create an image of
the server's name space on the client. The parts of the name space
that are not exported by the server are filled in with a "pseudo
filesystem" that allows the user to browse from one mounted
filesystem to another. There is a drawback to this representation of
the server's name space on the client: it is static. If the server
administrator adds a new export the client will be unaware of it.
NFS version 4 servers avoid this name space inconsistency by
presenting all the exports within the framework of a single server
name space. An NFS version 4 client uses LOOKUP and READDIR
operations to browse seamlessly from one export to another. Portions
of the server name space that are not exported are bridged via a
"pseudo filesystem" that provides a view of exported directories
only. A pseudo filesystem has a unique fsid and behaves like a
normal, read only filesystem.
Based on the construction of the server's name space, it is possible
that multiple pseudo filesystems may exist. For example,
/a pseudo filesystem
/a/b real filesystem
/a/b/c pseudo filesystem
/a/b/c/d real filesystem
Each of the pseudo filesystems are considered separate entities and
therefore will have a unique fsid.
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The DOS and Windows operating environments are sometimes described as
having "multiple roots". Filesystems are commonly represented as
disk letters. MacOS represents filesystems as top level names. NFS
version 4 servers for these platforms can construct a pseudo file
system above these root names so that disk letters or volume names
are simply directory names in the pseudo root.
The nature of the server's pseudo filesystem is that it is a logical
representation of filesystem(s) available from the server.
Therefore, the pseudo filesystem is most likely constructed
dynamically when the server is first instantiated. It is expected
that the pseudo filesystem may not have an on disk counterpart from
which persistent filehandles could be constructed. Even though it is
preferable that the server provide persistent filehandles for the
pseudo filesystem, the NFS client should expect that pseudo file
system filehandles are volatile. This can be confirmed by checking
the associated "fh_expire_type" attribute for those filehandles in
question. If the filehandles are volatile, the NFS client must be
prepared to recover a filehandle value (e.g., with a multi-component
LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.
If the server's root filesystem is exported, one might conclude that
a pseudo-filesystem is not needed. This would be wrong. Assume the
following filesystems on a server:
/ disk1 (exported)
/a disk2 (not exported)
/a/b disk3 (exported)
Because disk2 is not exported, disk3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo-filesystem.
The server filesystem environment may be constructed in such a way
that one filesystem contains a directory which is 'covered' or
mounted upon by a second filesystem. For example:
/a/b (filesystem 1)
/a/b/c/d (filesystem 2)
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The pseudo filesystem for this server may be constructed to look
like:
/ (place holder/not exported)
/a/b (filesystem 1)
/a/b/c/d (filesystem 2)
It is the server's responsibility to present the pseudo filesystem
that is complete to the client. If the client sends a lookup request
for the path "/a/b/c/d", the server's response is the filehandle of
the filesystem "/a/b/c/d". In previous versions of the NFS protocol,
the server would respond with the filehandle of directory "/a/b/c/d"
within the filesystem "/a/b".
The NFS client will be able to determine if it crosses a server mount
point by a change in the value of the "fsid" attribute.
The application of the server's security policy needs to be carefully
considered by the implementor. One may choose to limit the
viewability of portions of the pseudo filesystem based on the
server's perception of the client's ability to authenticate itself
properly. However, with the support of multiple security mechanisms
and the ability to negotiate the appropriate use of these mechanisms,
the server is unable to properly determine if a client will be able
to authenticate itself. If, based on its policies, the server
chooses to limit the contents of the pseudo filesystem, the server
may effectively hide filesystems from a client that may otherwise
have legitimate access.
As suggested practice, the server should apply the security policy of
a shared resource in the server's namespace to the components of the
resource's ancestors. For example:
/
/a/b
/a/b/c
The /a/b/c directory is a real filesystem and is the shared resource.
The security policy for /a/b/c is Kerberos with integrity. The
server should apply the same security policy to /, /a, and /a/b.
This allows for the extension of the protection of the server's
namespace to the ancestors of the real shared resource.
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For the case of the use of multiple, disjoint security mechanisms in
the server's resources, the security for a particular object in the
server's namespace should be the union of all security mechanisms of
all direct descendants.
Integrating locking into the NFS protocol necessarily causes it to be
stateful. With the inclusion of share reservations the protocol
becomes substantially more dependent on state than the traditional
combination of NFS and NLM [XNFS]. There are three components to
making this state manageable:
o Clear division between client and server
o Ability to reliably detect inconsistency in state between client
and server
o Simple and robust recovery mechanisms
In this model, the server owns the state information. The client
communicates its view of this state to the server as needed. The
client is also able to detect inconsistent state before modifying a
file.
To support Win32 share reservations it is necessary to atomically
OPEN or CREATE files. Having a separate share/unshare operation
would not allow correct implementation of the Win32 OpenFile API. In
order to correctly implement share semantics, the previous NFS
protocol mechanisms used when a file is opened or created (LOOKUP,
CREATE, ACCESS) need to be replaced. The NFS version 4 protocol has
an OPEN operation that subsumes the NFS version 3 methodology of
LOOKUP, CREATE, and ACCESS. However, because many operations require
a filehandle, the traditional LOOKUP is preserved to map a file name
to filehandle without establishing state on the server. The policy
of granting access or modifying files is managed by the server based
on the client's state. These mechanisms can implement policy ranging
from advisory only locking to full mandatory locking.
It is assumed that manipulating a lock is rare when compared to READ
and WRITE operations. It is also assumed that crashes and network
partitions are relatively rare. Therefore it is important that the
READ and WRITE operations have a lightweight mechanism to indicate if
they possess a held lock. A lock request contains the heavyweight
information required to establish a lock and uniquely define the lock
owner.
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The following sections describe the transition from the heavy weight
information to the eventual stateid used for most client and server
locking and lease interactions.
For each LOCK request, the client must identify itself to the server.
This is done in such a way as to allow for correct lock
identification and crash recovery. A sequence of a SETCLIENTID
operation followed by a SETCLIENTID_CONFIRM operation is required to
establish the identification onto the server. Establishment of
identification by a new incarnation of the client also has the effect
of immediately breaking any leased state that a previous incarnation
of the client might have had on the server, as opposed to forcing the
new client incarnation to wait for the leases to expire. Breaking
the lease state amounts to the server removing all lock, share
reservation, and, where the server is not supporting the
CLAIM_DELEGATE_PREV claim type, all delegation state associated with
same client with the same identity. For discussion of delegation
state recovery, see the section "Delegation Recovery".
Client identification is encapsulated in the following structure:
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
The first field, verifier is a client incarnation verifier that is
used to detect client reboots. Only if the verifier is different
from that which the server has previously recorded the client (as
identified by the second field of the structure, id) does the server
start the process of canceling the client's leased state.
The second field, id is a variable length string that uniquely
defines the client.
There are several considerations for how the client generates the id
string:
o The string should be unique so that multiple clients do not
present the same string. The consequences of two clients
presenting the same string range from one client getting an error
to one client having its leased state abruptly and unexpectedly
canceled.
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o The string should be selected so the subsequent incarnations
(e.g., reboots) of the same client cause the client to present the
same string. The implementor is cautioned against an approach
that requires the string to be recorded in a local file because
this precludes the use of the implementation in an environment
where there is no local disk and all file access is from an NFS
version 4 server.
o The string should be different for each server network address
that the client accesses, rather than common to all server network
addresses. The reason is that it may not be possible for the
client to tell if the same server is listening on multiple network
addresses. If the client issues SETCLIENTID with the same id
string to each network address of such a server, the server will
think it is the same client, and each successive SETCLIENTID will
cause the server to begin the process of removing the client's
previous leased state.
o The algorithm for generating the string should not assume that the
client's network address won't change. This includes changes
between client incarnations and even changes while the client is
stilling running in its current incarnation. This means that if
the client includes just the client's and server's network address
in the id string, there is a real risk, after the client gives up
the network address, that another client, using a similar
algorithm for generating the id string, will generate a
conflicting id string.
Given the above considerations, an example of a well generated id
string is one that includes:
o The server's network address.
o The client's network address.
o For a user level NFS version 4 client, it should contain
additional information to distinguish the client from other user
level clients running on the same host, such as a process id or
other unique sequence.
o Additional information that tends to be unique, such as one or
more of:
- The client machine's serial number (for privacy reasons, it is
best to perform some one way function on the serial number).
- A MAC address.
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RFC 3530 NFS version 4 Protocol April 2003
- The timestamp of when the NFS version 4 software was first
installed on the client (though this is subject to the
previously mentioned caution about using information that is
stored in a file, because the file might only be accessible
over NFS version 4).
- A true random number. However since this number ought to be
the same between client incarnations, this shares the same
problem as that of the using the timestamp of the software
installation.
As a security measure, the server MUST NOT cancel a client's leased
state if the principal established the state for a given id string is
not the same as the principal issuing the SETCLIENTID.
Note that SETCLIENTID and SETCLIENTID_CONFIRM has a secondary purpose
of establishing the information the server needs to make callbacks to
the client for purpose of supporting delegations. It is permitted to
change this information via SETCLIENTID and SETCLIENTID_CONFIRM
within the same incarnation of the client without removing the
client's leased state.
Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
completed, the client uses the shorthand client identifier, of type
clientid4, instead of the longer and less compact nfs_client_id4
structure. This shorthand client identifier (a clientid) is assigned
by the server and should be chosen so that it will not conflict with
a clientid previously assigned by the server. This applies across
server restarts or reboots. When a clientid is presented to a server
and that clientid is not recognized, as would happen after a server
reboot, the server will reject the request with the error
NFS4ERR_STALE_CLIENTID. When this happens, the client must obtain a
new clientid by use of the SETCLIENTID operation and then proceed to
any other necessary recovery for the server reboot case (See the
section "Server Failure and Recovery").
The client must also employ the SETCLIENTID operation when it
receives a NFS4ERR_STALE_STATEID error using a stateid derived from
its current clientid, since this also indicates a server reboot which
has invalidated the existing clientid (see the next section
"lock_owner and stateid Definition" for details).
See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
for a complete specification of the operations.
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If the server determines that the client holds no associated state
for its clientid, the server may choose to release the clientid. The
server may make this choice for an inactive client so that resources
are not consumed by those intermittently active clients. If the
client contacts the server after this release, the server must ensure
the client receives the appropriate error so that it will use the
SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.
It should be clear that the server must be very hesitant to release a
clientid since the resulting work on the client to recover from such
an event will be the same burden as if the server had failed and
restarted. Typically a server would not release a clientid unless
there had been no activity from that client for many minutes.
Note that if the id string in a SETCLIENTID request is properly
constructed, and if the client takes care to use the same principal
for each successive use of SETCLIENTID, then, barring an active
denial of service attack, NFS4ERR_CLID_INUSE should never be
returned.
However, client bugs, server bugs, or perhaps a deliberate change of
the principal owner of the id string (such as the case of a client
that changes security flavors, and under the new flavor, there is no
mapping to the previous owner) will in rare cases result in
NFS4ERR_CLID_INUSE.
In that event, when the server gets a SETCLIENTID for a client id
that currently has no state, or it has state, but the lease has
expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
allow the SETCLIENTID, and confirm the new clientid if followed by
the appropriate SETCLIENTID_CONFIRM.
When requesting a lock, the client must present to the server the
clientid and an identifier for the owner of the requested lock.
These two fields are referred to as the lock_owner and the definition
of those fields are:
o A clientid returned by the server as part of the client's use of
the SETCLIENTID operation.
o A variable length opaque array used to uniquely define the owner
of a lock managed by the client.
This may be a thread id, process id, or other unique value.
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When the server grants the lock, it responds with a unique stateid.
The stateid is used as a shorthand reference to the lock_owner, since
the server will be maintaining the correspondence between them.
The server is free to form the stateid in any manner that it chooses
as long as it is able to recognize invalid and out-of-date stateids.
This requirement includes those stateids generated by earlier
instances of the server. From this, the client can be properly
notified of a server restart. This notification will occur when the
client presents a stateid to the server from a previous
instantiation.
The server must be able to distinguish the following situations and
return the error as specified:
o The stateid was generated by an earlier server instance (i.e.,
before a server reboot). The error NFS4ERR_STALE_STATEID should
be returned.
o The stateid was generated by the current server instance but the
stateid no longer designates the current locking state for the
lockowner-file pair in question (i.e., one or more locking
operations has occurred). The error NFS4ERR_OLD_STATEID should be
returned.
This error condition will only occur when the client issues a
locking request which changes a stateid while an I/O request that
uses that stateid is outstanding.
o The stateid was generated by the current server instance but the
stateid does not designate a locking state for any active
lockowner-file pair. The error NFS4ERR_BAD_STATEID should be
returned.
This error condition will occur when there has been a logic error
on the part of the client or server. This should not happen.
One mechanism that may be used to satisfy these requirements is for
the server to,
o divide the "other" field of each stateid into two fields:
- A server verifier which uniquely designates a particular server
instantiation.
- An index into a table of locking-state structures.
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o utilize the "seqid" field of each stateid, such that seqid is
monotonically incremented for each stateid that is associated with
the same index into the locking-state table.
By matching the incoming stateid and its field values with the state
held at the server, the server is able to easily determine if a
stateid is valid for its current instantiation and state. If the
stateid is not valid, the appropriate error can be supplied to the
client.
All READ, WRITE and SETATTR operations contain a stateid. For the
purposes of this section, SETATTR operations which change the size
attribute of a file are treated as if they are writing the area
between the old and new size (i.e., the range truncated or added to
the file by means of the SETATTR), even where SETATTR is not
explicitly mentioned in the text.
If the lock_owner performs a READ or WRITE in a situation in which it
has established a lock or share reservation on the server (any OPEN
constitutes a share reservation) the stateid (previously returned by
the server) must be used to indicate what locks, including both
record locks and share reservations, are held by the lockowner. If
no state is established by the client, either record lock or share
reservation, a stateid of all bits 0 is used. Regardless whether a
stateid of all bits 0, or a stateid returned by the server is used,
if there is a conflicting share reservation or mandatory record lock
held on the file, the server MUST refuse to service the READ or WRITE
operation.
Share reservations are established by OPEN operations and by their
nature are mandatory in that when the OPEN denies READ or WRITE
operations, that denial results in such operations being rejected
with error NFS4ERR_LOCKED. Record locks may be implemented by the
server as either mandatory or advisory, or the choice of mandatory or
advisory behavior may be determined by the server on the basis of the
file being accessed (for example, some UNIX-based servers support a
"mandatory lock bit" on the mode attribute such that if set, record
locks are required on the file before I/O is possible). When record
locks are advisory, they only prevent the granting of conflicting
lock requests and have no effect on READs or WRITEs. Mandatory
record locks, however, prevent conflicting I/O operations. When they
are attempted, they are rejected with NFS4ERR_LOCKED. When the
client gets NFS4ERR_LOCKED on a file it knows it has the proper share
reservation for, it will need to issue a LOCK request on the region
Shepler, et al. Standards Track [Page 71]
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of the file that includes the region the I/O was to be performed on,
with an appropriate locktype (i.e., READ*_LT for a READ operation,
WRITE*_LT for a WRITE operation).
With NFS version 3, there was no notion of a stateid so there was no
way to tell if the application process of the client sending the READ
or WRITE operation had also acquired the appropriate record lock on
the file. Thus there was no way to implement mandatory locking.
With the stateid construct, this barrier has been removed.
Note that for UNIX environments that support mandatory file locking,
the distinction between advisory and mandatory locking is subtle. In
fact, advisory and mandatory record locks are exactly the same in so
far as the APIs and requirements on implementation. If the mandatory
lock attribute is set on the file, the server checks to see if the
lockowner has an appropriate shared (read) or exclusive (write)
record lock on the region it wishes to read or write to. If there is
no appropriate lock, the server checks if there is a conflicting lock
(which can be done by attempting to acquire the conflicting lock on
the behalf of the lockowner, and if successful, release the lock
after the READ or WRITE is done), and if there is, the server returns
NFS4ERR_LOCKED.
For Windows environments, there are no advisory record locks, so the
server always checks for record locks during I/O requests.
Thus, the NFS version 4 LOCK operation does not need to distinguish
between advisory and mandatory record locks. It is the NFS version 4
server's processing of the READ and WRITE operations that introduces
the distinction.
Every stateid other than the special stateid values noted in this
section, whether returned by an OPEN-type operation (i.e., OPEN,
OPEN_DOWNGRADE), or by a LOCK-type operation (i.e., LOCK or LOCKU),
defines an access mode for the file (i.e., READ, WRITE, or READ-
WRITE) as established by the original OPEN which began the stateid
sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
within that stateid sequence. When a READ, WRITE, or SETATTR which
specifies the size attribute, is done, the operation is subject to
checking against the access mode to verify that the operation is
appropriate given the OPEN with which the operation is associated.
In the case of WRITE-type operations (i.e., WRITEs and SETATTRs which
set size), the server must verify that the access mode allows writing
and return an NFS4ERR_OPENMODE error if it does not. In the case, of
READ, the server may perform the corresponding check on the access
mode, or it may choose to allow READ on opens for WRITE only, to
accommodate clients whose write implementation may unavoidably do
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reads (e.g., due to buffer cache constraints). However, even if
READs are allowed in these circumstances, the server MUST still check
for locks that conflict with the READ (e.g., another open specify
denial of READs). Note that a server which does enforce the access
mode check on READs need not explicitly check for conflicting share
reservations since the existence of OPEN for read access guarantees
that no conflicting share reservation can exist.
A stateid of all bits 1 (one) MAY allow READ operations to bypass
locking checks at the server. However, WRITE operations with a
stateid with bits all 1 (one) MUST NOT bypass locking checks and are
treated exactly the same as if a stateid of all bits 0 were used.
A lock may not be granted while a READ or WRITE operation using one
of the special stateids is being performed and the range of the lock
request conflicts with the range of the READ or WRITE operation. For
the purposes of this paragraph, a conflict occurs when a shared lock
is requested and a WRITE operation is being performed, or an
exclusive lock is requested and either a READ or a WRITE operation is
being performed. A SETATTR that sets size is treated similarly to a
WRITE as discussed above.
Locking is different than most NFS operations as it requires "at-
most-one" semantics that are not provided by ONCRPC. ONCRPC over a
reliable transport is not sufficient because a sequence of locking
requests may span multiple TCP connections. In the face of
retransmission or reordering, lock or unlock requests must have a
well defined and consistent behavior. To accomplish this, each lock
request contains a sequence number that is a consecutively increasing
integer. Different lock_owners have different sequences. The server
maintains the last sequence number (L) received and the response that
was returned. The first request issued for any given lock_owner is
issued with a sequence number of zero.
Note that for requests that contain a sequence number, for each
lock_owner, there should be no more than one outstanding request.
If a request (r) with a previous sequence number (r < L) is received,
it is rejected with the return of error NFS4ERR_BAD_SEQID. Given a
properly-functioning client, the response to (r) must have been
received before the last request (L) was sent. If a duplicate of
last request (r == L) is received, the stored response is returned.
If a request beyond the next sequence (r == L + 2) is received, it is
rejected with the return of error NFS4ERR_BAD_SEQID. Sequence
history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
sequence changes the client verifier.
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Since the sequence number is represented with an unsigned 32-bit
integer, the arithmetic involved with the sequence number is mod
2^32. For an example of modulo arithmetic involving sequence numbers
see [RFC793].
It is critical the server maintain the last response sent to the
client to provide a more reliable cache of duplicate non-idempotent
requests than that of the traditional cache described in [Juszczak].
The traditional duplicate request cache uses a least recently used
algorithm for removing unneeded requests. However, the last lock
request and response on a given lock_owner must be cached as long as
the lock state exists on the server.
The client MUST monotonically increment the sequence number for the
CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
operations. This is true even in the event that the previous
operation that used the sequence number received an error. The only
exception to this rule is if the previous operation received one of
the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.
As described above, the sequence number is per lock_owner. As long
as the server maintains the last sequence number received and follows
the methods described above, there are no risks of a Byzantine router
re-sending old requests. The server need only maintain the
(lock_owner, sequence number) state as long as there are open files
or closed files with locks outstanding.
LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
number and therefore the risk of the replay of these operations
resulting in undesired effects is non-existent while the server
maintains the lock_owner state.
When a particular lock_owner no longer holds open or file locking
state at the server, the server may choose to release the sequence
number state associated with the lock_owner. The server may make
this choice based on lease expiration, for the reclamation of server
memory, or other implementation specific details. In any event, the
server is able to do this safely only when the lock_owner no longer
is being utilized by the client. The server may choose to hold the
lock_owner state in the event that retransmitted requests are
received. However, the period to hold this state is implementation
specific.
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In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
retransmitted after the server has previously released the lock_owner
state, the server will find that the lock_owner has no files open and
an error will be returned to the client. If the lock_owner does have
a file open, the stateid will not match and again an error is
returned to the client.
In the case that an OPEN is retransmitted and the lock_owner is being
used for the first time or the lock_owner state has been previously
released by the server, the use of the OPEN_CONFIRM operation will
prevent incorrect behavior. When the server observes the use of the
lock_owner for the first time, it will direct the client to perform
the OPEN_CONFIRM for the corresponding OPEN. This sequence
establishes the use of an lock_owner and associated sequence number.
Since the OPEN_CONFIRM sequence connects a new open_owner on the
server with an existing open_owner on a client, the sequence number
may have any value. The OPEN_CONFIRM step assures the server that
the value received is the correct one. See the section "OPEN_CONFIRM
- Confirm Open" for further details.
There are a number of situations in which the requirement to confirm
an OPEN would pose difficulties for the client and server, in that
they would be prevented from acting in a timely fashion on
information received, because that information would be provisional,
subject to deletion upon non-confirmation. Fortunately, these are
situations in which the server can avoid the need for confirmation
when responding to open requests. The two constraints are:
o The server must not bestow a delegation for any open which would
require confirmation.
o The server MUST NOT require confirmation on a reclaim-type open
(i.e., one specifying claim type CLAIM_PREVIOUS or
CLAIM_DELEGATE_PREV).
These constraints are related in that reclaim-type opens are the only
ones in which the server may be required to send a delegation. For
CLAIM_NULL, sending the delegation is optional while for
CLAIM_DELEGATE_CUR, no delegation is sent.
Delegations being sent with an open requiring confirmation are
troublesome because recovering from non-confirmation adds undue
complexity to the protocol while requiring confirmation on reclaim-
type opens poses difficulties in that the inability to resolve
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the status of the reclaim until lease expiration may make it
difficult to have timely determination of the set of locks being
reclaimed (since the grace period may expire).
Requiring open confirmation on reclaim-type opens is avoidable
because of the nature of the environments in which such opens are
done. For CLAIM_PREVIOUS opens, this is immediately after server
reboot, so there should be no time for lockowners to be created,
found to be unused, and recycled. For CLAIM_DELEGATE_PREV opens, we
are dealing with a client reboot situation. A server which supports
delegation can be sure that no lockowners for that client have been
recycled since client initialization and thus can ensure that
confirmation will not be required.
The protocol allows a lock owner to request a lock with a byte range
and then either upgrade or unlock a sub-range of the initial lock.
It is expected that this will be an uncommon type of request. In any
case, servers or server filesystems may not be able to support sub-
range lock semantics. In the event that a server receives a locking
request that represents a sub-range of current locking state for the
lock owner, the server is allowed to return the error
NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
operations. Therefore, the client should be prepared to receive this
error and, if appropriate, report the error to the requesting
application.
The client is discouraged from combining multiple independent locking
ranges that happen to be adjacent into a single request since the
server may not support sub-range requests and for reasons related to
the recovery of file locking state in the event of server failure.
As discussed in the section "Server Failure and Recovery" below, the
server may employ certain optimizations during recovery that work
effectively only when the client's behavior during lock recovery is
similar to the client's locking behavior prior to server failure.
If a client has a write lock on a record, it can request an atomic
downgrade of the lock to a read lock via the LOCK request, by setting
the type to READ_LT. If the server supports atomic downgrade, the
request will succeed. If not, it will return NFS4ERR_LOCK_NOTSUPP.
The client should be prepared to receive this error, and if
appropriate, report the error to the requesting application.
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If a client has a read lock on a record, it can request an atomic
upgrade of the lock to a write lock via the LOCK request by setting
the type to WRITE_LT or WRITEW_LT. If the server does not support
atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP. If the upgrade
can be achieved without an existing conflict, the request will
succeed. Otherwise, the server will return either NFS4ERR_DENIED or
NFS4ERR_DEADLOCK. The error NFS4ERR_DEADLOCK is returned if the
client issued the LOCK request with the type set to WRITEW_LT and the
server has detected a deadlock. The client should be prepared to
receive such errors and if appropriate, report the error to the
requesting application.
Some clients require the support of blocking locks. The NFS version
4 protocol must not rely on a callback mechanism and therefore is
unable to notify a client when a previously denied lock has been
granted. Clients have no choice but to continually poll for the
lock. This presents a fairness problem. Two new lock types are
added, READW and WRITEW, and are used to indicate to the server that
the client is requesting a blocking lock. The server should maintain
an ordered list of pending blocking locks. When the conflicting lock
is released, the server may wait the lease period for the first
waiting client to re-request the lock. After the lease period
expires the next waiting client request is allowed the lock. Clients
are required to poll at an interval sufficiently small that it is
likely to acquire the lock in a timely manner. The server is not
required to maintain a list of pending blocked locks as it is used to
increase fairness and not correct operation. Because of the
unordered nature of crash recovery, storing of lock state to stable
storage would be required to guarantee ordered granting of blocking
locks.
Servers may also note the lock types and delay returning denial of
the request to allow extra time for a conflicting lock to be
released, allowing a successful return. In this way, clients can
avoid the burden of needlessly frequent polling for blocking locks.
The server should take care in the length of delay in the event the
client retransmits the request.
The purpose of a lease is to allow a server to remove stale locks
that are held by a client that has crashed or is otherwise
unreachable. It is not a mechanism for cache consistency and lease
renewals may not be denied if the lease interval has not expired.
Shepler, et al. Standards Track [Page 77]
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The following events cause implicit renewal of all of the leases for
a given client (i.e., all those sharing a given clientid). Each of
these is a positive indication that the client is still active and
that the associated state held at the server, for the client, is
still valid.
o An OPEN with a valid clientid.
o Any operation made with a valid stateid (CLOSE, DELEGPURGE,
DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE,
READ, RENEW, SETATTR, WRITE). This does not include the special
stateids of all bits 0 or all bits 1.
Note that if the client had restarted or rebooted, the client
would not be making these requests without issuing the
SETCLIENTID/SETCLIENTID_CONFIRM sequence. The use of the
SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
client verifier) notifies the server to drop the locking state
associated with the client. SETCLIENTID/SETCLIENTID_CONFIRM never
renews a lease.
If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not be
valid hence preventing spurious renewals.
This approach allows for low overhead lease renewal which scales
well. In the typical case no extra RPC calls are required for lease
renewal and in the worst case one RPC is required every lease period
(i.e., a RENEW operation). The number of locks held by the client is
not a factor since all state for the client is involved with the
lease renewal action.
Since all operations that create a new lease also renew existing
leases, the server must maintain a common lease expiration time for
all valid leases for a given client. This lease time can then be
easily updated upon implicit lease renewal actions.
The important requirement in crash recovery is that both the client
and the server know when the other has failed. Additionally, it is
required that a client sees a consistent view of data across server
restarts or reboots. All READ and WRITE operations that may have
been queued within the client or network buffers must wait until the
client has successfully recovered the locks protecting the READ and
WRITE operations.
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In the event that a client fails, the server may recover the client's
locks when the associated leases have expired. Conflicting locks
from another client may only be granted after this lease expiration.
If the client is able to restart or reinitialize within the lease
period the client may be forced to wait the remainder of the lease
period before obtaining new locks.
To minimize client delay upon restart, lock requests are associated
with an instance of the client by a client supplied verifier. This
verifier is part of the initial SETCLIENTID call made by the client.
The server returns a clientid as a result of the SETCLIENTID
operation. The client then confirms the use of the clientid with
SETCLIENTID_CONFIRM. The clientid in combination with an opaque
owner field is then used by the client to identify the lock owner for
OPEN. This chain of associations is then used to identify all locks
for a particular client.
Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the verifier
associated with currently held locks and determine that they do not
match. This signifies the client's new instantiation and subsequent
loss of locking state. As a result, the server is free to release
all locks held which are associated with the old clientid which was
derived from the old verifier.
Note that the verifier must have the same uniqueness properties of
the verifier for the COMMIT operation.
If the server loses locking state (usually as a result of a restart
or reboot), it must allow clients time to discover this fact and re-
establish the lost locking state. The client must be able to re-
establish the locking state without having the server deny valid
requests because the server has granted conflicting access to another
client. Likewise, if there is the possibility that clients have not
yet re-established their locking state for a file, the server must
disallow READ and WRITE operations for that file. The duration of
this recovery period is equal to the duration of the lease period.
A client can determine that server failure (and thus loss of locking
state) has occurred, when it receives one of two errors. The
NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
reboot or restart. The NFS4ERR_STALE_CLIENTID error indicates a
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clientid invalidated by reboot or restart. When either of these are
received, the client must establish a new clientid (See the section
"Client ID") and re-establish the locking state as discussed below.
The period of special handling of locking and READs and WRITEs, equal
in duration to the lease period, is referred to as the "grace
period". During the grace period, clients recover locks and the
associated state by reclaim-type locking requests (i.e., LOCK
requests with reclaim set to true and OPEN operations with a claim
type of CLAIM_PREVIOUS). During the grace period, the server must
reject READ and WRITE operations and non-reclaim locking requests
(i.e., other LOCK and OPEN operations) with an error of
NFS4ERR_GRACE.
If the server can reliably determine that granting a non-reclaim
request will not conflict with reclamation of locks by other clients,
the NFS4ERR_GRACE error does not have to be returned and the non-
reclaim client request can be serviced. For the server to be able to
service READ and WRITE operations during the grace period, it must
again be able to guarantee that no possible conflict could arise
between an impending reclaim locking request and the READ or WRITE
operation. If the server is unable to offer that guarantee, the
NFS4ERR_GRACE error must be returned to the client.
For a server to provide simple, valid handling during the grace
period, the easiest method is to simply reject all non-reclaim
locking requests and READ and WRITE operations by returning the
NFS4ERR_GRACE error. However, a server may keep information about
granted locks in stable storage. With this information, the server
could determine if a regular lock or READ or WRITE operation can be
safely processed.
For example, if a count of locks on a given file is available in
stable storage, the server can track reclaimed locks for the file and
when all reclaims have been processed, non-reclaim locking requests
may be processed. This way the server can ensure that non-reclaim
locking requests will not conflict with potential reclaim requests.
With respect to I/O requests, if the server is able to determine that
there are no outstanding reclaim requests for a file by information
from stable storage or another similar mechanism, the processing of
I/O requests could proceed normally for the file.
To reiterate, for a server that allows non-reclaim lock and I/O
requests to be processed during the grace period, it MUST determine
that no lock subsequently reclaimed will be rejected and that no lock
subsequently reclaimed would have prevented any I/O operation
processed during the grace period.
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Clients should be prepared for the return of NFS4ERR_GRACE errors for
non-reclaim lock and I/O requests. In this case the client should
employ a retry mechanism for the request. A delay (on the order of
several seconds) between retries should be used to avoid overwhelming
the server. Further discussion of the general issue is included in
[Floyd]. The client must account for the server that is able to
perform I/O and non-reclaim locking requests within the grace period
as well as those that can not do so.
A reclaim-type locking request outside the server's grace period can
only succeed if the server can guarantee that no conflicting lock or
I/O request has been granted since reboot or restart.
A server may, upon restart, establish a new value for the lease
period. Therefore, clients should, once a new clientid is
established, refetch the lease_time attribute and use it as the basis
for lease renewal for the lease associated with that server.
However, the server must establish, for this restart event, a grace
period at least as long as the lease period for the previous server
instantiation. This allows the client state obtained during the
previous server instance to be reliably re-established.
If the duration of a network partition is greater than the lease
period provided by the server, the server will have not received a
lease renewal from the client. If this occurs, the server may free
all locks held for the client. As a result, all stateids held by the
client will become invalid or stale. Once the client is able to
reach the server after such a network partition, all I/O submitted by
the client with the now invalid stateids will fail with the server
returning the error NFS4ERR_EXPIRED. Once this error is received,
the client will suitably notify the application that held the lock.
As a courtesy to the client or as an optimization, the server may
continue to hold locks on behalf of a client for which recent
communication has extended beyond the lease period. If the server
receives a lock or I/O request that conflicts with one of these
courtesy locks, the server must free the courtesy lock and grant the
new request.
When a network partition is combined with a server reboot, there are
edge conditions that place requirements on the server in order to
avoid silent data corruption following the server reboot. Two of
these edge conditions are known, and are discussed below.
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The first edge condition has the following scenario:
1. Client A acquires a lock.
2. Client A and server experience mutual network partition, such
that client A is unable to renew its lease.
3. Client A's lease expires, so server releases lock.
4. Client B acquires a lock that would have conflicted with that
of Client A.
5. Client B releases the lock
6. Server reboots
7. Network partition between client A and server heals.
8. Client A issues a RENEW operation, and gets back a
NFS4ERR_STALE_CLIENTID.
9. Client A reclaims its lock within the server's grace period.
Thus, at the final step, the server has erroneously granted client
A's lock reclaim. If client B modified the object the lock was
protecting, client A will experience object corruption.
The second known edge condition follows:
1. Client A acquires a lock.
2. Server reboots.
3. Client A and server experience mutual network partition, such
that client A is unable to reclaim its lock within the grace
period.
4. Server's reclaim grace period ends. Client A has no locks
recorded on server.
5. Client B acquires a lock that would have conflicted with that
of Client A.
6. Client B releases the lock.
7. Server reboots a second time.
8. Network partition between client A and server heals.
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9. Client A issues a RENEW operation, and gets back a
NFS4ERR_STALE_CLIENTID.
10. Client A reclaims its lock within the server's grace period.
As with the first edge condition, the final step of the scenario of
the second edge condition has the server erroneously granting client
A's lock reclaim.
Solving the first and second edge conditions requires that the server
either assume after it reboots that edge condition occurs, and thus
return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
record some information stable storage. The amount of information
the server records in stable storage is in inverse proportion to how
harsh the server wants to be whenever the edge conditions occur. The
server that is completely tolerant of all edge conditions will record
in stable storage every lock that is acquired, removing the lock
record from stable storage only when the lock is unlocked by the
client and the lock's lockowner advances the sequence number such
that the lock release is not the last stateful event for the
lockowner's sequence. For the two aforementioned edge conditions,
the harshest a server can be, and still support a grace period for
reclaims, requires that the server record in stable storage
information some minimal information. For example, a server
implementation could, for each client, save in stable storage a
record containing:
o the client's id string
o a boolean that indicates if the client's lease expired or if there
was administrative intervention (see the section, Server
Revocation of Locks) to revoke a record lock, share reservation,
or delegation
o a timestamp that is updated the first time after a server boot or
reboot the client acquires record locking, share reservation, or
delegation state on the server. The timestamp need not be updated
on subsequent lock requests until the server reboots.
The server implementation would also record in the stable storage the
timestamps from the two most recent server reboots.
Assuming the above record keeping, for the first edge condition,
after the server reboots, the record that client A's lease expired
means that another client could have acquired a conflicting record
lock, share reservation, or delegation. Hence the server must reject
a reclaim from client A with the error NFS4ERR_NO_GRACE.
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For the second edge condition, after the server reboots for a second
time, the record that the client had an unexpired record lock, share
reservation, or delegation established before the server's previous
incarnation means that the server must reject a reclaim from client A
with the error NFS4ERR_NO_GRACE.
Regardless of the level and approach to record keeping, the server
MUST implement one of the following strategies (which apply to
reclaims of share reservations, record locks, and delegations):
1. Reject all reclaims with NFS4ERR_NO_GRACE. This is superharsh,
but necessary if the server does not want to record lock state
in stable storage.
2. Record sufficient state in stable storage such that all known
edge conditions involving server reboot, including the two
noted in this section, are detected. False positives are
acceptable. Note that at this time, it is not known if there
are other edge conditions.
In the event, after a server reboot, the server determines that
there is unrecoverable damage or corruption to the the stable
storage, then for all clients and/or locks affected, the server
MUST return NFS4ERR_NO_GRACE.
A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
outside the scope of this specification, since the strategies for
such handling are very dependent on the client's operating
environment. However, one potential approach is described below.
When the client receives NFS4ERR_NO_GRACE, it could examine the
change attribute of the objects the client is trying to reclaim state
for, and use that to determine whether to re-establish the state via
normal OPEN or LOCK requests. This is acceptable provided the
client's operating environment allows it. In otherwords, the client
implementor is advised to document for his users the behavior. The
client could also inform the application that its record lock or
share reservations (whether they were delegated or not) have been
lost, such as via a UNIX signal, a GUI pop-up window, etc. See the
section, "Data Caching and Revocation" for a discussion of what the
client should do for dealing with unreclaimed delegations on client
state.
For further discussion of revocation of locks see the section "Server
Revocation of Locks".
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In the event a lock request times out, a client may decide to not
retry the request. The client may also abort the request when the
process for which it was issued is terminated (e.g., in UNIX due to a
signal). It is possible though that the server received the request
and acted upon it. This would change the state on the server without
the client being aware of the change. It is paramount that the
client re-synchronize state with server before it attempts any other
operation that takes a seqid and/or a stateid with the same
lock_owner. This is straightforward to do without a special re-
synchronize operation.
Since the server maintains the last lock request and response
received on the lock_owner, for each lock_owner, the client should
cache the last lock request it sent such that the lock request did
not receive a response. From this, the next time the client does a
lock operation for the lock_owner, it can send the cached request, if
there is one, and if the request was one that established state
(e.g., a LOCK or OPEN operation), the server will return the cached
result or if never saw the request, perform it. The client can
follow up with a request to remove the state (e.g., a LOCKU or CLOSE
operation). With this approach, the sequencing and stateid
information on the client and server for the given lock_owner will
re-synchronize and in turn the lock state will re-synchronize.
At any point, the server can revoke locks held by a client and the
client must be prepared for this event. When the client detects that
its locks have been or may have been revoked, the client is
responsible for validating the state information between itself and
the server. Validating locking state for the client means that it
must verify or reclaim state for each lock currently held.
The first instance of lock revocation is upon server reboot or re-
initialization. In this instance the client will receive an error
(NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
proceed with normal crash recovery as described in the previous
section.
The second lock revocation event is the inability to renew the lease
before expiration. While this is considered a rare or unusual event,
the client must be prepared to recover. Both the server and client
will be able to detect the failure to renew the lease and are capable
of recovering without data corruption. For the server, it tracks the
last renewal event serviced for the client and knows when the lease
will expire. Similarly, the client must track operations which will
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renew the lease period. Using the time that each such request was
sent and the time that the corresponding reply was received, the
client should bound the time that the corresponding renewal could
have occurred on the server and thus determine if it is possible that
a lease period expiration could have occurred.
The third lock revocation event can occur as a result of
administrative intervention within the lease period. While this is
considered a rare event, it is possible that the server's
administrator has decided to release or revoke a particular lock held
by the client. As a result of revocation, the client will receive an
error of NFS4ERR_ADMIN_REVOKED. In this instance the client may
assume that only the lock_owner's locks have been lost. The client
notifies the lock holder appropriately. The client may not assume
the lease period has been renewed as a result of failed operation.
When the client determines the lease period may have expired, the
client must mark all locks held for the associated lease as
"unvalidated". This means the client has been unable to re-establish
or confirm the appropriate lock state with the server. As described
in the previous section on crash recovery, there are scenarios in
which the server may grant conflicting locks after the lease period
has expired for a client. When it is possible that the lease period
has expired, the client must validate each lock currently held to
ensure that a conflicting lock has not been granted. The client may
accomplish this task by issuing an I/O request, either a pending I/O
or a zero-length read, specifying the stateid associated with the
lock in question. If the response to the request is success, the
client has validated all of the locks governed by that stateid and
re-established the appropriate state between itself and the server.
If the I/O request is not successful, then one or more of the locks
associated with the stateid was revoked by the server and the client
must notify the owner.
A share reservation is a mechanism to control access to a file. It
is a separate and independent mechanism from record locking. When a
client opens a file, it issues an OPEN operation to the server
specifying the type of access required (READ, WRITE, or BOTH) and the
type of access to deny others (deny NONE, READ, WRITE, or BOTH). If
the OPEN fails the client will fail the application's open request.
Pseudo-code definition of the semantics:
if (request.access == 0)
return (NFS4ERR_INVAL)
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else
if ((request.access & file_state.deny)) ||
(request.deny & file_state.access))
return (NFS4ERR_DENIED)
This checking of share reservations on OPEN is done with no exception
for an existing OPEN for the same open_owner.
The constants used for the OPEN and OPEN_DOWNGRADE operations for the
access and deny fields are as follows:
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
To provide correct share semantics, a client MUST use the OPEN
operation to obtain the initial filehandle and indicate the desired
access and what if any access to deny. Even if the client intends to
use a stateid of all 0's or all 1's, it must still obtain the
filehandle for the regular file with the OPEN operation so the
appropriate share semantics can be applied. For clients that do not
have a deny mode built into their open programming interfaces, deny
equal to NONE should be used.
The OPEN operation with the CREATE flag, also subsumes the CREATE
operation for regular files as used in previous versions of the NFS
protocol. This allows a create with a share to be done atomically.
The CLOSE operation removes all share reservations held by the
lock_owner on that file. If record locks are held, the client SHOULD
release all locks before issuing a CLOSE. The server MAY free all
outstanding locks on CLOSE but some servers may not support the CLOSE
of a file that still has record locks held. The server MUST return
failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
CLOSE.
The LOOKUP operation will return a filehandle without establishing
any lock state on the server. Without a valid stateid, the server
will assume the client has the least access. For example, a file
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opened with deny READ/WRITE cannot be accessed using a filehandle
obtained through LOOKUP because it would not have a valid stateid
(i.e., using a stateid of all bits 0 or all bits 1).
Since a CLOSE operation requests deallocation of a stateid, dealing
with retransmission of the CLOSE, may pose special difficulties,
since the state information, which normally would be used to
determine the state of the open file being designated, might be
deallocated, resulting in an NFS4ERR_BAD_STATEID error.
Servers may deal with this problem in a number of ways. To provide
the greatest degree assurance that the protocol is being used
properly, a server should, rather than deallocate the stateid, mark
it as close-pending, and retain the stateid with this status, until
later deallocation. In this way, a retransmitted CLOSE can be
recognized since the stateid points to state information with this
distinctive status, so that it can be handled without error.
When adopting this strategy, a server should retain the state
information until the earliest of:
o Another validly sequenced request for the same lockowner, that is
not a retransmission.
o The time that a lockowner is freed by the server due to period
with no activity.
o All locks for the client are freed as a result of a SETCLIENTID.
Servers may avoid this complexity, at the cost of less complete
protocol error checking, by simply responding NFS4_OK in the event of
a CLOSE for a deallocated stateid, on the assumption that this case
must be caused by a retransmitted close. When adopting this
approach, it is desirable to at least log an error when returning a
no-error indication in this situation. If the server maintains a
reply-cache mechanism, it can verify the CLOSE is indeed a
retransmission and avoid error logging in most cases.
When an OPEN is done for a file and the lockowner for which the open
is being done already has the file open, the result is to upgrade the
open file status maintained on the server to include the access and
deny bits specified by the new OPEN as well as those for the existing
OPEN. The result is that there is one open file, as far as the
protocol is concerned, and it includes the union of the access and
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deny bits for all of the OPEN requests completed. Only a single
CLOSE will be done to reset the effects of both OPENs. Note that the
client, when issuing the OPEN, may not know that the same file is in
fact being opened. The above only applies if both OPENs result in
the OPENed object being designated by the same filehandle.
When the server chooses to export multiple filehandles corresponding
to the same file object and returns different filehandles on two
different OPENs of the same file object, the server MUST NOT "OR"
together the access and deny bits and coalesce the two open files.
Instead the server must maintain separate OPENs with separate
stateids and will require separate CLOSEs to free them.
When multiple open files on the client are merged into a single open
file object on the server, the close of one of the open files (on the
client) may necessitate change of the access and deny status of the
open file on the server. This is because the union of the access and
deny bits for the remaining opens may be smaller (i.e., a proper
subset) than previously. The OPEN_DOWNGRADE operation is used to
make the necessary change and the client should use it to update the
server so that share reservation requests by other clients are
handled properly.
When determining the time period for the server lease, the usual
lease tradeoffs apply. Short leases are good for fast server
recovery at a cost of increased RENEW or READ (with zero length)
requests. Longer leases are certainly kinder and gentler to servers
trying to handle very large numbers of clients. The number of RENEW
requests drop in proportion to the lease time. The disadvantages of
long leases are slower recovery after server failure (the server must
wait for the leases to expire and the grace period to elapse before
granting new lock requests) and increased file contention (if client
fails to transmit an unlock request then server must wait for lease
expiration before granting new locks).
Long leases are usable if the server is able to store lease state in
non-volatile memory. Upon recovery, the server can reconstruct the
lease state from its non-volatile memory and continue operation with
its clients and therefore long leases would not be an issue.
To avoid the need for synchronized clocks, lease times are granted by
the server as a time delta. However, there is a requirement that the
client and server clocks do not drift excessively over the duration
of the lock. There is also the issue of propagation delay across the
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network which could easily be several hundred milliseconds as well as
the possibility that requests will be lost and need to be
retransmitted.
To take propagation delay into account, the client should subtract it
from lease times (e.g., if the client estimates the one-way
propagation delay as 200 msec, then it can assume that the lease is
already 200 msec old when it gets it). In addition, it will take
another 200 msec to get a response back to the server. So the client
must send a lock renewal or write data back to the server 400 msec
before the lease would expire.
The server's lease period configuration should take into account the
network distance of the clients that will be accessing the server's
resources. It is expected that the lease period will take into
account the network propagation delays and other network delay
factors for the client population. Since the protocol does not allow
for an automatic method to determine an appropriate lease period, the
server's administrator may have to tune the lease period.
When responsibility for handling a given file system is transferred
to a new server (migration) or the client chooses to use an alternate
server (e.g., in response to server unresponsiveness) in the context
of file system replication, the appropriate handling of state shared
between the client and server (i.e., locks, leases, stateids, and
clientids) is as described below. The handling differs between
migration and replication. For related discussion of file server
state and recover of such see the sections under "File Locking and
Share Reservations".
If server replica or a server immigrating a filesystem agrees to, or
is expected to, accept opaque values from the client that originated
from another server, then it is a wise implementation practice for
the servers to encode the "opaque" values in network byte order.
This way, servers acting as replicas or immigrating filesystems will
be able to parse values like stateids, directory cookies,
filehandles, etc. even if their native byte order is different from
other servers cooperating in the replication and migration of the
filesystem.
In the case of migration, the servers involved in the migration of a
filesystem SHOULD transfer all server state from the original to the
new server. This must be done in a way that is transparent to the
client. This state transfer will ease the client's transition when a
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filesystem migration occurs. If the servers are successful in
transferring all state, the client will continue to use stateids
assigned by the original server. Therefore the new server must
recognize these stateids as valid. This holds true for the clientid
as well. Since responsibility for an entire filesystem is
transferred with a migration event, there is no possibility that
conflicts will arise on the new server as a result of the transfer of
locks.
As part of the transfer of information between servers, leases would
be transferred as well. The leases being transferred to the new
server will typically have a different expiration time from those for
the same client, previously on the old server. To maintain the
property that all leases on a given server for a given client expire
at the same time, the server should advance the expiration time to
the later of the leases being transferred or the leases already
present. This allows the client to maintain lease renewal of both
classes without special effort.
The servers may choose not to transfer the state information upon
migration. However, this choice is discouraged. In this case, when
the client presents state information from the original server, the
client must be prepared to receive either NFS4ERR_STALE_CLIENTID or
NFS4ERR_STALE_STATEID from the new server. The client should then
recover its state information as it normally would in response to a
server failure. The new server must take care to allow for the
recovery of state information as it would in the event of server
restart.
Since client switch-over in the case of replication is not under
server control, the handling of state is different. In this case,
leases, stateids and clientids do not have validity across a
transition from one server to another. The client must re-establish
its locks on the new server. This can be compared to the re-
establishment of locks by means of reclaim-type requests after a
server reboot. The difference is that the server has no provision to
distinguish requests reclaiming locks from those obtaining new locks
or to defer the latter. Thus, a client re-establishing a lock on the
new server (by means of a LOCK or OPEN request), may have the
requests denied due to a conflicting lock. Since replication is
intended for read-only use of filesystems, such denial of locks
should not pose large difficulties in practice. When an attempt to
re-establish a lock on a new server is denied, the client should
treat the situation as if his original lock had been revoked.
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In the case of lease renewal, the client may not be submitting
requests for a filesystem that has been migrated to another server.
This can occur because of the implicit lease renewal mechanism. The
client renews leases for all filesystems when submitting a request to
any one filesystem at the server.
In order for the client to schedule renewal of leases that may have
been relocated to the new server, the client must find out about
lease relocation before those leases expire. To accomplish this, all
operations which implicitly renew leases for a client (i.e., OPEN,
CLOSE, READ, WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
renewed has been transferred to a new server. This condition will
continue until the client receives an NFS4ERR_MOVED error and the
server receives the subsequent GETATTR(fs_locations) for an access to
each filesystem for which a lease has been moved to a new server.
When a client receives an NFS4ERR_LEASE_MOVED error, it should
perform an operation on each filesystem associated with the server in
question. When the client receives an NFS4ERR_MOVED error, the
client can follow the normal process to obtain the new server
information (through the fs_locations attribute) and perform renewal
of those leases on the new server. If the server has not had state
transferred to it transparently, the client will receive either
NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
as described above, and the client can then recover state information
as it does in the event of server failure.
In order that the client may appropriately manage its leases in the
case of migration, the destination server must establish proper
values for the lease_time attribute.
When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time
attribute on the destination server must never be less than that on
the source since this would result in premature expiration of leases
granted by the source server. Upon migration in which state is
transferred transparently, the client is under no obligation to re-
fetch the lease_time attribute and may continue to use the value
previously fetched (on the source server).
If state has not been transferred transparently (i.e., the client
sees a real or simulated server reboot), the client should fetch the
value of lease_time on the new (i.e., destination) server, and use it
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for subsequent locking requests. However the server must respect a
grace period at least as long as the lease_time on the source server,
in order to ensure that clients have ample time to reclaim their
locks before potentially conflicting non-reclaimed locks are granted.
The means by which the new server obtains the value of lease_time on
the old server is left to the server implementations. It is not
specified by the NFS version 4 protocol.
Client-side caching of data, of file attributes, and of file names is
essential to providing good performance with the NFS protocol.
Providing distributed cache coherence is a difficult problem and
previous versions of the NFS protocol have not attempted it.
Instead, several NFS client implementation techniques have been used
to reduce the problems that a lack of coherence poses for users.
These techniques have not been clearly defined by earlier protocol
specifications and it is often unclear what is valid or invalid
client behavior.
The NFS version 4 protocol uses many techniques similar to those that
have been used in previous protocol versions. The NFS version 4
protocol does not provide distributed cache coherence. However, it
defines a more limited set of caching guarantees to allow locks and
share reservations to be used without destructive interference from
client side caching.
In addition, the NFS version 4 protocol introduces a delegation
mechanism which allows many decisions normally made by the server to
be made locally by clients. This mechanism provides efficient
support of the common cases where sharing is infrequent or where
sharing is read-only.
Caching techniques used in previous versions of the NFS protocol have
been successful in providing good performance. However, several
scalability challenges can arise when those techniques are used with
very large numbers of clients. This is particularly true when
clients are geographically distributed which classically increases
the latency for cache revalidation requests.
The previous versions of the NFS protocol repeat their file data
cache validation requests at the time the file is opened. This
behavior can have serious performance drawbacks. A common case is
one in which a file is only accessed by a single client. Therefore,
sharing is infrequent.
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In this case, repeated reference to the server to find that no
conflicts exist is expensive. A better option with regards to
performance is to allow a client that repeatedly opens a file to do
so without reference to the server. This is done until potentially
conflicting operations from another client actually occur.
A similar situation arises in connection with file locking. Sending
file lock and unlock requests to the server as well as the read and
write requests necessary to make data caching consistent with the
locking semantics (see the section "Data Caching and File Locking")
can severely limit performance. When locking is used to provide
protection against infrequent conflicts, a large penalty is incurred.
This penalty may discourage the use of file locking by applications.
The NFS version 4 protocol provides more aggressive caching
strategies with the following design goals:
o Compatibility with a large range of server semantics.
o Provide the same caching benefits as previous versions of the NFS
protocol when unable to provide the more aggressive model.
o Requirements for aggressive caching are organized so that a large
portion of the benefit can be obtained even when not all of the
requirements can be met.
The appropriate requirements for the server are discussed in later
sections in which specific forms of caching are covered. (see the
section "Open Delegation").
Recallable delegation of server responsibilities for a file to a
client improves performance by avoiding repeated requests to the
server in the absence of inter-client conflict. With the use of a
"callback" RPC from server to client, a server recalls delegated
responsibilities when another client engages in sharing of a
delegated file.
A delegation is passed from the server to the client, specifying the
object of the delegation and the type of delegation. There are
different types of delegations but each type contains a stateid to be
used to represent the delegation when performing operations that
depend on the delegation. This stateid is similar to those
associated with locks and share reservations but differs in that the
stateid for a delegation is associated with a clientid and may be
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used on behalf of all the open_owners for the given client. A
delegation is made to the client as a whole and not to any specific
process or thread of control within it.
Because callback RPCs may not work in all environments (due to
firewalls, for example), correct protocol operation does not depend
on them. Preliminary testing of callback functionality by means of a
CB_NULL procedure determines whether callbacks can be supported. The
CB_NULL procedure checks the continuity of the callback path. A
server makes a preliminary assessment of callback availability to a
given client and avoids delegating responsibilities until it has
determined that callbacks are supported. Because the granting of a
delegation is always conditional upon the absence of conflicting
access, clients must not assume that a delegation will be granted and
they must always be prepared for OPENs to be processed without any
delegations being granted.
Once granted, a delegation behaves in most ways like a lock. There
is an associated lease that is subject to renewal together with all
of the other leases held by that client.
Unlike locks, an operation by a second client to a delegated file
will cause the server to recall a delegation through a callback.
On recall, the client holding the delegation must flush modified
state (such as modified data) to the server and return the
delegation. The conflicting request will not receive a response
until the recall is complete. The recall is considered complete when
the client returns the delegation or the server times out on the
recall and revokes the delegation as a result of the timeout.
Following the resolution of the recall, the server has the
information necessary to grant or deny the second client's request.
At the time the client receives a delegation recall, it may have
substantial state that needs to be flushed to the server. Therefore,
the server should allow sufficient time for the delegation to be
returned since it may involve numerous RPCs to the server. If the
server is able to determine that the client is diligently flushing
state to the server as a result of the recall, the server may extend
the usual time allowed for a recall. However, the time allowed for
recall completion should not be unbounded.
An example of this is when responsibility to mediate opens on a given
file is delegated to a client (see the section "Open Delegation").
The server will not know what opens are in effect on the client.
Without this knowledge the server will be unable to determine if the
access and deny state for the file allows any particular open until
the delegation for the file has been returned.
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A client failure or a network partition can result in failure to
respond to a recall callback. In this case, the server will revoke
the delegation which in turn will render useless any modified state
still on the client.
There are three situations that delegation recovery must deal with:
o Client reboot or restart
o Server reboot or restart
o Network partition (full or callback-only)
In the event the client reboots or restarts, the failure to renew
leases will result in the revocation of record locks and share
reservations. Delegations, however, may be treated a bit
differently.
There will be situations in which delegations will need to be
reestablished after a client reboots or restarts. The reason for
this is the client may have file data stored locally and this data
was associated with the previously held delegations. The client will
need to reestablish the appropriate file state on the server.
To allow for this type of client recovery, the server MAY extend the
period for delegation recovery beyond the typical lease expiration
period. This implies that requests from other clients that conflict
with these delegations will need to wait. Because the normal recall
process may require significant time for the client to flush changed
state to the server, other clients need be prepared for delays that
occur because of a conflicting delegation. This longer interval
would increase the window for clients to reboot and consult stable
storage so that the delegations can be reclaimed. For open
delegations, such delegations are reclaimed using OPEN with a claim
type of CLAIM_DELEGATE_PREV. (See the sections on "Data Caching and
Revocation" and "Operation 18: OPEN" for discussion of open
delegation and the details of OPEN respectively).
A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and
instead MUST, for a period of time no less than that of the value of
the lease_time attribute, maintain the client's delegations to allow
time for the client to issue CLAIM_DELEGATE_PREV requests. The
server that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
operation.
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When the server reboots or restarts, delegations are reclaimed (using
the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
record locks and share reservations. However, there is a slight
semantic difference. In the normal case if the server decides that a
delegation should not be granted, it performs the requested action
(e.g., OPEN) without granting any delegation. For reclaim, the
server grants the delegation but a special designation is applied so
that the client treats the delegation as having been granted but
recalled by the server. Because of this, the client has the duty to
write all modified state to the server and then return the
delegation. This process of handling delegation reclaim reconciles
three principles of the NFS version 4 protocol:
o Upon reclaim, a client reporting resources assigned to it by an
earlier server instance must be granted those resources.
o The server has unquestionable authority to determine whether
delegations are to be granted and, once granted, whether they are
to be continued.
o The use of callbacks is not to be depended upon until the client
has proven its ability to receive them.
When a network partition occurs, delegations are subject to freeing
by the server when the lease renewal period expires. This is similar
to the behavior for locks and share reservations. For delegations,
however, the server may extend the period in which conflicting
requests are held off. Eventually the occurrence of a conflicting
request from another client will cause revocation of the delegation.
A loss of the callback path (e.g., by later network configuration
change) will have the same effect. A recall request will fail and
revocation of the delegation will result.
A client normally finds out about revocation of a delegation when it
uses a stateid associated with a delegation and receives the error
NFS4ERR_EXPIRED. It also may find out about delegation revocation
after a client reboot when it attempts to reclaim a delegation and
receives that same error. Note that in the case of a revoked write
open delegation, there are issues because data may have been modified
by the client whose delegation is revoked and separately by other
clients. See the section "Revocation Recovery for Write Open
Delegation" for a discussion of such issues. Note also that when
delegations are revoked, information about the revoked delegation
will be written by the server to stable storage (as described in the
section "Crash Recovery"). This is done to deal with the case in
which a server reboots after revoking a delegation but before the
client holding the revoked delegation is notified about the
revocation.
Shepler, et al. Standards Track [Page 97]
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When applications share access to a set of files, they need to be
implemented so as to take account of the possibility of conflicting
access by another application. This is true whether the applications
in question execute on different clients or reside on the same
client.
Share reservations and record locks are the facilities the NFS
version 4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFS version 4
protocol's data caching must be implemented such that it does not
invalidate the assumptions that those using these facilities depend
upon.
In order to avoid invalidating the sharing assumptions that
applications rely on, NFS version 4 clients should not provide cached
data to applications or modify it on behalf of an application when it
would not be valid to obtain or modify that same data via a READ or
WRITE operation.
Furthermore, in the absence of open delegation (see the section "Open
Delegation") two additional rules apply. Note that these rules are
obeyed in practice by many NFS version 2 and version 3 clients.
o First, cached data present on a client must be revalidated after
doing an OPEN. Revalidating means that the client fetches the
change attribute from the server, compares it with the cached
change attribute, and if different, declares the cached data (as
well as the cached attributes) as invalid. This is to ensure that
the data for the OPENed file is still correctly reflected in the
client's cache. This validation must be done at least when the
client's OPEN operation includes DENY=WRITE or BOTH thus
terminating a period in which other clients may have had the
opportunity to open the file with WRITE access. Clients may
choose to do the revalidation more often (i.e., at OPENs
specifying DENY=NONE) to parallel the NFS version 3 protocol's
practice for the benefit of users assuming this degree of cache
revalidation.
Since the change attribute is updated for data and metadata
modifications, some client implementors may be tempted to use the
time_modify attribute and not change to validate cached data, so
that metadata changes do not spuriously invalidate clean data.
The implementor is cautioned in this approach. The change
attribute is guaranteed to change for each update to the file,
Shepler, et al. Standards Track [Page 98]
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whereas time_modify is guaranteed to change only at the
granularity of the time_delta attribute. Use by the client's data
cache validation logic of time_modify and not change runs the risk
of the client incorrectly marking stale data as valid.
o Second, modified data must be flushed to the server before closing
a file OPENed for write. This is complementary to the first rule.
If the data is not flushed at CLOSE, the revalidation done after
client OPENs as file is unable to achieve its purpose. The other
aspect to flushing the data before close is that the data must be
committed to stable storage, at the server, before the CLOSE
operation is requested by the client. In the case of a server
reboot or restart and a CLOSEd file, it may not be possible to
retransmit the data to be written to the file. Hence, this
requirement.
For those applications that choose to use file locking instead of
share reservations to exclude inconsistent file access, there is an
analogous set of constraints that apply to client side data caching.
These rules are effective only if the file locking is used in a way
that matches in an equivalent way the actual READ and WRITE
operations executed. This is as opposed to file locking that is
based on pure convention. For example, it is possible to manipulate
a two-megabyte file by dividing the file into two one-megabyte
regions and protecting access to the two regions by file locks on
bytes zero and one. A lock for write on byte zero of the file would
represent the right to do READ and WRITE operations on the first
region. A lock for write on byte one of the file would represent the
right to do READ and WRITE operations on the second region. As long
as all applications manipulating the file obey this convention, they
will work on a local filesystem. However, they may not work with the
NFS version 4 protocol unless clients refrain from data caching.
The rules for data caching in the file locking environment are:
o First, when a client obtains a file lock for a particular region,
the data cache corresponding to that region (if any cached data
exists) must be revalidated. If the change attribute indicates
that the file may have been updated since the cached data was
obtained, the client must flush or invalidate the cached data for
the newly locked region. A client might choose to invalidate all
of non-modified cached data that it has for the file but the only
requirement for correct operation is to invalidate all of the data
in the newly locked region.
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o Second, before releasing a write lock for a region, all modified
data for that region must be flushed to the server. The modified
data must also be written to stable storage.
Note that flushing data to the server and the invalidation of cached
data must reflect the actual byte ranges locked or unlocked.
Rounding these up or down to reflect client cache block boundaries
will cause problems if not carefully done. For example, writing a
modified block when only half of that block is within an area being
unlocked may cause invalid modification to the region outside the
unlocked area. This, in turn, may be part of a region locked by
another client. Clients can avoid this situation by synchronously
performing portions of write operations that overlap that portion
(initial or final) that is not a full block. Similarly, invalidating
a locked area which is not an integral number of full buffer blocks
would require the client to read one or two partial blocks from the
server if the revalidation procedure shows that the data which the
client possesses may not be valid.
The data that is written to the server as a prerequisite to the
unlocking of a region must be written, at the server, to stable
storage. The client may accomplish this either with synchronous
writes or by following asynchronous writes with a COMMIT operation.
This is required because retransmission of the modified data after a
server reboot might conflict with a lock held by another client.
A client implementation may choose to accommodate applications which
use record locking in non-standard ways (e.g., using a record lock as
a global semaphore) by flushing to the server more data upon an LOCKU
than is covered by the locked range. This may include modified data
within files other than the one for which the unlocks are being done.
In such cases, the client must not interfere with applications whose
READs and WRITEs are being done only within the bounds of record
locks which the application holds. For example, an application locks
a single byte of a file and proceeds to write that single byte. A
client that chose to handle a LOCKU by flushing all modified data to
the server could validly write that single byte in response to an
unrelated unlock. However, it would not be valid to write the entire
block in which that single written byte was located since it includes
an area that is not locked and might be locked by another client.
Client implementations can avoid this problem by dividing files with
modified data into those for which all modifications are done to
areas covered by an appropriate record lock and those for which there
are modifications not covered by a record lock. Any writes done for
the former class of files must not include areas not locked and thus
not modified on the client.
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Client side data caching needs to respect mandatory file locking when
it is in effect. The presence of mandatory file locking for a given
file is indicated when the client gets back NFS4ERR_LOCKED from a
READ or WRITE on a file it has an appropriate share reservation for.
When mandatory locking is in effect for a file, the client must check
for an appropriate file lock for data being read or written. If a
lock exists for the range being read or written, the client may
satisfy the request using the client's validated cache. If an
appropriate file lock is not held for the range of the read or write,
the read or write request must not be satisfied by the client's cache
and the request must be sent to the server for processing. When a
read or write request partially overlaps a locked region, the request
should be subdivided into multiple pieces with each region (locked or
not) treated appropriately.
When clients cache data, the file data needs to be organized
according to the filesystem object to which the data belongs. For
NFS version 3 clients, the typical practice has been to assume for
the purpose of caching that distinct filehandles represent distinct
filesystem objects. The client then has the choice to organize and
maintain the data cache on this basis.
In the NFS version 4 protocol, there is now the possibility to have
significant deviations from a "one filehandle per object" model
because a filehandle may be constructed on the basis of the object's
pathname. Therefore, clients need a reliable method to determine if
two filehandles designate the same filesystem object. If clients
were simply to assume that all distinct filehandles denote distinct
objects and proceed to do data caching on this basis, caching
inconsistencies would arise between the distinct client side objects
which mapped to the same server side object.
By providing a method to differentiate filehandles, the NFS version 4
protocol alleviates a potential functional regression in comparison
with the NFS version 3 protocol. Without this method, caching
inconsistencies within the same client could occur and this has not
been present in previous versions of the NFS protocol. Note that it
is possible to have such inconsistencies with applications executing
on multiple clients but that is not the issue being addressed here.
For the purposes of data caching, the following steps allow an NFS
version 4 client to determine whether two distinct filehandles denote
the same server side object:
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o If GETATTR directed to two filehandles returns different values of
the fsid attribute, then the filehandles represent distinct
objects.
o If GETATTR for any file with an fsid that matches the fsid of the
two filehandles in question returns a unique_handles attribute
with a value of TRUE, then the two objects are distinct.
o If GETATTR directed to the two filehandles does not return the
fileid attribute for both of the handles, then it cannot be
determined whether the two objects are the same. Therefore,
operations which depend on that knowledge (e.g., client side data
caching) cannot be done reliably.
o If GETATTR directed to the two filehandles returns different
values for the fileid attribute, then they are distinct objects.
o Otherwise they are the same object.
When a file is being OPENed, the server may delegate further handling
of opens and closes for that file to the opening client. Any such
delegation is recallable, since the circumstances that allowed for
the delegation are subject to change. In particular, the server may
receive a conflicting OPEN from another client, the server must
recall the delegation before deciding whether the OPEN from the other
client may be granted. Making a delegation is up to the server and
clients should not assume that any particular OPEN either will or
will not result in an open delegation. The following is a typical
set of conditions that servers might use in deciding whether OPEN
should be delegated:
o The client must be able to respond to the server's callback
requests. The server will use the CB_NULL procedure for a test of
callback ability.
o The client must have responded properly to previous recalls.
o There must be no current open conflicting with the requested
delegation.
o There should be no current delegation that conflicts with the
delegation being requested.
o The probability of future conflicting open requests should be low
based on the recent history of the file.
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o The existence of any server-specific semantics of OPEN/CLOSE that
would make the required handling incompatible with the prescribed
handling that the delegated client would apply (see below).
There are two types of open delegations, read and write. A read open
delegation allows a client to handle, on its own, requests to open a
file for reading that do not deny read access to others. Multiple
read open delegations may be outstanding simultaneously and do not
conflict. A write open delegation allows the client to handle, on
its own, all opens. Only one write open delegation may exist for a
given file at a given time and it is inconsistent with any read open
delegations.
When a client has a read open delegation, it may not make any changes
to the contents or attributes of the file but it is assured that no
other client may do so. When a client has a write open delegation,
it may modify the file data since no other client will be accessing
the file's data. The client holding a write delegation may only
affect file attributes which are intimately connected with the file
data: size, time_modify, change.
When a client has an open delegation, it does not send OPENs or
CLOSEs to the server but updates the appropriate status internally.
For a read open delegation, opens that cannot be handled locally
(opens for write or that deny read access) must be sent to the
server.
When an open delegation is made, the response to the OPEN contains an
open delegation structure which specifies the following:
o the type of delegation (read or write)
o space limitation information to control flushing of data on close
(write open delegation only, see the section "Open Delegation and
Data Caching")
o an nfsace4 specifying read and write permissions
o a stateid to represent the delegation for READ and WRITE
The delegation stateid is separate and distinct from the stateid for
the OPEN proper. The standard stateid, unlike the delegation
stateid, is associated with a particular lock_owner and will continue
to be valid after the delegation is recalled and the file remains
open.
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When a request internal to the client is made to open a file and open
delegation is in effect, it will be accepted or rejected solely on
the basis of the following conditions. Any requirement for other
checks to be made by the delegate should result in open delegation
being denied so that the checks can be made by the server itself.
o The access and deny bits for the request and the file as described
in the section "Share Reservations".
o The read and write permissions as determined below.
The nfsace4 passed with delegation can be used to avoid frequent
ACCESS calls. The permission check should be as follows:
o If the nfsace4 indicates that the open may be done, then it should
be granted without reference to the server.
o If the nfsace4 indicates that the open may not be done, then an
ACCESS request must be sent to the server to obtain the definitive
answer.
The server may return an nfsace4 that is more restrictive than the
actual ACL of the file. This includes an nfsace4 that specifies
denial of all access. Note that some common practices such as
mapping the traditional user "root" to the user "nobody" may make it
incorrect to return the actual ACL of the file in the delegation
response.
The use of delegation together with various other forms of caching
creates the possibility that no server authentication will ever be
performed for a given user since all of the user's requests might be
satisfied locally. Where the client is depending on the server for
authentication, the client should be sure authentication occurs for
each user by use of the ACCESS operation. This should be the case
even if an ACCESS operation would not be required otherwise. As
mentioned before, the server may enforce frequent authentication by
returning an nfsace4 denying all access with every open delegation.
OPEN delegation allows much of the message overhead associated with
the opening and closing files to be eliminated. An open when an open
delegation is in effect does not require that a validation message be
sent to the server. The continued endurance of the "read open
delegation" provides a guarantee that no OPEN for write and thus no
write has occurred. Similarly, when closing a file opened for write
and if write open delegation is in effect, the data written does not
have to be flushed to the server until the open delegation is
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RFC 3530 NFS version 4 Protocol April 2003
recalled. The continued endurance of the open delegation provides a
guarantee that no open and thus no read or write has been done by
another client.
For the purposes of open delegation, READs and WRITEs done without an
OPEN are treated as the functional equivalents of a corresponding
type of OPEN. This refers to the READs and WRITEs that use the
special stateids consisting of all zero bits or all one bits.
Therefore, READs or WRITEs with a special stateid done by another
client will force the server to recall a write open delegation. A
WRITE with a special stateid done by another client will force a
recall of read open delegations.
With delegations, a client is able to avoid writing data to the
server when the CLOSE of a file is serviced. The file close system
call is the usual point at which the client is notified of a lack of
stable storage for the modified file data generated by the
application. At the close, file data is written to the server and
through normal accounting the server is able to determine if the
available filesystem space for the data has been exceeded (i.e.,
server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT). This accounting
includes quotas. The introduction of delegations requires that a
alternative method be in place for the same type of communication to
occur between client and server.
In the delegation response, the server provides either the limit of
the size of the file or the number of modified blocks and associated
block size. The server must ensure that the client will be able to
flush data to the server of a size equal to that provided in the
original delegation. The server must make this assurance for all
outstanding delegations. Therefore, the server must be careful in
its management of available space for new or modified data taking
into account available filesystem space and any applicable quotas.
The server can recall delegations as a result of managing the
available filesystem space. The client should abide by the server's
state space limits for delegations. If the client exceeds the stated
limits for the delegation, the server's behavior is undefined.
Based on server conditions, quotas or available filesystem space, the
server may grant write open delegations with very restrictive space
limitations. The limitations may be defined in a way that will
always force modified data to be flushed to the server on close.
With respect to authentication, flushing modified data to the server
after a CLOSE has occurred may be problematic. For example, the user
of the application may have logged off the client and unexpired
authentication credentials may not be present. In this case, the
client may need to take special care to ensure that local unexpired
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RFC 3530 NFS version 4 Protocol April 2003
credentials will in fact be available. This may be accomplished by
tracking the expiration time of credentials and flushing data well in
advance of their expiration or by making private copies of
credentials to assure their availability when needed.
When a client holds a write open delegation, lock operations may be
performed locally. This includes those required for mandatory file
locking. This can be done since the delegation implies that there
can be no conflicting locks. Similarly, all of the revalidations
that would normally be associated with obtaining locks and the
flushing of data associated with the releasing of locks need not be
done.
When a client holds a read open delegation, lock operations are not
performed locally. All lock operations, including those requesting
non-exclusive locks, are sent to the server for resolution.
The server needs to employ special handling for a GETATTR where the
target is a file that has a write open delegation in effect. The
reason for this is that the client holding the write delegation may
have modified the data and the server needs to reflect this change to
the second client that submitted the GETATTR. Therefore, the client
holding the write delegation needs to be interrogated. The server
will use the CB_GETATTR operation. The only attributes that the
server can reliably query via CB_GETATTR are size and change.
Since CB_GETATTR is being used to satisfy another client's GETATTR
request, the server only needs to know if the client holding the
delegation has a modified version of the file. If the client's copy
of the delegated file is not modified (data or size), the server can
satisfy the second client's GETATTR request from the attributes
stored locally at the server. If the file is modified, the server
only needs to know about this modified state. If the server
determines that the file is currently modified, it will respond to
the second client's GETATTR as if the file had been modified locally
at the server.
Since the form of the change attribute is determined by the server
and is opaque to the client, the client and server need to agree on a
method of communicating the modified state of the file. For the size
attribute, the client will report its current view of the file size.
For the change attribute, the handling is more involved.
Shepler, et al. Standards Track [Page 106]
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For the client, the following steps will be taken when receiving a
write delegation:
o The value of the change attribute will be obtained from the server
and cached. Let this value be represented by c.
o The client will create a value greater than c that will be used
for communicating modified data is held at the client. Let this
value be represented by d.
o When the client is queried via CB_GETATTR for the change
attribute, it checks to see if it holds modified data. If the
file is modified, the value d is returned for the change attribute
value. If this file is not currently modified, the client returns
the value c for the change attribute.
For simplicity of implementation, the client MAY for each CB_GETATTR
return the same value d. This is true even if, between successive
CB_GETATTR operations, the client again modifies in the file's data
or metadata in its cache. The client can return the same value
because the only requirement is that the client be able to indicate
to the server that the client holds modified data. Therefore, the
value of d may always be c + 1.
While the change attribute is opaque to the client in the sense that
it has no idea what units of time, if any, the server is counting
change with, it is not opaque in that the client has to treat it as
an unsigned integer, and the server has to be able to see the results
of the client's changes to that integer. Therefore, the server MUST
encode the change attribute in network order when sending it to the
client. The client MUST decode it from network order to its native
order when receiving it and the client MUST encode it network order
when sending it to the server. For this reason, change is defined as
an unsigned integer rather than an opaque array of octets.
For the server, the following steps will be taken when providing a
write delegation:
o Upon providing a write delegation, the server will cache a copy of
the change attribute in the data structure it uses to record the
delegation. Let this value be represented by sc.
o When a second client sends a GETATTR operation on the same file to
the server, the server obtains the change attribute from the first
client. Let this value be cc.
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o If the value cc is equal to sc, the file is not modified and the
server returns the current values for change, time_metadata, and
time_modify (for example) to the second client.
o If the value cc is NOT equal to sc, the file is currently modified
at the first client and most likely will be modified at the server
at a future time. The server then uses its current time to
construct attribute values for time_metadata and time_modify. A
new value of sc, which we will call nsc, is computed by the
server, such that nsc >= sc + 1. The server then returns the
constructed time_metadata, time_modify, and nsc values to the
requester. The server replaces sc in the delegation record with
nsc. To prevent the possibility of time_modify, time_metadata,
and change from appearing to go backward (which would happen if
the client holding the delegation fails to write its modified data
to the server before the delegation is revoked or returned), the
server SHOULD update the file's metadata record with the
constructed attribute values. For reasons of reasonable
performance, committing the constructed attribute values to stable
storage is OPTIONAL.
As discussed earlier in this section, the client MAY return the
same cc value on subsequent CB_GETATTR calls, even if the file was
modified in the client's cache yet again between successive
CB_GETATTR calls. Therefore, the server must assume that the file
has been modified yet again, and MUST take care to ensure that the
new nsc it constructs and returns is greater than the previous nsc
it returned. An example implementation's delegation record would
satisfy this mandate by including a boolean field (let us call it
"modified") that is set to false when the delegation is granted,
and an sc value set at the time of grant to the change attribute
value. The modified field would be set to true the first time cc
!= sc, and would stay true until the delegation is returned or
revoked. The processing for constructing nsc, time_modify, and
time_metadata would use this pseudo code:
if (!modified) {
do CB_GETATTR for change and size;
if (cc != sc)
modified = TRUE;
} else {
do CB_GETATTR for size;
}
if (modified) {
sc = sc + 1;
time_modify = time_metadata = current_time;
Shepler, et al. Standards Track [Page 108]
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update sc, time_modify, time_metadata into file's metadata;
}
return to client (that sent GETATTR) the attributes
it requested, but make sure size comes from what
CB_GETATTR returned. Do not update the file's metadata
with the client's modified size.
o In the case that the file attribute size is different than the
server's current value, the server treats this as a modification
regardless of the value of the change attribute retrieved via
CB_GETATTR and responds to the second client as in the last step.
This methodology resolves issues of clock differences between client
and server and other scenarios where the use of CB_GETATTR break
down.
It should be noted that the server is under no obligation to use
CB_GETATTR and therefore the server MAY simply recall the delegation
to avoid its use.
The following events necessitate recall of an open delegation:
o Potentially conflicting OPEN request (or READ/WRITE done with
"special" stateid)
o SETATTR issued by another client
o REMOVE request for the file
o RENAME request for the file as either source or target of the
RENAME
Whether a RENAME of a directory in the path leading to the file
results in recall of an open delegation depends on the semantics of
the server filesystem. If that filesystem denies such RENAMEs when a
file is open, the recall must be performed to determine whether the
file in question is, in fact, open.
In addition to the situations above, the server may choose to recall
open delegations at any time if resource constraints make it
advisable to do so. Clients should always be prepared for the
possibility of recall.
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When a client receives a recall for an open delegation, it needs to
update state on the server before returning the delegation. These
same updates must be done whenever a client chooses to return a
delegation voluntarily. The following items of state need to be
dealt with:
o If the file associated with the delegation is no longer open and
no previous CLOSE operation has been sent to the server, a CLOSE
operation must be sent to the server.
o If a file has other open references at the client, then OPEN
operations must be sent to the server. The appropriate stateids
will be provided by the server for subsequent use by the client
since the delegation stateid will not longer be valid. These OPEN
requests are done with the claim type of CLAIM_DELEGATE_CUR. This
will allow the presentation of the delegation stateid so that the
client can establish the appropriate rights to perform the OPEN.
(see the section "Operation 18: OPEN" for details.)
o If there are granted file locks, the corresponding LOCK operations
need to be performed. This applies to the write open delegation
case only.
o For a write open delegation, if at the time of recall the file is
not open for write, all modified data for the file must be flushed
to the server. If the delegation had not existed, the client
would have done this data flush before the CLOSE operation.
o For a write open delegation when a file is still open at the time
of recall, any modified data for the file needs to be flushed to
the server.
o With the write open delegation in place, it is possible that the
file was truncated during the duration of the delegation. For
example, the truncation could have occurred as a result of an OPEN
UNCHECKED with a size attribute value of zero. Therefore, if a
truncation of the file has occurred and this operation has not
been propagated to the server, the truncation must occur before
any modified data is written to the server.
In the case of write open delegation, file locking imposes some
additional requirements. To precisely maintain the associated
invariant, it is required to flush any modified data in any region
for which a write lock was released while the write delegation was in
effect. However, because the write open delegation implies no other
locking by other clients, a simpler implementation is to flush all
modified data for the file (as described just above) if any write
lock has been released while the write open delegation was in effect.
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An implementation need not wait until delegation recall (or deciding
to voluntarily return a delegation) to perform any of the above
actions, if implementation considerations (e.g., resource
availability constraints) make that desirable. Generally, however,
the fact that the actual open state of the file may continue to
change makes it not worthwhile to send information about opens and
closes to the server, except as part of delegation return. Only in
the case of closing the open that resulted in obtaining the
delegation would clients be likely to do this early, since, in that
case, the close once done will not be undone. Regardless of the
client's choices on scheduling these actions, all must be performed
before the delegation is returned, including (when applicable) the
close that corresponds to the open that resulted in the delegation.
These actions can be performed either in previous requests or in
previous operations in the same COMPOUND request.
A client may fail to respond to a recall for various reasons, such as
a failure of the callback path from server to the client. The client
may be unaware of a failure in the callback path. This lack of
awareness could result in the client finding out long after the
failure that its delegation has been revoked, and another client has
modified the data for which the client had a delegation. This is
especially a problem for the client that held a write delegation.
The server also has a dilemma in that the client that fails to
respond to the recall might also be sending other NFS requests,
including those that renew the lease before the lease expires.
Without returning an error for those lease renewing operations, the
server leads the client to believe that the delegation it has is in
force.
This difficulty is solved by the following rules:
o When the callback path is down, the server MUST NOT revoke the
delegation if one of the following occurs:
- The client has issued a RENEW operation and the server has
returned an NFS4ERR_CB_PATH_DOWN error. The server MUST renew
the lease for any record locks and share reservations the
client has that the server has known about (as opposed to those
locks and share reservations the client has established but not
yet sent to the server, due to the delegation). The server
SHOULD give the client a reasonable time to return its
delegations to the server before revoking the client's
delegations.
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- The client has not issued a RENEW operation for some period of
time after the server attempted to recall the delegation. This
period of time MUST NOT be less than the value of the
lease_time attribute.
o When the client holds a delegation, it can not rely on operations,
except for RENEW, that take a stateid, to renew delegation leases
across callback path failures. The client that wants to keep
delegations in force across callback path failures must use RENEW
to do so.
At the point a delegation is revoked, if there are associated opens
on the client, the applications holding these opens need to be
notified. This notification usually occurs by returning errors for
READ/WRITE operations or when a close is attempted for the open file.
If no opens exist for the file at the point the delegation is
revoked, then notification of the revocation is unnecessary.
However, if there is modified data present at the client for the
file, the user of the application should be notified. Unfortunately,
it may not be possible to notify the user since active applications
may not be present at the client. See the section "Revocation
Recovery for Write Open Delegation" for additional details.
When locks and delegations are revoked, the assumptions upon which
successful caching depend are no longer guaranteed. For any locks or
share reservations that have been revoked, the corresponding owner
needs to be notified. This notification includes applications with a
file open that has a corresponding delegation which has been revoked.
Cached data associated with the revocation must be removed from the
client. In the case of modified data existing in the client's cache,
that data must be removed from the client without it being written to
the server. As mentioned, the assumptions made by the client are no
longer valid at the point when a lock or delegation has been revoked.
For example, another client may have been granted a conflicting lock
after the revocation of the lock at the first client. Therefore, the
data within the lock range may have been modified by the other
client. Obviously, the first client is unable to guarantee to the
application what has occurred to the file in the case of revocation.
Notification to a lock owner will in many cases consist of simply
returning an error on the next and all subsequent READs/WRITEs to the
open file or on the close. Where the methods available to a client
make such notification impossible because errors for certain
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operations may not be returned, more drastic action such as signals
or process termination may be appropriate. The justification for
this is that an invariant for which an application depends on may be
violated. Depending on how errors are typically treated for the
client operating environment, further levels of notification
including logging, console messages, and GUI pop-ups may be
appropriate.
Revocation recovery for a write open delegation poses the special
issue of modified data in the client cache while the file is not
open. In this situation, any client which does not flush modified
data to the server on each close must ensure that the user receives
appropriate notification of the failure as a result of the
revocation. Since such situations may require human action to
correct problems, notification schemes in which the appropriate user
or administrator is notified may be necessary. Logging and console
messages are typical examples.
If there is modified data on the client, it must not be flushed
normally to the server. A client may attempt to provide a copy of
the file data as modified during the delegation under a different
name in the filesystem name space to ease recovery. Note that when
the client can determine that the file has not been modified by any
other client, or when the client has a complete cached copy of file
in question, such a saved copy of the client's view of the file may
be of particular value for recovery. In other case, recovery using a
copy of the file based partially on the client's cached data and
partially on the server copy as modified by other clients, will be
anything but straightforward, so clients may avoid saving file
contents in these situations or mark the results specially to warn
users of possible problems.
Saving of such modified data in delegation revocation situations may
be limited to files of a certain size or might be used only when
sufficient disk space is available within the target filesystem.
Such saving may also be restricted to situations when the client has
sufficient buffering resources to keep the cached copy available
until it is properly stored to the target filesystem.
The attributes discussed in this section do not include named
attributes. Individual named attributes are analogous to files and
caching of the data for these needs to be handled just as data
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caching is for ordinary files. Similarly, LOOKUP results from an
OPENATTR directory are to be cached on the same basis as any other
pathnames and similarly for directory contents.
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. Such caching is write
through in that modification to file attributes is always done by
means of requests to the server and should not be done locally and
cached. The exception to this are modifications to attributes that
are intimately connected with data caching. Therefore, extending a
file by writing data to the local data cache is reflected immediately
in the size as seen on the client without this change being
immediately reflected on the server. Normally such changes are not
propagated directly to the server but when the modified data is
flushed to the server, analogous attribute changes are made on the
server. When open delegation is in effect, the modified attributes
may be returned to the server in the response to a CB_RECALL call.
The result of local caching of attributes is that the attribute
caches maintained on individual clients will not be coherent.
Changes made in one order on the server may be seen in a different
order on one client and in a third order on a different client.
The typical filesystem application programming interfaces do not
provide means to atomically modify or interrogate attributes for
multiple files at the same time. The following rules provide an
environment where the potential incoherences mentioned above can be
reasonably managed. These rules are derived from the practice of
previous NFS protocols.
o All attributes for a given file (per-fsid attributes excepted) are
cached as a unit at the client so that no non-serializability can
arise within the context of a single file.
o An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server.
o When operations are performed that change attributes at the
server, the updated attribute set is requested as part of the
containing RPC. This includes directory operations that update
attributes indirectly. This is accomplished by following the
modifying operation with a GETATTR operation and then using the
results of the GETATTR to update the client's cached attributes.
Note that if the full set of attributes to be cached is requested by
READDIR, the results can be cached by the client on the same basis as
attributes obtained via GETATTR.
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A client may validate its cached version of attributes for a file by
fetching just both the change and time_access attributes and assuming
that if the change attribute has the same value as it did when the
attributes were cached, then no attributes other than time_access
have changed. The reason why time_access is also fetched is because
many servers operate in environments where the operation that updates
change does not update time_access. For example, POSIX file
semantics do not update access time when a file is modified by the
write system call. Therefore, the client that wants a current
time_access value should fetch it with change during the attribute
cache validation processing and update its cached time_access.
The client may maintain a cache of modified attributes for those
attributes intimately connected with data of modified regular files
(size, time_modify, and change). Other than those three attributes,
the client MUST NOT maintain a cache of modified attributes.
Instead, attribute changes are immediately sent to the server.
In some operating environments, the equivalent to time_access is
expected to be implicitly updated by each read of the content of the
file object. If an NFS client is caching the content of a file
object, whether it is a regular file, directory, or symbolic link,
the client SHOULD NOT update the time_access attribute (via SETATTR
or a small READ or READDIR request) on the server with each read that
is satisfied from cache. The reason is that this can defeat the
performance benefits of caching content, especially since an explicit
SETATTR of time_access may alter the change attribute on the server.
If the change attribute changes, clients that are caching the content
will think the content has changed, and will re-read unmodified data
from the server. Nor is the client encouraged to maintain a modified
version of time_access in its cache, since this would mean that the
client will either eventually have to write the access time to the
server with bad performance effects, or it would never update the
server's time_access, thereby resulting in a situation where an
application that caches access time between a close and open of the
same file observes the access time oscillating between the past and
present. The time_access attribute always means the time of last
access to a file by a read that was satisfied by the server. This
way clients will tend to see only time_access changes that go forward
in time.
Some operating environments include the capability for an application
to map a file's content into the application's address space. Each
time the application accesses a memory location that corresponds to a
block that has not been loaded into the address space, a page fault
occurs and the file is read (or if the block does not exist in the
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file, the block is allocated and then instantiated in the
application's address space).
As long as each memory mapped access to the file requires a page
fault, the relevant attributes of the file that are used to detect
access and modification (time_access, time_metadata, time_modify, and
change) will be updated. However, in many operating environments,
when page faults are not required these attributes will not be
updated on reads or updates to the file via memory access (regardless
whether the file is local file or is being access remotely). A
client or server MAY fail to update attributes of a file that is
being accessed via memory mapped I/O. This has several implications:
o If there is an application on the server that has memory mapped a
file that a client is also accessing, the client may not be able
to get a consistent value of the change attribute to determine
whether its cache is stale or not. A server that knows that the
file is memory mapped could always pessimistically return updated
values for change so as to force the application to always get the
most up to date data and metadata for the file. However, due to
the negative performance implications of this, such behavior is
OPTIONAL.
o If the memory mapped file is not being modified on the server, and
instead is just being read by an application via the memory mapped
interface, the client will not see an updated time_access
attribute. However, in many operating environments, neither will
any process running on the server. Thus NFS clients are at no
disadvantage with respect to local processes.
o If there is another client that is memory mapping the file, and if
that client is holding a write delegation, the same set of issues
as discussed in the previous two bullet items apply. So, when a
server does a CB_GETATTR to a file that the client has modified in
its cache, the response from CB_GETATTR will not necessarily be
accurate. As discussed earlier, the client's obligation is to
report that the file has been modified since the delegation was
granted, not whether it has been modified again between successive
CB_GETATTR calls, and the server MUST assume that any file the
client has modified in cache has been modified again between
successive CB_GETATTR calls. Depending on the nature of the
client's memory management system, this weak obligation may not be
possible. A client MAY return stale information in CB_GETATTR
whenever the file is memory mapped.
o The mixture of memory mapping and file locking on the same file is
problematic. Consider the following scenario, where the page size
on each client is 8192 bytes.
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- Client A memory maps first page (8192 bytes) of file X
- Client B memory maps first page (8192 bytes) of file X
- Client A write locks first 4096 bytes
- Client B write locks second 4096 bytes
- Client A, via a STORE instruction modifies part of its locked
region.
- Simultaneous to client A, client B issues a STORE on part of
its locked region.
Here the challenge is for each client to resynchronize to get a
correct view of the first page. In many operating environments, the
virtual memory management systems on each client only know a page is
modified, not that a subset of the page corresponding to the
respective lock regions has been modified. So it is not possible for
each client to do the right thing, which is to only write to the
server that portion of the page that is locked. For example, if
client A simply writes out the page, and then client B writes out the
page, client A's data is lost.
Moreover, if mandatory locking is enabled on the file, then we have a
different problem. When clients A and B issue the STORE
instructions, the resulting page faults require a record lock on the
entire page. Each client then tries to extend their locked range to
the entire page, which results in a deadlock.
Communicating the NFS4ERR_DEADLOCK error to a STORE instruction is
difficult at best.
If a client is locking the entire memory mapped file, there is no
problem with advisory or mandatory record locking, at least until the
client unlocks a region in the middle of the file.
Given the above issues the following are permitted:
- Clients and servers MAY deny memory mapping a file they know there
are record locks for.
- Clients and servers MAY deny a record lock on a file they know is
memory mapped.
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- A client MAY deny memory mapping a file that it knows requires
mandatory locking for I/O. If mandatory locking is enabled after
the file is opened and mapped, the client MAY deny the application
further access to its mapped file.
The results of LOOKUP and READDIR operations may be cached to avoid
the cost of subsequent LOOKUP operations. Just as in the case of
attribute caching, inconsistencies may arise among the various client
caches. To mitigate the effects of these inconsistencies and given
the context of typical filesystem APIs, an upper time boundary is
maintained on how long a client name cache entry can be kept without
verifying that the entry has not been made invalid by a directory
change operation performed by another client.
When a client is not making changes to a directory for which there
exist name cache entries, the client needs to periodically fetch
attributes for that directory to ensure that it is not being
modified. After determining that no modification has occurred, the
expiration time for the associated name cache entries may be updated
to be the current time plus the name cache staleness bound.
When a client is making changes to a given directory, it needs to
determine whether there have been changes made to the directory by
other clients. It does this by using the change attribute as
reported before and after the directory operation in the associated
change_info4 value returned for the operation. The server is able to
communicate to the client whether the change_info4 data is provided
atomically with respect to the directory operation. If the change
values are provided atomically, the client is then able to compare
the pre-operation change value with the change value in the client's
name cache. If the comparison indicates that the directory was
updated by another client, the name cache associated with the
modified directory is purged from the client. If the comparison
indicates no modification, the name cache can be updated on the
client to reflect the directory operation and the associated timeout
extended. The post-operation change value needs to be saved as the
basis for future change_info4 comparisons.
As demonstrated by the scenario above, name caching requires that the
client revalidate name cache data by inspecting the change attribute
of a directory at the point when the name cache item was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre and post
operation change attribute values atomically. When the server is
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unable to report the before and after values atomically with respect
to the directory operation, the server must indicate that fact in the
change_info4 return value. When the information is not atomically
reported, the client should not assume that other clients have not
changed the directory.
The results of READDIR operations may be used to avoid subsequent
READDIR operations. Just as in the cases of attribute and name
caching, inconsistencies may arise among the various client caches.
To mitigate the effects of these inconsistencies, and given the
context of typical filesystem APIs, the following rules should be
followed:
o Cached READDIR information for a directory which is not obtained
in a single READDIR operation must always be a consistent snapshot
of directory contents. This is determined by using a GETATTR
before the first READDIR and after the last of READDIR that
contributes to the cache.
o An upper time boundary is maintained to indicate the length of
time a directory cache entry is considered valid before the client
must revalidate the cached information.
The revalidation technique parallels that discussed in the case of
name caching. When the client is not changing the directory in
question, checking the change attribute of the directory with GETATTR
is adequate. The lifetime of the cache entry can be extended at
these checkpoints. When a client is modifying the directory, the
client needs to use the change_info4 data to determine whether there
are other clients modifying the directory. If it is determined that
no other client modifications are occurring, the client may update
its directory cache to reflect its own changes.
As demonstrated previously, directory caching requires that the
client revalidate directory cache data by inspecting the change
attribute of a directory at the point when the directory was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre and post
operation change attribute values atomically. When the server is
unable to report the before and after values atomically with respect
to the directory operation, the server must indicate that fact in the
change_info4 return value. When the information is not atomically
reported, the client should not assume that other clients have not
changed the directory.
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To address the requirement of an NFS protocol that can evolve as the
need arises, the NFS version 4 protocol contains the rules and
framework to allow for future minor changes or versioning.
The base assumption with respect to minor versioning is that any
future accepted minor version must follow the IETF process and be
documented in a standards track RFC. Therefore, each minor version
number will correspond to an RFC. Minor version zero of the NFS
version 4 protocol is represented by this RFC. The COMPOUND
procedure will support the encoding of the minor version being
requested by the client.
The following items represent the basic rules for the development of
minor versions. Note that a future minor version may decide to
modify or add to the following rules as part of the minor version
definition.
1. Procedures are not added or deleted
To maintain the general RPC model, NFS version 4 minor versions
will not add to or delete procedures from the NFS program.
2. Minor versions may add operations to the COMPOUND and
CB_COMPOUND procedures.
The addition of operations to the COMPOUND and CB_COMPOUND
procedures does not affect the RPC model.
2.1 Minor versions may append attributes to GETATTR4args, bitmap4,
and GETATTR4res.
This allows for the expansion of the attribute model to allow
for future growth or adaptation.
2.2 Minor version X must append any new attributes after the last
documented attribute.
Since attribute results are specified as an opaque array of
per-attribute XDR encoded results, the complexity of adding new
attributes in the midst of the current definitions will be too
burdensome.
3. Minor versions must not modify the structure of an existing
operation's arguments or results.
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Again the complexity of handling multiple structure definitions
for a single operation is too burdensome. New operations should
be added instead of modifying existing structures for a minor
version.
This rule does not preclude the following adaptations in a minor
version.
o adding bits to flag fields such as new attributes to GETATTR's
bitmap4 data type
o adding bits to existing attributes like ACLs that have flag
words
o extending enumerated types (including NFS4ERR_*) with new
values
4. Minor versions may not modify the structure of existing
attributes.
5. Minor versions may not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
6. Minor versions may not delete attributes.
7. Minor versions may not delete flag bits or enumeration values.
8. Minor versions may declare an operation as mandatory to NOT
implement.
Specifying an operation as "mandatory to not implement" is
equivalent to obsoleting an operation. For the client, it means
that the operation should not be sent to the server. For the
server, an NFS error can be returned as opposed to "dropping"
the request as an XDR decode error. This approach allows for
the obsolescence of an operation while maintaining its structure
so that a future minor version can reintroduce the operation.
8.1 Minor versions may declare attributes mandatory to NOT
implement.
8.2 Minor versions may declare flag bits or enumeration values as
mandatory to NOT implement.
9. Minor versions may downgrade features from mandatory to
recommended, or recommended to optional.
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10. Minor versions may upgrade features from optional to recommended
or recommended to mandatory.
11. A client and server that support minor version X must support
minor versions 0 (zero) through X-1 as well.
12. No new features may be introduced as mandatory in a minor
version.
This rule allows for the introduction of new functionality and
forces the use of implementation experience before designating a
feature as mandatory.
13. A client MUST NOT attempt to use a stateid, filehandle, or
similar returned object from the COMPOUND procedure with minor
version X for another COMPOUND procedure with minor version Y,
where X != Y.
The primary issue in which NFS version 4 needs to deal with
internationalization, or I18N, is with respect to file names and
other strings as used within the protocol. The choice of string
representation must allow reasonable name/string access to clients
which use various languages. The UTF-8 encoding of the UCS as
defined by [ISO10646] allows for this type of access and follows the
policy described in "IETF Policy on Character Sets and Languages",
[RFC2277].
[RFC3454], otherwise know as "stringprep", documents a framework for
using Unicode/UTF-8 in networking protocols, so as "to increase the
likelihood that string input and string comparison work in ways that
make sense for typical users throughout the world." A protocol must
define a profile of stringprep "in order to fully specify the
processing options." The remainder of this Internationalization
section defines the NFS version 4 stringprep profiles. Much of
terminology used for the remainder of this section comes from
stringprep.
There are three UTF-8 string types defined for NFS version 4:
utf8str_cs, utf8str_cis, and utf8str_mixed. Separate profiles are
defined for each. Each profile defines the following, as required by
stringprep:
o The intended applicability of the profile
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o The character repertoire that is the input and output to
stringprep (which is Unicode 3.2 for referenced version of
stringprep)
o The mapping tables from stringprep used (as described in section 3
of stringprep)
o Any additional mapping tables specific to the profile
o The Unicode normalization used, if any (as described in section 4
of stringprep)
o The tables from stringprep listing of characters that are
prohibited as output (as described in section 5 of stringprep)
o The bidirectional string testing used, if any (as described in
section 6 of stringprep)
o Any additional characters that are prohibited as output specific
to the profile
Stringprep discusses Unicode characters, whereas NFS version 4
renders UTF-8 characters. Since there is a one to one mapping from
UTF-8 to Unicode, where ever the remainder of this document refers to
to Unicode, the reader should assume UTF-8.
Much of the text for the profiles comes from [RFC3454].
The utf8str_cs type is a case sensitive string of UTF-8 characters.
Its primary use in NFS Version 4 is for naming components and
pathnames. Components and pathnames are stored on the server's
filesystem. Two valid distinct UTF-8 strings might be the same after
processing via the utf8str_cs profile. If the strings are two names
inside a directory, the NFS version 4 server will need to either:
o disallow the creation of a second name if it's post processed form
collides with that of an existing name, or
o allow the creation of the second name, but arrange so that after
post processing, the second name is different than the post
processed form of the first name.
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The nfs4_cs_prep profile specifies mapping using the following tables
from stringprep:
Table B.1
Table B.2 is normally not part of the nfs4_cs_prep profile as it is
primarily for dealing with case-insensitive comparisons. However, if
the NFS version 4 file server supports the case_insensitive
filesystem attribute, and if case_insensitive is true, the NFS
version 4 server MUST use Table B.2 (in addition to Table B1) when
processing utf8str_cs strings, and the NFS version 4 client MUST
assume Table B.2 (in addition to Table B.1) are being used.
If the case_preserving attribute is present and set to false, then
the NFS version 4 server MUST use table B.2 to map case when
processing utf8str_cs strings. Whether the server maps from lower to
upper case or the upper to lower case is an implementation
dependency.
The nfs4_cs_prep profile does not specify a normalization form. A
later revision of this specification may specify a particular
normalization form. Therefore, the server and client can expect that
they may receive unnormalized characters within protocol requests and
responses. If the operating environment requires normalization, then
the implementation must normalize utf8str_cs strings within the
protocol before presenting the information to an application (at the
client) or local filesystem (at the server).
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The nfs4_cs_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
The nfs4_cis_prep profile specifies using Unicode normalization form
KC, as described in stringprep.
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The utf8str_mixed type is a string of UTF-8 characters, with a prefix
that is case sensitive, a separator equal to '@', and a suffix that
is fully qualified domain name. Its primary use in NFS Version 4 is
for naming principals identified in an Access Control Entry.
For the prefix and the separator of a utf8str_mixed string, the
nfs4_mixed_prep profile specifies mapping using the following table
from stringprep:
Table B.1
For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
specifies mapping using the following tables from stringprep:
Shepler, et al. Standards Track [Page 126]
RFC 3530 NFS version 4 Protocol April 2003
Table B.1
Table B.2
Where the client sends an invalid UTF-8 string, the server should
return an NFS4ERR_INVAL error. This includes cases in which
inappropriate prefixes are detected and where the count includes
trailing bytes that do not constitute a full UCS character.
Where the client supplied string is valid UTF-8 but contains
characters that are not supported by the server as a value for that
string (e.g., names containing characters that have more than two
octets on a filesystem that supports Unicode characters only), the
server should return an NFS4ERR_BADCHAR error.
Where a UTF-8 string is used as a file name, and the filesystem,
while supporting all of the characters within the name, does not
allow that particular name to be used, the server should return the
error NFS4ERR_BADNAME. This includes situations in which the server
filesystem imposes a normalization constraint on name strings, but
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will also include such situations as filesystem prohibitions of "."
and ".." as file names for certain operations, and other such
constraints.
NFS error numbers are assigned to failed operations within a compound
request. A compound request contains a number of NFS operations that
have their results encoded in sequence in a compound reply. The
results of successful operations will consist of an NFS4_OK status
followed by the encoded results of the operation. If an NFS
operation fails, an error status will be entered in the reply and the
compound request will be terminated.
A description of each defined error follows:
NFS4_OK Indicates the operation completed successfully.
NFS4ERR_ACCESS Permission denied. The caller does not have the
correct permission to perform the requested
operation. Contrast this with NFS4ERR_PERM,
which restricts itself to owner or privileged
user permission failures.
NFS4ERR_ATTRNOTSUPP An attribute specified is not supported by the
server. Does not apply to the GETATTR
operation.
NFS4ERR_ADMIN_REVOKED Due to administrator intervention, the
lockowner's record locks, share reservations,
and delegations have been revoked by the
server.
NFS4ERR_BADCHAR A UTF-8 string contains a character which is
not supported by the server in the context in
which it being used.
NFS4ERR_BAD_COOKIE READDIR cookie is stale.
NFS4ERR_BADHANDLE Illegal NFS filehandle. The filehandle failed
internal consistency checks.
NFS4ERR_BADNAME A name string in a request consists of valid
UTF-8 characters supported by the server but
the name is not supported by the server as a
valid name for current operation.
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NFS4ERR_BADOWNER An owner, owner_group, or ACL attribute value
can not be translated to local representation.
NFS4ERR_BADTYPE An attempt was made to create an object of a
type not supported by the server.
NFS4ERR_BAD_RANGE The range for a LOCK, LOCKT, or LOCKU operation
is not appropriate to the allowable range of
offsets for the server.
NFS4ERR_BAD_SEQID The sequence number in a locking request is
neither the next expected number or the last
number processed.
NFS4ERR_BAD_STATEID A stateid generated by the current server
instance, but which does not designate any
locking state (either current or superseded)
for a current lockowner-file pair, was used.
NFS4ERR_BADXDR The server encountered an XDR decoding error
while processing an operation.
NFS4ERR_CLID_INUSE The SETCLIENTID operation has found that a
client id is already in use by another client.
NFS4ERR_DEADLOCK The server has been able to determine a file
locking deadlock condition for a blocking lock
request.
NFS4ERR_DELAY The server initiated the request, but was not
able to complete it in a timely fashion. The
client should wait and then try the request
with a new RPC transaction ID. For example,
this error should be returned from a server
that supports hierarchical storage and receives
a request to process a file that has been
migrated. In this case, the server should start
the immigration process and respond to client
with this error. This error may also occur
when a necessary delegation recall makes
processing a request in a timely fashion
impossible.
NFS4ERR_DENIED An attempt to lock a file is denied. Since
this may be a temporary condition, the client
is encouraged to retry the lock request until
the lock is accepted.
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NFS4ERR_DQUOT Resource (quota) hard limit exceeded. The
user's resource limit on the server has been
exceeded.
NFS4ERR_EXIST File exists. The file specified already exists.
NFS4ERR_EXPIRED A lease has expired that is being used in the
current operation.
NFS4ERR_FBIG File too large. The operation would have caused
a file to grow beyond the server's limit.
NFS4ERR_FHEXPIRED The filehandle provided is volatile and has
expired at the server.
NFS4ERR_FILE_OPEN The operation can not be successfully processed
because a file involved in the operation is
currently open.
NFS4ERR_GRACE The server is in its recovery or grace period
which should match the lease period of the
server.
NFS4ERR_INVAL Invalid argument or unsupported argument for an
operation. Two examples are attempting a
READLINK on an object other than a symbolic
link or specifying a value for an enum field
that is not defined in the protocol (e.g.,
nfs_ftype4).
NFS4ERR_IO I/O error. A hard error (for example, a disk
error) occurred while processing the requested
operation.
NFS4ERR_ISDIR Is a directory. The caller specified a
directory in a non-directory operation.
NFS4ERR_LEASE_MOVED A lease being renewed is associated with a
filesystem that has been migrated to a new
server.
NFS4ERR_LOCKED A read or write operation was attempted on a
locked file.
NFS4ERR_LOCK_NOTSUPP Server does not support atomic upgrade or
downgrade of locks.
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NFS4ERR_LOCK_RANGE A lock request is operating on a sub-range of a
current lock for the lock owner and the server
does not support this type of request.
NFS4ERR_LOCKS_HELD A CLOSE was attempted and file locks would
exist after the CLOSE.
NFS4ERR_MINOR_VERS_MISMATCH
The server has received a request that
specifies an unsupported minor version. The
server must return a COMPOUND4res with a zero
length operations result array.
NFS4ERR_MLINK Too many hard links.
NFS4ERR_MOVED The filesystem which contains the current
filehandle object has been relocated or
migrated to another server. The client may
obtain the new filesystem location by obtaining
the "fs_locations" attribute for the current
filehandle. For further discussion, refer to
the section "Filesystem Migration or
Relocation".
NFS4ERR_NAMETOOLONG The filename in an operation was too long.
NFS4ERR_NOENT No such file or directory. The file or
directory name specified does not exist.
NFS4ERR_NOFILEHANDLE The logical current filehandle value (or, in
the case of RESTOREFH, the saved filehandle
value) has not been set properly. This may be
a result of a malformed COMPOUND operation
(i.e., no PUTFH or PUTROOTFH before an
operation that requires the current filehandle
be set).
NFS4ERR_NO_GRACE A reclaim of client state has fallen outside of
the grace period of the server. As a result,
the server can not guarantee that conflicting
state has not been provided to another client.
NFS4ERR_NOSPC No space left on device. The operation would
have caused the server's filesystem to exceed
its limit.
NFS4ERR_NOTDIR Not a directory. The caller specified a non-
directory in a directory operation.
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NFS4ERR_NOTEMPTY An attempt was made to remove a directory that
was not empty.
NFS4ERR_NOTSUPP Operation is not supported.
NFS4ERR_NOT_SAME This error is returned by the VERIFY operation
to signify that the attributes compared were
not the same as provided in the client's
request.
NFS4ERR_NXIO I/O error. No such device or address.
NFS4ERR_OLD_STATEID A stateid which designates the locking state
for a lockowner-file at an earlier time was
used.
NFS4ERR_OPENMODE The client attempted a READ, WRITE, LOCK or
SETATTR operation not sanctioned by the stateid
passed (e.g., writing to a file opened only for
read).
NFS4ERR_OP_ILLEGAL An illegal operation value has been specified
in the argop field of a COMPOUND or CB_COMPOUND
procedure.
NFS4ERR_PERM Not owner. The operation was not allowed
because the caller is either not a privileged
user (root) or not the owner of the target of
the operation.
NFS4ERR_RECLAIM_BAD The reclaim provided by the client does not
match any of the server's state consistency
checks and is bad.
NFS4ERR_RECLAIM_CONFLICT
The reclaim provided by the client has
encountered a conflict and can not be provided.
Potentially indicates a misbehaving client.
NFS4ERR_RESOURCE For the processing of the COMPOUND procedure,
the server may exhaust available resources and
can not continue processing operations within
the COMPOUND procedure. This error will be
returned from the server in those instances of
resource exhaustion related to the processing
of the COMPOUND procedure.
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NFS4ERR_RESTOREFH The RESTOREFH operation does not have a saved
filehandle (identified by SAVEFH) to operate
upon.
NFS4ERR_ROFS Read-only filesystem. A modifying operation was
attempted on a read-only filesystem.
NFS4ERR_SAME This error is returned by the NVERIFY operation
to signify that the attributes compared were
the same as provided in the client's request.
NFS4ERR_SERVERFAULT An error occurred on the server which does not
map to any of the legal NFS version 4 protocol
error values. The client should translate this
into an appropriate error. UNIX clients may
choose to translate this to EIO.
NFS4ERR_SHARE_DENIED An attempt to OPEN a file with a share
reservation has failed because of a share
conflict.
NFS4ERR_STALE Invalid filehandle. The filehandle given in the
arguments was invalid. The file referred to by
that filehandle no longer exists or access to
it has been revoked.
NFS4ERR_STALE_CLIENTID A clientid not recognized by the server was
used in a locking or SETCLIENTID_CONFIRM
request.
NFS4ERR_STALE_STATEID A stateid generated by an earlier server
instance was used.
NFS4ERR_SYMLINK The current filehandle provided for a LOOKUP is
not a directory but a symbolic link. Also used
if the final component of the OPEN path is a
symbolic link.
NFS4ERR_TOOSMALL The encoded response to a READDIR request
exceeds the size limit set by the initial
request.
NFS4ERR_WRONGSEC The security mechanism being used by the client
for the operation does not match the server's
security policy. The client should change the
security mechanism being used and retry the
operation.
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NFS4ERR_XDEV Attempt to do an operation between different
fsids.
For the NFS version 4 RPC program, there are two traditional RPC
procedures: NULL and COMPOUND. All other functionality is defined as
a set of operations and these operations are defined in normal
XDR/RPC syntax and semantics. However, these operations are
encapsulated within the COMPOUND procedure. This requires that the
client combine one or more of the NFS version 4 operations into a
single request.
The NFS4_CALLBACK program is used to provide server to client
signaling and is constructed in a similar fashion as the NFS version
4 program. The procedures CB_NULL and CB_COMPOUND are defined in the
same way as NULL and COMPOUND are within the NFS program. The
CB_COMPOUND request also encapsulates the remaining operations of the
NFS4_CALLBACK program. There is no predefined RPC program number for
the NFS4_CALLBACK program. It is up to the client to specify a
program number in the "transient" program range. The program and
port number of the NFS4_CALLBACK program are provided by the client
as part of the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The program
and port can be changed by another SETCLIENTID/SETCLIENTID_CONFIRM
sequence, and it is possible to use the sequence to change them
within a client incarnation without removing relevant leased client
state.
The COMPOUND procedure provides the opportunity for better
performance within high latency networks. The client can avoid
cumulative latency of multiple RPCs by combining multiple dependent
operations into a single COMPOUND procedure. A compound operation
may provide for protocol simplification by allowing the client to
combine basic procedures into a single request that is customized for
the client's environment.
The CB_COMPOUND procedure precisely parallels the features of
COMPOUND as described above.
The basic structure of the COMPOUND procedure is:
+-----+--------------+--------+-----------+-----------+-----------+--
| tag | minorversion | numops | op + args | op + args | op + args |
+-----+--------------+--------+-----------+-----------+-----------+--
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and the reply's structure is:
+------------+-----+--------+-----------------------+--
|last status | tag | numres | status + op + results |
+------------+-----+--------+-----------------------+--
The numops and numres fields, used in the depiction above, represent
the count for the counted array encoding use to signify the number of
arguments or results encoded in the request and response. As per the
XDR encoding, these counts must match exactly the number of operation
arguments or results encoded.
The server will process the COMPOUND procedure by evaluating each of
the operations within the COMPOUND procedure in order. Each
component operation consists of a 32 bit operation code, followed by
the argument of length determined by the type of operation. The
results of each operation are encoded in sequence into a reply
buffer. The results of each operation are preceded by the opcode and
a status code (normally zero). If an operation results in a non-zero
status code, the status will be encoded and evaluation of the
compound sequence will halt and the reply will be returned. Note
that evaluation stops even in the event of "non error" conditions
such as NFS4ERR_SAME.
There are no atomicity requirements for the operations contained
within the COMPOUND procedure. The operations being evaluated as
part of a COMPOUND request may be evaluated simultaneously with other
COMPOUND requests that the server receives.
It is the client's responsibility for recovering from any partially
completed COMPOUND procedure. Partially completed COMPOUND
procedures may occur at any point due to errors such as
NFS4ERR_RESOURCE and NFS4ERR_DELAY. This may occur even given an
otherwise valid operation string. Further, a server reboot which
occurs in the middle of processing a COMPOUND procedure may leave the
client with the difficult task of determining how far COMPOUND
processing has proceeded. Therefore, the client should avoid overly
complex COMPOUND procedures in the event of the failure of an
operation within the procedure.
Each operation assumes a "current" and "saved" filehandle that is
available as part of the execution context of the compound request.
Operations may set, change, or return the current filehandle. The
"saved" filehandle is used for temporary storage of a filehandle
value and as operands for the RENAME and LINK operations.
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RFC 3530 NFS version 4 Protocol April 2003
NFS version 4 operations that modify the filesystem are synchronous.
When an operation is successfully completed at the server, the client
can depend that any data associated with the request is now on stable
storage (the one exception is in the case of the file data in a WRITE
operation with the UNSTABLE option specified).
This implies that any previous operations within the same compound
request are also reflected in stable storage. This behavior enables
the client's ability to recover from a partially executed compound
request which may resulted from the failure of the server. For
example, if a compound request contains operations A and B and the
server is unable to send a response to the client, depending on the
progress the server made in servicing the request the result of both
operations may be reflected in stable storage or just operation A may
be reflected. The server must not have just the results of operation
B in stable storage.
The operations encoded in the COMPOUND procedure are identified by
operation values. To avoid overlap with the RPC procedure numbers,
operations 0 (zero) and 1 are not defined. Operation 2 is not
defined but reserved for future use with minor versioning.
SYNOPSIS
<null>
ARGUMENT
void;
RESULT
void;
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DESCRIPTION
Standard NULL procedure. Void argument, void response. This
procedure has no functionality associated with it. Because of
this it is sometimes used to measure the overhead of processing a
service request. Therefore, the server should ensure that no
unnecessary work is done in servicing this procedure.
ERRORS
None.
SYNOPSIS
compoundargs -> compoundres
ARGUMENT
union nfs_argop4 switch (nfs_opnum4 argop) {
case <OPCODE>: <argument>;
...
};
struct COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
RESULT
union nfs_resop4 switch (nfs_opnum4 resop){
case <OPCODE>: <result>;
...
};
struct COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_resop4 resarray<>;
};
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DESCRIPTION
The COMPOUND procedure is used to combine one or more of the NFS
operations into a single RPC request. The main NFS RPC program has
two main procedures: NULL and COMPOUND. All other operations use the
COMPOUND procedure as a wrapper.
The COMPOUND procedure is used to combine individual operations into
a single RPC request. The server interprets each of the operations
in turn. If an operation is executed by the server and the status of
that operation is NFS4_OK, then the next operation in the COMPOUND
procedure is executed. The server continues this process until there
are no more operations to be executed or one of the operations has a
status value other than NFS4_OK.
In the processing of the COMPOUND procedure, the server may find that
it does not have the available resources to execute any or all of the
operations within the COMPOUND sequence. In this case, the error
NFS4ERR_RESOURCE will be returned for the particular operation within
the COMPOUND procedure where the resource exhaustion occurred. This
assumes that all previous operations within the COMPOUND sequence
have been evaluated successfully. The results for all of the
evaluated operations must be returned to the client.
The server will generally choose between two methods of decoding the
client's request. The first would be the traditional one-pass XDR
decode, in which decoding of the entire COMPOUND precedes execution
of any operation within it. If there is an XDR decoding error in
this case, an RPC XDR decode error would be returned. The second
method would be to make an initial pass to decode the basic COMPOUND
request and then to XDR decode each of the individual operations, as
the server is ready to execute it. In this case, the server may
encounter an XDR decode error during such an operation decode, after
previous operations within the COMPOUND have been executed. In this
case, the server would return the error NFS4ERR_BADXDR to signify the
decode error.
The COMPOUND arguments contain a "minorversion" field. The initial
and default value for this field is 0 (zero). This field will be
used by future minor versions such that the client can communicate to
the server what minor version is being requested. If the server
receives a COMPOUND procedure with a minorversion field value that it
does not support, the server MUST return an error of
NFS4ERR_MINOR_VERS_MISMATCH and a zero length resultdata array.
Contained within the COMPOUND results is a "status" field. If the
results array length is non-zero, this status must be equivalent to
the status of the last operation that was executed within the
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RFC 3530 NFS version 4 Protocol April 2003
COMPOUND procedure. Therefore, if an operation incurred an error
then the "status" value will be the same error value as is being
returned for the operation that failed.
Note that operations, 0 (zero) and 1 (one) are not defined for the
COMPOUND procedure. Operation 2 is not defined but reserved for
future definition and use with minor versioning. If the server
receives a operation array that contains operation 2 and the
minorversion field has a value of 0 (zero), an error of
NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned
to the client. If an operation array contains an operation 2 and the
minorversion field is non-zero and the server does not support the
minor version, the server returns an error of
NFS4ERR_MINOR_VERS_MISMATCH. Therefore, the
NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
errors.
It is possible that the server receives a request that contains an
operation that is less than the first legal operation (OP_ACCESS) or
greater than the last legal operation (OP_RELEASE_LOCKOWNER).
In this case, the server's response will encode the opcode OP_ILLEGAL
rather than the illegal opcode of the request. The status field in
the ILLEGAL return results will set to NFS4ERR_OP_ILLEGAL. The
COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.
The definition of the "tag" in the request is left to the
implementor. It may be used to summarize the content of the compound
request for the benefit of packet sniffers and engineers debugging
implementations. However, the value of "tag" in the response SHOULD
be the same value as provided in the request. This applies to the
tag field of the CB_COMPOUND procedure as well.
IMPLEMENTATION
Since an error of any type may occur after only a portion of the
operations have been evaluated, the client must be prepared to
recover from any failure. If the source of an NFS4ERR_RESOURCE error
was a complex or lengthy set of operations, it is likely that if the
number of operations were reduced the server would be able to
evaluate them successfully. Therefore, the client is responsible for
dealing with this type of complexity in recovery.
ERRORS
All errors defined in the protocol
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SYNOPSIS
(cfh), accessreq -> supported, accessrights
ARGUMENT
const ACCESS4_READ = 0x00000001;
const ACCESS4_LOOKUP = 0x00000002;
const ACCESS4_MODIFY = 0x00000004;
const ACCESS4_EXTEND = 0x00000008;
const ACCESS4_DELETE = 0x00000010;
const ACCESS4_EXECUTE = 0x00000020;
struct ACCESS4args {
/* CURRENT_FH: object */
uint32_t access;
};
RESULT
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
DESCRIPTION
ACCESS determines the access rights that a user, as identified by the
credentials in the RPC request, has with respect to the file system
object specified by the current filehandle. The client encodes the
set of access rights that are to be checked in the bit mask "access".
The server checks the permissions encoded in the bit mask. If a
status of NFS4_OK is returned, two bit masks are included in the
response. The first, "supported", represents the access rights for
which the server can verify reliably. The second, "access",
represents the access rights available to the user for the filehandle
provided. On success, the current filehandle retains its value.
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Note that the supported field will contain only as many values as
were originally sent in the arguments. For example, if the client
sends an ACCESS operation with only the ACCESS4_READ value set and
the server supports this value, the server will return only
ACCESS4_READ even if it could have reliably checked other values.
The results of this operation are necessarily advisory in nature. A
return status of NFS4_OK and the appropriate bit set in the bit mask
does not imply that such access will be allowed to the file system
object in the future. This is because access rights can be revoked by
the server at any time.
The following access permissions may be requested:
ACCESS4_READ Read data from file or read a directory.
ACCESS4_LOOKUP Look up a name in a directory (no meaning for non-
directory objects).
ACCESS4_MODIFY Rewrite existing file data or modify existing
directory entries.
ACCESS4_EXTEND Write new data or add directory entries.
ACCESS4_DELETE Delete an existing directory entry.
ACCESS4_EXECUTE Execute file (no meaning for a directory).
On success, the current filehandle retains its value.
IMPLEMENTATION
In general, it is not sufficient for the client to attempt to deduce
access permissions by inspecting the uid, gid, and mode fields in the
file attributes or by attempting to interpret the contents of the ACL
attribute. This is because the server may perform uid or gid mapping
or enforce additional access control restrictions. It is also
possible that the server may not be in the same ID space as the
client. In these cases (and perhaps others), the client can not
reliably perform an access check with only current file attributes.
In the NFS version 2 protocol, the only reliable way to determine
whether an operation was allowed was to try it and see if it
succeeded or failed. Using the ACCESS operation in the NFS version 4
protocol, the client can ask the server to indicate whether or not
one or more classes of operations are permitted. The ACCESS
operation is provided to allow clients to check before doing a series
of operations which will result in an access failure. The OPEN
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RFC 3530 NFS version 4 Protocol April 2003
operation provides a point where the server can verify access to the
file object and method to return that information to the client. The
ACCESS operation is still useful for directory operations or for use
in the case the UNIX API "access" is used on the client.
The information returned by the server in response to an ACCESS call
is not permanent. It was correct at the exact time that the server
performed the checks, but not necessarily afterwards. The server can
revoke access permission at any time.
The client should use the effective credentials of the user to build
the authentication information in the ACCESS request used to
determine access rights. It is the effective user and group
credentials that are used in subsequent read and write operations.
Many implementations do not directly support the ACCESS4_DELETE
permission. Operating systems like UNIX will ignore the
ACCESS4_DELETE bit if set on an access request on a non-directory
object. In these systems, delete permission on a file is determined
by the access permissions on the directory in which the file resides,
instead of being determined by the permissions of the file itself.
Therefore, the mask returned enumerating which access rights can be
determined will have the ACCESS4_DELETE value set to 0. This
indicates to the client that the server was unable to check that
particular access right. The ACCESS4_DELETE bit in the access mask
returned will then be ignored by the client.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), seqid, open_stateid -> open_stateid
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ARGUMENT
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid
stateid4 open_stateid;
};
RESULT
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
DESCRIPTION
The CLOSE operation releases share reservations for the regular or
named attribute file as specified by the current filehandle. The
share reservations and other state information released at the server
as a result of this CLOSE is only associated with the supplied
stateid. The sequence id provides for the correct ordering. State
associated with other OPENs is not affected.
If record locks are held, the client SHOULD release all locks before
issuing a CLOSE. The server MAY free all outstanding locks on CLOSE
but some servers may not support the CLOSE of a file that still has
record locks held. The server MUST return failure if any locks would
exist after the CLOSE.
On success, the current filehandle retains its value.
IMPLEMENTATION
Even though CLOSE returns a stateid, this stateid is not useful to
the client and should be treated as deprecated. CLOSE "shuts down"
the state associated with all OPENs for the file by a single
open_owner. As noted above, CLOSE will either release all file
locking state or return an error. Therefore, the stateid returned by
CLOSE is not useful for operations that follow.
ERRORS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
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NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCKS_HELD
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
SYNOPSIS
(cfh), offset, count -> verifier
ARGUMENT
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
RESULT
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
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DESCRIPTION
The COMMIT operation forces or flushes data to stable storage for the
file specified by the current filehandle. The flushed data is that
which was previously written with a WRITE operation which had the
stable field set to UNSTABLE4.
The offset specifies the position within the file where the flush is
to begin. An offset value of 0 (zero) means to flush data starting
at the beginning of the file. The count specifies the number of
bytes of data to flush. If count is 0 (zero), a flush from offset to
the end of the file is done.
The server returns a write verifier upon successful completion of the
COMMIT. The write verifier is used by the client to determine if the
server has restarted or rebooted between the initial WRITE(s) and the
COMMIT. The client does this by comparing the write verifier
returned from the initial writes and the verifier returned by the
COMMIT operation. The server must vary the value of the write
verifier at each server event or instantiation that may lead to a
loss of uncommitted data. Most commonly this occurs when the server
is rebooted; however, other events at the server may result in
uncommitted data loss as well.
On success, the current filehandle retains its value.
IMPLEMENTATION
The COMMIT operation is similar in operation and semantics to the
POSIX fsync(2) system call that synchronizes a file's state with the
disk (file data and metadata is flushed to disk or stable storage).
COMMIT performs the same operation for a client, flushing any
unsynchronized data and metadata on the server to the server's disk
or stable storage for the specified file. Like fsync(2), it may be
that there is some modified data or no modified data to synchronize.
The data may have been synchronized by the server's normal periodic
buffer synchronization activity. COMMIT should return NFS4_OK,
unless there has been an unexpected error.
COMMIT differs from fsync(2) in that it is possible for the client to
flush a range of the file (most likely triggered by a buffer-
reclamation scheme on the client before file has been completely
written).
The server implementation of COMMIT is reasonably simple. If the
server receives a full file COMMIT request, that is starting at
offset 0 and count 0, it should do the equivalent of fsync()'ing the
file. Otherwise, it should arrange to have the cached data in the
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range specified by offset and count to be flushed to stable storage.
In both cases, any metadata associated with the file must be flushed
to stable storage before returning. It is not an error for there to
be nothing to flush on the server. This means that the data and
metadata that needed to be flushed have already been flushed or lost
during the last server failure.
The client implementation of COMMIT is a little more complex. There
are two reasons for wanting to commit a client buffer to stable
storage. The first is that the client wants to reuse a buffer. In
this case, the offset and count of the buffer are sent to the server
in the COMMIT request. The server then flushes any cached data based
on the offset and count, and flushes any metadata associated with the
file. It then returns the status of the flush and the write
verifier. The other reason for the client to generate a COMMIT is
for a full file flush, such as may be done at close. In this case,
the client would gather all of the buffers for this file that contain
uncommitted data, do the COMMIT operation with an offset of 0 and
count of 0, and then free all of those buffers. Any other dirty
buffers would be sent to the server in the normal fashion.
After a buffer is written by the client with the stable parameter set
to UNSTABLE4, the buffer must be considered as modified by the client
until the buffer has either been flushed via a COMMIT operation or
written via a WRITE operation with stable parameter set to FILE_SYNC4
or DATA_SYNC4. This is done to prevent the buffer from being freed
and reused before the data can be flushed to stable storage on the
server.
When a response is returned from either a WRITE or a COMMIT operation
and it contains a write verifier that is different than previously
returned by the server, the client will need to retransmit all of the
buffers containing uncommitted cached data to the server. How this
is to be done is up to the implementor. If there is only one buffer
of interest, then it should probably be sent back over in a WRITE
request with the appropriate stable parameter. If there is more than
one buffer, it might be worthwhile retransmitting all of the buffers
in WRITE requests with the stable parameter set to UNSTABLE4 and then
retransmitting the COMMIT operation to flush all of the data on the
server to stable storage. The timing of these retransmissions is
left to the implementor.
The above description applies to page-cache-based systems as well as
buffer-cache-based systems. In those systems, the virtual memory
system will need to be modified instead of the buffer cache.
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ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), name, type, attrs -> (cfh), change_info, attrs_set
ARGUMENT
union createtype4 switch (nfs_ftype4 type) {
case NF4LNK:
linktext4 linkdata;
case NF4BLK:
case NF4CHR:
specdata4 devdata;
case NF4SOCK:
case NF4FIFO:
case NF4DIR:
void;
};
struct CREATE4args {
/* CURRENT_FH: directory for creation */
createtype4 objtype;
component4 objname;
fattr4 createattrs;
};
RESULT
struct CREATE4resok {
change_info4 cinfo;
bitmap4 attrset; /* attributes set */
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};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
DESCRIPTION
The CREATE operation creates a non-regular file object in a directory
with a given name. The OPEN operation MUST be used to create a
regular file.
The objname specifies the name for the new object. The objtype
determines the type of object to be created: directory, symlink, etc.
If an object of the same name already exists in the directory, the
server will return the error NFS4ERR_EXIST.
For the directory where the new file object was created, the server
returns change_info4 information in cinfo. With the atomic field of
the change_info4 struct, the server will indicate if the before and
after change attributes were obtained atomically with respect to the
file object creation.
If the objname has a length of 0 (zero), or if objname does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
The current filehandle is replaced by that of the new object.
The createattrs specifies the initial set of attributes for the
object. The set of attributes may include any writable attribute
valid for the object type. When the operation is successful, the
server will return to the client an attribute mask signifying which
attributes were successfully set for the object.
If createattrs includes neither the owner attribute nor an ACL with
an ACE for the owner, and if the server's filesystem both supports
and requires an owner attribute (or an owner ACE) then the server
MUST derive the owner (or the owner ACE). This would typically be
from the principal indicated in the RPC credentials of the call, but
the server's operating environment or filesystem semantics may
dictate other methods of derivation. Similarly, if createattrs
includes neither the group attribute nor a group ACE, and if the
server's filesystem both supports and requires the notion of a group
attribute (or group ACE), the server MUST derive the group attribute
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(or the corresponding owner ACE) for the file. This could be from the
RPC call's credentials, such as the group principal if the
credentials include it (such as with AUTH_SYS), from the group
identifier associated with the principal in the credentials (for
e.g., POSIX systems have a passwd database that has the group
identifier for every user identifier), inherited from directory the
object is created in, or whatever else the server's operating
environment or filesystem semantics dictate. This applies to the OPEN
operation too.
Conversely, it is possible the client will specify in createattrs an
owner attribute or group attribute or ACL that the principal
indicated the RPC call's credentials does not have permissions to
create files for. The error to be returned in this instance is
NFS4ERR_PERM. This applies to the OPEN operation too.
IMPLEMENTATION
If the client desires to set attribute values after the create, a
SETATTR operation can be added to the COMPOUND request so that the
appropriate attributes will be set.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ATTRNOTSUPP
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADOWNER
NFS4ERR_BADTYPE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_PERM
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
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SYNOPSIS
clientid ->
ARGUMENT
struct DELEGPURGE4args {
clientid4 clientid;
};
RESULT
struct DELEGPURGE4res {
nfsstat4 status;
};
DESCRIPTION
Purges all of the delegations awaiting recovery for a given client.
This is useful for clients which do not commit delegation information
to stable storage to indicate that conflicting requests need not be
delayed by the server awaiting recovery of delegation information.
This operation should be used by clients that record delegation
information on stable storage on the client. In this case,
DELEGPURGE should be issued immediately after doing delegation
recovery on all delegations known to the client. Doing so will
notify the server that no additional delegations for the client will
be recovered allowing it to free resources, and avoid delaying other
clients who make requests that conflict with the unrecovered
delegations. The set of delegations known to the server and the
client may be different. The reason for this is that a client may
fail after making a request which resulted in delegation but before
it received the results and committed them to the client's stable
storage.
The server MAY support DELEGPURGE, but if it does not, it MUST NOT
support CLAIM_DELEGATE_PREV.
ERRORS
NFS4ERR_BADXDR
NFS4ERR_NOTSUPP
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_RESOURCE
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NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
SYNOPSIS
(cfh), stateid ->
ARGUMENT
struct DELEGRETURN4args {
/* CURRENT_FH: delegated file */
stateid4 stateid;
};
RESULT
struct DELEGRETURN4res {
nfsstat4 status;
};
DESCRIPTION
Returns the delegation represented by the current filehandle and
stateid.
Delegations may be returned when recalled or voluntarily (i.e.,
before the server has recalled them). In either case the client must
properly propagate state changed under the context of the delegation
to the server before returning the delegation.
ERRORS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_EXPIRED
NFS4ERR_INVAL
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
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SYNOPSIS
(cfh), attrbits -> attrbits, attrvals
ARGUMENT
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
RESULT
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
DESCRIPTION
The GETATTR operation will obtain attributes for the filesystem
object specified by the current filehandle. The client sets a bit in
the bitmap argument for each attribute value that it would like the
server to return. The server returns an attribute bitmap that
indicates the attribute values for which it was able to return,
followed by the attribute values ordered lowest attribute number
first.
The server must return a value for each attribute that the client
requests if the attribute is supported by the server. If the server
does not support an attribute or cannot approximate a useful value
then it must not return the attribute value and must not set the
attribute bit in the result bitmap. The server must return an error
if it supports an attribute but cannot obtain its value. In that
case no attribute values will be returned.
All servers must support the mandatory attributes as specified in the
section "File Attributes".
On success, the current filehandle retains its value.
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IMPLEMENTATION
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh) -> filehandle
ARGUMENT
/* CURRENT_FH: */
void;
RESULT
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
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IMPLEMENTATION
Operations that change the current filehandle like LOOKUP or CREATE
do not automatically return the new filehandle as a result. For
instance, if a client needs to lookup a directory entry and obtain
its filehandle then the following request is needed.
PUTFH (directory filehandle)
LOOKUP (entry name)
GETFH
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(sfh), (cfh), newname -> (cfh), change_info
ARGUMENT
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
RESULT
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
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DESCRIPTION
The LINK operation creates an additional newname for the file
represented by the saved filehandle, as set by the SAVEFH operation,
in the directory represented by the current filehandle. The existing
file and the target directory must reside within the same filesystem
on the server. On success, the current filehandle will continue to
be the target directory. If an object exists in the target directory
with the same name as newname, the server must return NFS4ERR_EXIST.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 struct, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the link creation.
If the newname has a length of 0 (zero), or if newname does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
IMPLEMENTATION
Changes to any property of the "hard" linked files are reflected in
all of the linked files. When a link is made to a file, the
attributes for the file should have a value for numlinks that is one
greater than the value before the LINK operation.
The statement "file and the target directory must reside within the
same filesystem on the server" means that the fsid fields in the
attributes for the objects are the same. If they reside on different
filesystems, the error, NFS4ERR_XDEV, is returned. On some servers,
the filenames, "." and "..", are illegal as newname.
In the case that newname is already linked to the file represented by
the saved filehandle, the server will return NFS4ERR_EXIST.
Note that symbolic links are created with the CREATE operation.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_FILE_OPEN
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NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_MLINK
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
NFS4ERR_XDEV
SYNOPSIS
(cfh) locktype, reclaim, offset, length, locker -> stateid
ARGUMENT
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
struct exist_lock_owner4 {
stateid4 lock_stateid;
seqid4 lock_seqid;
};
union locker4 switch (bool new_lock_owner) {
case TRUE:
open_to_lock_owner4 open_owner;
case FALSE:
exist_lock_owner4 lock_owner;
};
enum nfs_lock_type4 {
READ_LT = 1,
WRITE_LT = 2,
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READW_LT = 3, /* blocking read */
WRITEW_LT = 4 /* blocking write */
};
struct LOCK4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
bool reclaim;
offset4 offset;
length4 length;
locker4 locker;
};
RESULT
struct LOCK4denied {
offset4 offset;
length4 length;
nfs_lock_type4 locktype;
lock_owner4 owner;
};
struct LOCK4resok {
stateid4 lock_stateid;
};
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
LOCK4resok resok4;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
void;
};
DESCRIPTION
The LOCK operation requests a record lock for the byte range
specified by the offset and length parameters. The lock type is also
specified to be one of the nfs_lock_type4s. If this is a reclaim
request, the reclaim parameter will be TRUE;
Bytes in a file may be locked even if those bytes are not currently
allocated to the file. To lock the file from a specific offset
through the end-of-file (no matter how long the file actually is) use
a length field with all bits set to 1 (one). If the length is zero,
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RFC 3530 NFS version 4 Protocol April 2003
or if a length which is not all bits set to one is specified, and
length when added to the offset exceeds the maximum 64-bit unsigned
integer value, the error NFS4ERR_INVAL will result.
Some servers may only support locking for byte offsets that fit
within 32 bits. If the client specifies a range that includes a byte
beyond the last byte offset of the 32-bit range, but does not include
the last byte offset of the 32-bit and all of the byte offsets beyond
it, up to the end of the valid 64-bit range, such a 32-bit server
MUST return the error NFS4ERR_BAD_RANGE.
In the case that the lock is denied, the owner, offset, and length of
a conflicting lock are returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
If the server is unable to determine the exact offset and length of
the conflicting lock, the same offset and length that were provided
in the arguments should be returned in the denied results. The File
Locking section contains a full description of this and the other
file locking operations.
LOCK operations are subject to permission checks and to checks
against the access type of the associated file. However, the
specific right and modes required for various type of locks, reflect
the semantics of the server-exported filesystem, and are not
specified by the protocol. For example, Windows 2000 allows a write
lock of a file open for READ, while a POSIX-compliant system does
not.
When the client makes a lock request that corresponds to a range that
the lockowner has locked already (with the same or different lock
type), or to a sub-region of such a range, or to a region which
includes multiple locks already granted to that lockowner, in whole
or in part, and the server does not support such locking operations
(i.e., does not support POSIX locking semantics), the server will
return the error NFS4ERR_LOCK_RANGE. In that case, the client may
return an error, or it may emulate the required operations, using
only LOCK for ranges that do not include any bytes already locked by
that lock_owner and LOCKU of locks held by that lock_owner
(specifying an exactly-matching range and type). Similarly, when the
client makes a lock request that amounts to upgrading (changing from
a read lock to a write lock) or downgrading (changing from write lock
to a read lock) an existing record lock, and the server does not
Shepler, et al. Standards Track [Page 158]
RFC 3530 NFS version 4 Protocol April 2003
support such a lock, the server will return NFS4ERR_LOCK_NOTSUPP.
Such operations may not perfectly reflect the required semantics in
the face of conflicting lock requests from other clients.
The locker argument specifies the lock_owner that is associated with
the LOCK request. The locker4 structure is a switched union that
indicates whether the lock_owner is known to the server or if the
lock_owner is new to the server. In the case that the lock_owner is
known to the server and has an established lock_seqid, the argument
is just the lock_owner and lock_seqid. In the case that the
lock_owner is not known to the server, the argument contains not only
the lock_owner and lock_seqid but also the open_stateid and
open_seqid. The new lock_owner case covers the very first lock done
by the lock_owner and offers a method to use the established state of
the open_stateid to transition to the use of the lock_owner.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_RANGE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_DEADLOCK
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCK_NOTSUPP
NFS4ERR_LOCK_RANGE
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NO_GRACE
NFS4ERR_OLD_STATEID
NFS4ERR_OPENMODE
NFS4ERR_RECLAIM_BAD
NFS4ERR_RECLAIM_CONFLICT
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_CLIENTID
NFS4ERR_STALE_STATEID
Shepler, et al. Standards Track [Page 159]
RFC 3530 NFS version 4 Protocol April 2003
SYNOPSIS
(cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
owner}
ARGUMENT
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
RESULT
struct LOCK4denied {
offset4 offset;
length4 length;
nfs_lock_type4 locktype;
lock_owner4 owner;
};
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
DESCRIPTION
The LOCKT operation tests the lock as specified in the arguments. If
a conflicting lock exists, the owner, offset, length, and type of the
conflicting lock are returned; if no lock is held, nothing other than
NFS4_OK is returned. Lock types READ_LT and READW_LT are processed
in the same way in that a conflicting lock test is done without
regard to blocking or non-blocking. The same is true for WRITE_LT
and WRITEW_LT.
The ranges are specified as for LOCK. The NFS4ERR_INVAL and
NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
for LOCK.
Shepler, et al. Standards Track [Page 160]
RFC 3530 NFS version 4 Protocol April 2003
On success, the current filehandle retains its value.
IMPLEMENTATION
If the server is unable to determine the exact offset and length of
the conflicting lock, the same offset and length that were provided
in the arguments should be returned in the denied results. The File
Locking section contains further discussion of the file locking
mechanisms.
LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
identify the owner. This is because the client does not have to open
the file to test for the existence of a lock, so a stateid may not be
available.
The test for conflicting locks should exclude locks for the current
lockowner. Note that since such locks are not examined the possible
existence of overlapping ranges may not affect the results of LOCKT.
If the server does examine locks that match the lockowner for the
purpose of range checking, NFS4ERR_LOCK_RANGE may be returned.. In
the event that it returns NFS4_OK, clients may do a LOCK and receive
NFS4ERR_LOCK_RANGE on the LOCK request because of the flexibility
provided to the server.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_RANGE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCK_RANGE
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_CLIENTID
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SYNOPSIS
(cfh) type, seqid, stateid, offset, length -> stateid
ARGUMENT
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 stateid;
offset4 offset;
length4 length;
};
RESULT
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
default:
void;
};
DESCRIPTION
The LOCKU operation unlocks the record lock specified by the
parameters. The client may set the locktype field to any value that
is legal for the nfs_lock_type4 enumerated type, and the server MUST
accept any legal value for locktype. Any legal value for locktype has
no effect on the success or failure of the LOCKU operation.
The ranges are specified as for LOCK. The NFS4ERR_INVAL and
NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
for LOCK.
On success, the current filehandle retains its value.
IMPLEMENTATION
If the area to be unlocked does not correspond exactly to a lock
actually held by the lockowner the server may return the error
NFS4ERR_LOCK_RANGE. This includes the case in which the area is not
locked, where the area is a sub-range of the area locked, where it
overlaps the area locked without matching exactly or the area
specified includes multiple locks held by the lockowner. In all of
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RFC 3530 NFS version 4 Protocol April 2003
these cases, allowed by POSIX locking semantics, a client receiving
this error, should if it desires support for such operations,
simulate the operation using LOCKU on ranges corresponding to locks
it actually holds, possibly followed by LOCK requests for the sub-
ranges not being unlocked.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_RANGE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCK_RANGE
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
SYNOPSIS
(cfh), component -> (cfh)
ARGUMENT
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
Shepler, et al. Standards Track [Page 163]
RFC 3530 NFS version 4 Protocol April 2003
RESULT
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
DESCRIPTION
This operation LOOKUPs or finds a filesystem object using the
directory specified by the current filehandle. LOOKUP evaluates the
component and if the object exists the current filehandle is replaced
with the component's filehandle.
If the component cannot be evaluated either because it does not exist
or because the client does not have permission to evaluate the
component, then an error will be returned and the current filehandle
will be unchanged.
If the component is a zero length string or if any component does not
obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
IMPLEMENTATION
If the client wants to achieve the effect of a multi-component
lookup, it may construct a COMPOUND request such as (and obtain each
filehandle):
PUTFH (directory filehandle)
LOOKUP "pub"
GETFH
LOOKUP "foo"
GETFH
LOOKUP "bar"
GETFH
NFS version 4 servers depart from the semantics of previous NFS
versions in allowing LOOKUP requests to cross mountpoints on the
server. The client can detect a mountpoint crossing by comparing the
fsid attribute of the directory with the fsid attribute of the
directory looked up. If the fsids are different then the new
directory is a server mountpoint. UNIX clients that detect a
mountpoint crossing will need to mount the server's filesystem. This
needs to be done to maintain the file object identity checking
mechanisms common to UNIX clients.
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RFC 3530 NFS version 4 Protocol April 2003
Servers that limit NFS access to "shares" or "exported" filesystems
should provide a pseudo-filesystem into which the exported
filesystems can be integrated, so that clients can browse the
server's name space. The clients' view of a pseudo filesystem will
be limited to paths that lead to exported filesystems.
Note: previous versions of the protocol assigned special semantics to
the names "." and "..". NFS version 4 assigns no special semantics
to these names. The LOOKUPP operator must be used to lookup a parent
directory.
Note that this operation does not follow symbolic links. The client
is responsible for all parsing of filenames including filenames that
are modified by symbolic links encountered during the lookup process.
If the current filehandle supplied is not a directory but a symbolic
link, the error NFS4ERR_SYMLINK is returned as the error. For all
other non-directory file types, the error NFS4ERR_NOTDIR is returned.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADXDR
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_SYMLINK
NFS4ERR_WRONGSEC
SYNOPSIS
(cfh) -> (cfh)
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ARGUMENT
/* CURRENT_FH: object */
void;
RESULT
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
DESCRIPTION
The current filehandle is assumed to refer to a regular directory
or a named attribute directory. LOOKUPP assigns the filehandle for
its parent directory to be the current filehandle. If there is no
parent directory an NFS4ERR_NOENT error must be returned.
Therefore, NFS4ERR_NOENT will be returned by the server when the
current filehandle is at the root or top of the server's file tree.
IMPLEMENTATION
As for LOOKUP, LOOKUPP will also cross mountpoints.
If the current filehandle is not a directory or named attribute
directory, the error NFS4ERR_NOTDIR is returned.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), fattr -> -
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ARGUMENT
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
RESULT
struct NVERIFY4res {
nfsstat4 status;
};
DESCRIPTION
This operation is used to prefix a sequence of operations to be
performed if one or more attributes have changed on some filesystem
object. If all the attributes match then the error NFS4ERR_SAME must
be returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
This operation is useful as a cache validation operator. If the
object to which the attributes belong has changed then the following
operations may obtain new data associated with that object. For
instance, to check if a file has been changed and obtain new data if
it has:
PUTFH (public)
LOOKUP "foobar"
NVERIFY attrbits attrs
READ 0 32767
In the case that a recommended attribute is specified in the NVERIFY
operation and the server does not support that attribute for the
filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
client.
When the attribute rdattr_error or any write-only attribute (e.g.,
time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
the client.
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ERRORS
NFS4ERR_ACCESS
NFS4ERR_ATTRNOTSUPP
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SAME
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), seqid, share_access, share_deny, owner, openhow, claim ->
(cfh), stateid, cinfo, rflags, open_confirm, attrset delegation
ARGUMENT
struct OPEN4args {
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
open_owner4 owner;
openflag4 openhow;
open_claim4 claim;
};
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
EXCLUSIVE4 = 2
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
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};
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
default:
void;
};
/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3
};
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RFC 3530 NFS version 4 Protocol April 2003
struct open_claim_delegate_cur4 {
stateid4 delegate_stateid;
component4 file;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file. Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
component4 file;
/*
* Right to the file established by an open previous to server
* reboot. File identified by filehandle obtained at that time
* rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
open_delegation_type4 delegate_type;
/*
* Right to file based on a delegation granted by the server.
* File is specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/* Right to file based on a delegation granted to a previous boot
* instance of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
/* CURRENT_FH: directory */
component4 file_delegate_prev;
};
RESULT
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
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RFC 3530 NFS version 4 Protocol April 2003
open for read */
};
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4 space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close.
*/
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
part of a delegated
open. */
};
union open_delegation4
switch (open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
};
const OPEN4_RESULT_CONFIRM = 0x00000002;
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
bitmap4 attrset; /* attributes on create */
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
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void;
};
WARNING TO CLIENT IMPLEMENTORS
OPEN resembles LOOKUP in that it generates a filehandle for the
client to use. Unlike LOOKUP though, OPEN creates server state on
the filehandle. In normal circumstances, the client can only release
this state with a CLOSE operation. CLOSE uses the current filehandle
to determine which file to close. Therefore the client MUST follow
every OPEN operation with a GETFH operation in the same COMPOUND
procedure. This will supply the client with the filehandle such that
CLOSE can be used appropriately.
Simply waiting for the lease on the file to expire is insufficient
because the server may maintain the state indefinitely as long as
another client does not attempt to make a conflicting access to the
same file.
DESCRIPTION
The OPEN operation creates and/or opens a regular file in a directory
with the provided name. If the file does not exist at the server and
creation is desired, specification of the method of creation is
provided by the openhow parameter. The client has the choice of
three creation methods: UNCHECKED, GUARDED, or EXCLUSIVE.
If the current filehandle is a named attribute directory, OPEN will
then create or open a named attribute file. Note that exclusive
create of a named attribute is not supported. If the createmode is
EXCLUSIVE4 and the current filehandle is a named attribute directory,
the server will return EINVAL.
UNCHECKED means that the file should be created if a file of that
name does not exist and encountering an existing regular file of that
name is not an error. For this type of create, createattrs specifies
the initial set of attributes for the file. The set of attributes
may include any writable attribute valid for regular files. When an
UNCHECKED create encounters an existing file, the attributes
specified by createattrs are not used, except that when an size of
zero is specified, the existing file is truncated. If GUARDED is
specified, the server checks for the presence of a duplicate object
by name before performing the create. If a duplicate exists, an
error of NFS4ERR_EXIST is returned as the status. If the object does
not exist, the request is performed as described for UNCHECKED. For
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RFC 3530 NFS version 4 Protocol April 2003
each of these cases (UNCHECKED and GUARDED) where the operation is
successful, the server will return to the client an attribute mask
signifying which attributes were successfully set for the object.
EXCLUSIVE specifies that the server is to follow exclusive creation
semantics, using the verifier to ensure exclusive creation of the
target. The server should check for the presence of a duplicate
object by name. If the object does not exist, the server creates the
object and stores the verifier with the object. If the object does
exist and the stored verifier matches the client provided verifier,
the server uses the existing object as the newly created object. If
the stored verifier does not match, then an error of NFS4ERR_EXIST is
returned. No attributes may be provided in this case, since the
server may use an attribute of the target object to store the
verifier. If the server uses an attribute to store the exclusive
create verifier, it will signify which attribute by setting the
appropriate bit in the attribute mask that is returned in the
results.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 struct, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the link creation.
Upon successful creation, the current filehandle is replaced by that
of the new object.
The OPEN operation provides for Windows share reservation capability
with the use of the share_access and share_deny fields of the OPEN
arguments. The client specifies at OPEN the required share_access
and share_deny modes. For clients that do not directly support
SHAREs (i.e., UNIX), the expected deny value is DENY_NONE. In the
case that there is a existing SHARE reservation that conflicts with
the OPEN request, the server returns the error NFS4ERR_SHARE_DENIED.
For a complete SHARE request, the client must provide values for the
owner and seqid fields for the OPEN argument. For additional
discussion of SHARE semantics see the section on 'Share
Reservations'.
In the case that the client is recovering state from a server
failure, the claim field of the OPEN argument is used to signify that
the request is meant to reclaim state previously held.
The "claim" field of the OPEN argument is used to specify the file to
be opened and the state information which the client claims to
possess. There are four basic claim types which cover the various
situations for an OPEN. They are as follows:
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CLAIM_NULL
For the client, this is a new OPEN
request and there is no previous state
associate with the file for the client.
CLAIM_PREVIOUS
The client is claiming basic OPEN state
for a file that was held previous to a
server reboot. Generally used when a
server is returning persistent
filehandles; the client may not have the
file name to reclaim the OPEN.
CLAIM_DELEGATE_CUR
The client is claiming a delegation for
OPEN as granted by the server.
Generally this is done as part of
recalling a delegation.
CLAIM_DELEGATE_PREV
The client is claiming a delegation
granted to a previous client instance;
used after the client reboots. The
server MAY support CLAIM_DELEGATE_PREV.
If it does support CLAIM_DELEGATE_PREV,
SETCLIENTID_CONFIRM MUST NOT remove the
client's delegation state, and the
server MUST support the DELEGPURGE
operation.
For OPEN requests whose claim type is other than CLAIM_PREVIOUS
(i.e., requests other than those devoted to reclaiming opens after a
server reboot) that reach the server during its grace or lease
expiration period, the server returns an error of NFS4ERR_GRACE.
For any OPEN request, the server may return an open delegation, which
allows further opens and closes to be handled locally on the client
as described in the section Open Delegation. Note that delegation is
up to the server to decide. The client should never assume that
delegation will or will not be granted in a particular instance. It
should always be prepared for either case. A partial exception is
the reclaim (CLAIM_PREVIOUS) case, in which a delegation type is
claimed. In this case, delegation will always be granted, although
the server may specify an immediate recall in the delegation
structure.
The rflags returned by a successful OPEN allow the server to return
information governing how the open file is to be handled.
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OPEN4_RESULT_CONFIRM indicates that the client MUST execute an
OPEN_CONFIRM operation before using the open file.
OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
behavior supports the complete set of Posix locking techniques. From
this the client can choose to manage file locking state in a way to
handle a mis-match of file locking management.
If the component is of zero length, NFS4ERR_INVAL will be returned.
The component is also subject to the normal UTF-8, character support,
and name checks. See the section "UTF-8 Related Errors" for further
discussion.
When an OPEN is done and the specified lockowner already has the
resulting filehandle open, the result is to "OR" together the new
share and deny status together with the existing status. In this
case, only a single CLOSE need be done, even though multiple OPENs
were completed. When such an OPEN is done, checking of share
reservations for the new OPEN proceeds normally, with no exception
for the existing OPEN held by the same lockowner.
If the underlying filesystem at the server is only accessible in a
read-only mode and the OPEN request has specified ACCESS_WRITE or
ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
only filesystem.
As with the CREATE operation, the server MUST derive the owner, owner
ACE, group, or group ACE if any of the four attributes are required
and supported by the server's filesystem. For an OPEN with the
EXCLUSIVE4 createmode, the server has no choice, since such OPEN
calls do not include the createattrs field. Conversely, if
createattrs is specified, and includes owner or group (or
corresponding ACEs) that the principal in the RPC call's credentials
does not have authorization to create files for, then the server may
return NFS4ERR_PERM.
In the case of a OPEN which specifies a size of zero (e.g.,
truncation) and the file has named attributes, the named attributes
are left as is. They are not removed.
IMPLEMENTATION
The OPEN operation contains support for EXCLUSIVE create. The
mechanism is similar to the support in NFS version 3 [RFC1813]. As
in NFS version 3, this mechanism provides reliable exclusive
creation. Exclusive create is invoked when the how parameter is
EXCLUSIVE. In this case, the client provides a verifier that can
reasonably be expected to be unique. A combination of a client
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identifier, perhaps the client network address, and a unique number
generated by the client, perhaps the RPC transaction identifier, may
be appropriate.
If the object does not exist, the server creates the object and
stores the verifier in stable storage. For filesystems that do not
provide a mechanism for the storage of arbitrary file attributes, the
server may use one or more elements of the object meta-data to store
the verifier. The verifier must be stored in stable storage to
prevent erroneous failure on retransmission of the request. It is
assumed that an exclusive create is being performed because exclusive
semantics are critical to the application. Because of the expected
usage, exclusive CREATE does not rely solely on the normally volatile
duplicate request cache for storage of the verifier. The duplicate
request cache in volatile storage does not survive a crash and may
actually flush on a long network partition, opening failure windows.
In the UNIX local filesystem environment, the expected storage
location for the verifier on creation is the meta-data (time stamps)
of the object. For this reason, an exclusive object create may not
include initial attributes because the server would have nowhere to
store the verifier.
If the server can not support these exclusive create semantics,
possibly because of the requirement to commit the verifier to stable
storage, it should fail the OPEN request with the error,
NFS4ERR_NOTSUPP.
During an exclusive CREATE request, if the object already exists, the
server reconstructs the object's verifier and compares it with the
verifier in the request. If they match, the server treats the request
as a success. The request is presumed to be a duplicate of an
earlier, successful request for which the reply was lost and that the
server duplicate request cache mechanism did not detect. If the
verifiers do not match, the request is rejected with the status,
NFS4ERR_EXIST.
Once the client has performed a successful exclusive create, it must
issue a SETATTR to set the correct object attributes. Until it does
so, it should not rely upon any of the object attributes, since the
server implementation may need to overload object meta-data to store
the verifier. The subsequent SETATTR must not occur in the same
COMPOUND request as the OPEN. This separation will guarantee that
the exclusive create mechanism will continue to function properly in
the face of retransmission of the request.
Use of the GUARDED attribute does not provide exactly-once semantics.
In particular, if a reply is lost and the server does not detect the
retransmission of the request, the operation can fail with
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NFS4ERR_EXIST, even though the create was performed successfully.
The client would use this behavior in the case that the application
has not requested an exclusive create but has asked to have the file
truncated when the file is opened. In the case of the client timing
out and retransmitting the create request, the client can use GUARDED
to prevent against a sequence like: create, write, create
(retransmitted) from occurring.
For SHARE reservations, the client must specify a value for
share_access that is one of READ, WRITE, or BOTH. For share_deny,
the client must specify one of NONE, READ, WRITE, or BOTH. If the
client fails to do this, the server must return NFS4ERR_INVAL.
Based on the share_access value (READ, WRITE, or BOTH) the client
should check that the requester has the proper access rights to
perform the specified operation. This would generally be the results
of applying the ACL access rules to the file for the current
requester. However, just as with the ACCESS operation, the client
should not attempt to second-guess the server's decisions, as access
rights may change and may be subject to server administrative
controls outside the ACL framework. If the requester is not
authorized to READ or WRITE (depending on the share_access value),
the server must return NFS4ERR_ACCESS. Note that since the NFS
version 4 protocol does not impose any requirement that READs and
WRITEs issued for an open file have the same credentials as the OPEN
itself, the server still must do appropriate access checking on the
READs and WRITEs themselves.
If the component provided to OPEN is a symbolic link, the error
NFS4ERR_SYMLINK will be returned to the client. If the current
filehandle is not a directory, the error NFS4ERR_NOTDIR will be
returned.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_ATTRNOTSUPP
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADOWNER
NFS4ERR_BAD_SEQID
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_EXPIRED
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NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_IO
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTSUPP
NFS4ERR_NO_GRACE
NFS4ERR_PERM
NFS4ERR_RECLAIM_BAD
NFS4ERR_RECLAIM_CONFLICT
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_SHARE_DENIED
NFS4ERR_STALE
NFS4ERR_STALE_CLIENTID
NFS4ERR_SYMLINK
NFS4ERR_WRONGSEC
SYNOPSIS
(cfh) createdir -> (cfh)
ARGUMENT
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
RESULT
struct OPENATTR4res {
/* CURRENT_FH: named attr directory*/
nfsstat4 status;
};
Shepler, et al. Standards Track [Page 178]
RFC 3530 NFS version 4 Protocol April 2003
DESCRIPTION
The OPENATTR operation is used to obtain the filehandle of the named
attribute directory associated with the current filehandle. The
result of the OPENATTR will be a filehandle to an object of type
NF4ATTRDIR. From this filehandle, READDIR and LOOKUP operations can
be used to obtain filehandles for the various named attributes
associated with the original filesystem object. Filehandles returned
within the named attribute directory will have a type of
NF4NAMEDATTR.
The createdir argument allows the client to signify if a named
attribute directory should be created as a result of the OPENATTR
operation. Some clients may use the OPENATTR operation with a value
of FALSE for createdir to determine if any named attributes exist for
the object. If none exist, then NFS4ERR_NOENT will be returned. If
createdir has a value of TRUE and no named attribute directory
exists, one is created. The creation of a named attribute directory
assumes that the server has implemented named attribute support in
this fashion and is not required to do so by this definition.
IMPLEMENTATION
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
client.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_FHEXPIRED
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
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SYNOPSIS
(cfh), seqid, stateid-> stateid
ARGUMENT
struct OPEN_CONFIRM4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
};
RESULT
struct OPEN_CONFIRM4resok {
stateid4 open_stateid;
};
union OPEN_CONFIRM4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_CONFIRM4resok resok4;
default:
void;
};
DESCRIPTION
This operation is used to confirm the sequence id usage for the first
time that a open_owner is used by a client. The stateid returned
from the OPEN operation is used as the argument for this operation
along with the next sequence id for the open_owner. The sequence id
passed to the OPEN_CONFIRM must be 1 (one) greater than the seqid
passed to the OPEN operation from which the open_confirm value was
obtained. If the server receives an unexpected sequence id with
respect to the original open, then the server assumes that the client
will not confirm the original OPEN and all state associated with the
original OPEN is released by the server.
On success, the current filehandle retains its value.
IMPLEMENTATION
A given client might generate many open_owner4 data structures for a
given clientid. The client will periodically either dispose of its
open_owner4s or stop using them for indefinite periods of time. The
latter situation is why the NFS version 4 protocol does not have an
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RFC 3530 NFS version 4 Protocol April 2003
explicit operation to exit an open_owner4: such an operation is of no
use in that situation. Instead, to avoid unbounded memory use, the
server needs to implement a strategy for disposing of open_owner4s
that have no current lock, open, or delegation state for any files
and have not been used recently. The time period used to determine
when to dispose of open_owner4s is an implementation choice. The
time period should certainly be no less than the lease time plus any
grace period the server wishes to implement beyond a lease time. The
OPEN_CONFIRM operation allows the server to safely dispose of unused
open_owner4 data structures.
In the case that a client issues an OPEN operation and the server no
longer has a record of the open_owner4, the server needs to ensure
that this is a new OPEN and not a replay or retransmission.
Servers must not require confirmation on OPENs that grant delegations
or are doing reclaim operations. See section "Use of Open
Confirmation" for details. The server can easily avoid this by
noting whether it has disposed of one open_owner4 for the given
clientid. If the server does not support delegation, it might simply
maintain a single bit that notes whether any open_owner4 (for any
client) has been disposed of.
The server must hold unconfirmed OPEN state until one of three events
occur. First, the client sends an OPEN_CONFIRM request with the
appropriate sequence id and stateid within the lease period. In this
case, the OPEN state on the server goes to confirmed, and the
open_owner4 on the server is fully established.
Second, the client sends another OPEN request with a sequence id that
is incorrect for the open_owner4 (out of sequence). In this case,
the server assumes the second OPEN request is valid and the first one
is a replay. The server cancels the OPEN state of the first OPEN
request, establishes an unconfirmed OPEN state for the second OPEN
request, and responds to the second OPEN request with an indication
that an OPEN_CONFIRM is needed. The process then repeats itself.
While there is a potential for a denial of service attack on the
client, it is mitigated if the client and server require the use of a
security flavor based on Kerberos V5, LIPKEY, or some other flavor
that uses cryptography.
What if the server is in the unconfirmed OPEN state for a given
open_owner4, and it receives an operation on the open_owner4 that has
a stateid but the operation is not OPEN, or it is OPEN_CONFIRM but
with the wrong stateid? Then, even if the seqid is correct, the
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server returns NFS4ERR_BAD_STATEID, because the server assumes the
operation is a replay: if the server has no established OPEN state,
then there is no way, for example, a LOCK operation could be valid.
Third, neither of the two aforementioned events occur for the
open_owner4 within the lease period. In this case, the OPEN state is
canceled and disposal of the open_owner4 can occur.
ERRORS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
SYNOPSIS
(cfh), stateid, seqid, access, deny -> stateid
ARGUMENT
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
RESULT
struct OPEN_DOWNGRADE4resok {
stateid4 open_stateid;
};
Shepler, et al. Standards Track [Page 182]
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union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
DESCRIPTION
This operation is used to adjust the share_access and share_deny bits
for a given open. This is necessary when a given openowner opens the
same file multiple times with different share_access and share_deny
flags. In this situation, a close of one of the opens may change the
appropriate share_access and share_deny flags to remove bits
associated with opens no longer in effect.
The share_access and share_deny bits specified in this operation
replace the current ones for the specified open file. The
share_access and share_deny bits specified must be exactly equal to
the union of the share_access and share_deny bits specified for some
subset of the OPENs in effect for current openowner on the current
file. If that constraint is not respected, the error NFS4ERR_INVAL
should be returned. Since share_access and share_deny bits are
subsets of those already granted, it is not possible for this request
to be denied because of conflicting share reservations.
On success, the current filehandle retains its value.
ERRORS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
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SYNOPSIS
filehandle -> (cfh)
ARGUMENT
struct PUTFH4args {
nfs_fh4 object;
};
RESULT
struct PUTFH4res {
/* CURRENT_FH: */
nfsstat4 status;
};
DESCRIPTION
Replaces the current filehandle with the filehandle provided as an
argument.
If the security mechanism used by the requester does not meet the
requirements of the filehandle provided to this operation, the server
MUST return NFS4ERR_WRONGSEC.
IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
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SYNOPSIS
- -> (cfh)
ARGUMENT
void;
RESULT
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
DESCRIPTION
Replaces the current filehandle with the filehandle that represents
the public filehandle of the server's name space. This filehandle
may be different from the "root" filehandle which may be associated
with some other directory on the server.
The public filehandle represents the concepts embodied in [RFC2054],
[RFC2055], [RFC2224]. The intent for NFS version 4 is that the
public filehandle (represented by the PUTPUBFH operation) be used as
a method of providing WebNFS server compatibility with NFS versions 2
and 3.
The public filehandle and the root filehandle (represented by the
PUTROOTFH operation) should be equivalent. If the public and root
filehandles are not equivalent, then the public filehandle MUST be a
descendant of the root filehandle.
IMPLEMENTATION
Used as the first operator in an NFS request to set the context for
following operations.
With the NFS version 2 and 3 public filehandle, the client is able to
specify whether the path name provided in the LOOKUP should be
evaluated as either an absolute path relative to the server's root or
relative to the public filehandle. [RFC2224] contains further
discussion of the functionality. With NFS version 4, that type of
specification is not directly available in the LOOKUP operation. The
reason for this is because the component separators needed to specify
absolute vs. relative are not allowed in NFS version 4. Therefore,
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the client is responsible for constructing its request such that the
use of either PUTROOTFH or PUTPUBFH are used to signify absolute or
relative evaluation of an NFS URL respectively.
Note that there are warnings mentioned in [RFC2224] with respect to
the use of absolute evaluation and the restrictions the server may
place on that evaluation with respect to how much of its namespace
has been made available. These same warnings apply to NFS version 4.
It is likely, therefore that because of server implementation
details, an NFS version 3 absolute public filehandle lookup may
behave differently than an NFS version 4 absolute resolution.
There is a form of security negotiation as described in [RFC2755]
that uses the public filehandle a method of employing SNEGO. This
method is not available with NFS version 4 as filehandles are not
overloaded with special meaning and therefore do not provide the same
framework as NFS versions 2 and 3. Clients should therefore use the
security negotiation mechanisms described in this RFC.
ERRORS
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_WRONGSEC
SYNOPSIS
- -> (cfh)
ARGUMENT
void;
RESULT
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
Shepler, et al. Standards Track [Page 186]
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DESCRIPTION
Replaces the current filehandle with the filehandle that represents
the root of the server's name space. From this filehandle a LOOKUP
operation can locate any other filehandle on the server. This
filehandle may be different from the "public" filehandle which may be
associated with some other directory on the server.
IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
ERRORS
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_WRONGSEC
SYNOPSIS
(cfh), stateid, offset, count -> eof, data
ARGUMENT
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
RESULT
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
Shepler, et al. Standards Track [Page 187]
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DESCRIPTION
The READ operation reads data from the regular file identified by the
current filehandle.
The client provides an offset of where the READ is to start and a
count of how many bytes are to be read. An offset of 0 (zero) means
to read data starting at the beginning of the file. If offset is
greater than or equal to the size of the file, the status, NFS4_OK,
is returned with a data length set to 0 (zero) and eof is set to
TRUE. The READ is subject to access permissions checking.
If the client specifies a count value of 0 (zero), the READ succeeds
and returns 0 (zero) bytes of data again subject to access
permissions checking. The server may choose to return fewer bytes
than specified by the client. The client needs to check for this
condition and handle the condition appropriately.
The stateid value for a READ request represents a value returned from
a previous record lock or share reservation request. The stateid is
used by the server to verify that the associated share reservation
and any record locks are still valid and to update lease timeouts for
the client.
If the read ended at the end-of-file (formally, in a correctly formed
READ request, if offset + count is equal to the size of the file), or
the read request extends beyond the size of the file (if offset +
count is greater than the size of the file), eof is returned as TRUE;
otherwise it is FALSE. A successful READ of an empty file will
always return eof as TRUE.
If the current filehandle is not a regular file, an error will be
returned to the client. In the case the current filehandle
represents a directory, NFS4ERR_ISDIR is return; otherwise,
NFS4ERR_INVAL is returned.
For a READ with a stateid value of all bits 0, the server MAY allow
the READ to be serviced subject to mandatory file locks or the
current share deny modes for the file. For a READ with a stateid
value of all bits 1, the server MAY allow READ operations to bypass
locking checks at the server.
On success, the current filehandle retains its value.
Shepler, et al. Standards Track [Page 188]
RFC 3530 NFS version 4 Protocol April 2003
IMPLEMENTATION
It is possible for the server to return fewer than count bytes of
data. If the server returns less than the count requested and eof is
set to FALSE, the client should issue another READ to get the
remaining data. A server may return less data than requested under
several circumstances. The file may have been truncated by another
client or perhaps on the server itself, changing the file size from
what the requesting client believes to be the case. This would
reduce the actual amount of data available to the client. It is
possible that the server may back off the transfer size and reduce
the read request return. Server resource exhaustion may also occur
necessitating a smaller read return.
If mandatory file locking is on for the file, and if the region
corresponding to the data to be read from file is write locked by an
owner not associated the stateid, the server will return the
NFS4ERR_LOCKED error. The client should try to get the appropriate
read record lock via the LOCK operation before re-attempting the
READ. When the READ completes, the client should release the record
lock via LOCKU.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_IO
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCKED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NXIO
NFS4ERR_OLD_STATEID
NFS4ERR_OPENMODE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
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SYNOPSIS
(cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
cookieverf { cookie, name, attrs }
ARGUMENT
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
RESULT
struct entry4 {
nfs_cookie4 cookie;
component4 name;
fattr4 attrs;
entry4 *nextentry;
};
struct dirlist4 {
entry4 *entries;
bool eof;
};
struct READDIR4resok {
verifier4 cookieverf;
dirlist4 reply;
};
union READDIR4res switch (nfsstat4 status) {
case NFS4_OK:
READDIR4resok resok4;
default:
void;
};
Shepler, et al. Standards Track [Page 190]
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DESCRIPTION
The READDIR operation retrieves a variable number of entries from a
filesystem directory and returns client requested attributes for each
entry along with information to allow the client to request
additional directory entries in a subsequent READDIR.
The arguments contain a cookie value that represents where the
READDIR should start within the directory. A value of 0 (zero) for
the cookie is used to start reading at the beginning of the
directory. For subsequent READDIR requests, the client specifies a
cookie value that is provided by the server on a previous READDIR
request.
The cookieverf value should be set to 0 (zero) when the cookie value
is 0 (zero) (first directory read). On subsequent requests, it
should be a cookieverf as returned by the server. The cookieverf
must match that returned by the READDIR in which the cookie was
acquired. If the server determines that the cookieverf is no longer
valid for the directory, the error NFS4ERR_NOT_SAME must be returned.
The dircount portion of the argument is a hint of the maximum number
of bytes of directory information that should be returned. This
value represents the length of the names of the directory entries and
the cookie value for these entries. This length represents the XDR
encoding of the data (names and cookies) and not the length in the
native format of the server.
The maxcount value of the argument is the maximum number of bytes for
the result. This maximum size represents all of the data being
returned within the READDIR4resok structure and includes the XDR
overhead. The server may return less data. If the server is unable
to return a single directory entry within the maxcount limit, the
error NFS4ERR_TOOSMALL will be returned to the client.
Finally, attr_request represents the list of attributes to be
returned for each directory entry supplied by the server.
On successful return, the server's response will provide a list of
directory entries. Each of these entries contains the name of the
directory entry, a cookie value for that entry, and the associated
attributes as requested. The "eof" flag has a value of TRUE if there
are no more entries in the directory.
The cookie value is only meaningful to the server and is used as a
"bookmark" for the directory entry. As mentioned, this cookie is
used by the client for subsequent READDIR operations so that it may
continue reading a directory. The cookie is similar in concept to a
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READ offset but should not be interpreted as such by the client.
Ideally, the cookie value should not change if the directory is
modified since the client may be caching these values.
In some cases, the server may encounter an error while obtaining the
attributes for a directory entry. Instead of returning an error for
the entire READDIR operation, the server can instead return the
attribute 'fattr4_rdattr_error'. With this, the server is able to
communicate the failure to the client and not fail the entire
operation in the instance of what might be a transient failure.
Obviously, the client must request the fattr4_rdattr_error attribute
for this method to work properly. If the client does not request the
attribute, the server has no choice but to return failure for the
entire READDIR operation.
For some filesystem environments, the directory entries "." and ".."
have special meaning and in other environments, they may not. If the
server supports these special entries within a directory, they should
not be returned to the client as part of the READDIR response. To
enable some client environments, the cookie values of 0, 1, and 2 are
to be considered reserved. Note that the UNIX client will use these
values when combining the server's response and local representations
to enable a fully formed UNIX directory presentation to the
application.
For READDIR arguments, cookie values of 1 and 2 should not be used
and for READDIR results cookie values of 0, 1, and 2 should not be
returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
The server's filesystem directory representations can differ greatly.
A client's programming interfaces may also be bound to the local
operating environment in a way that does not translate well into the
NFS protocol. Therefore the use of the dircount and maxcount fields
are provided to allow the client the ability to provide guidelines to
the server. If the client is aggressive about attribute collection
during a READDIR, the server has an idea of how to limit the encoded
response. The dircount field provides a hint on the number of
entries based solely on the names of the directory entries. Since it
is a hint, it may be possible that a dircount value is zero. In this
case, the server is free to ignore the dircount value and return
directory information based on the specified maxcount value.
Shepler, et al. Standards Track [Page 192]
RFC 3530 NFS version 4 Protocol April 2003
The cookieverf may be used by the server to help manage cookie values
that may become stale. It should be a rare occurrence that a server
is unable to continue properly reading a directory with the provided
cookie/cookieverf pair. The server should make every effort to avoid
this condition since the application at the client may not be able to
properly handle this type of failure.
The use of the cookieverf will also protect the client from using
READDIR cookie values that may be stale. For example, if the file
system has been migrated, the server may or may not be able to use
the same cookie values to service READDIR as the previous server
used. With the client providing the cookieverf, the server is able
to provide the appropriate response to the client. This prevents the
case where the server may accept a cookie value but the underlying
directory has changed and the response is invalid from the client's
context of its previous READDIR.
Since some servers will not be returning "." and ".." entries as has
been done with previous versions of the NFS protocol, the client that
requires these entries be present in READDIR responses must fabricate
them.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_COOKIE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_TOOSMALL
SYNOPSIS
(cfh) -> linktext
Shepler, et al. Standards Track [Page 193]
RFC 3530 NFS version 4 Protocol April 2003
ARGUMENT
/* CURRENT_FH: symlink */
void;
RESULT
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
DESCRIPTION
READLINK reads the data associated with a symbolic link. The data is
a UTF-8 string that is opaque to the server. That is, whether
created by an NFS client or created locally on the server, the data
in a symbolic link is not interpreted when created, but is simply
stored.
On success, the current filehandle retains its value.
IMPLEMENTATION
A symbolic link is nominally a pointer to another file. The data is
not necessarily interpreted by the server, just stored in the file.
It is possible for a client implementation to store a path name that
is not meaningful to the server operating system in a symbolic link.
A READLINK operation returns the data to the client for
interpretation. If different implementations want to share access to
symbolic links, then they must agree on the interpretation of the
data in the symbolic link.
The READLINK operation is only allowed on objects of type NF4LNK.
The server should return the error, NFS4ERR_INVAL, if the object is
not of type, NF4LNK.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
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NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), filename -> change_info
ARGUMENT
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
RESULT
struct REMOVE4resok {
change_info4 cinfo;
}
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
}
DESCRIPTION
The REMOVE operation removes (deletes) a directory entry named by
filename from the directory corresponding to the current filehandle.
If the entry in the directory was the last reference to the
corresponding filesystem object, the object may be destroyed.
Shepler, et al. Standards Track [Page 195]
RFC 3530 NFS version 4 Protocol April 2003
For the directory where the filename was removed, the server returns
change_info4 information in cinfo. With the atomic field of the
change_info4 struct, the server will indicate if the before and after
change attributes were obtained atomically with respect to the
removal.
If the target has a length of 0 (zero), or if target does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
NFS versions 2 and 3 required a different operator RMDIR for
directory removal and REMOVE for non-directory removal. This allowed
clients to skip checking the file type when being passed a non-
directory delete system call (e.g., unlink() in POSIX) to remove a
directory, as well as the converse (e.g., a rmdir() on a non-
directory) because they knew the server would check the file type.
NFS version 4 REMOVE can be used to delete any directory entry
independent of its file type. The implementor of an NFS version 4
client's entry points from the unlink() and rmdir() system calls
should first check the file type against the types the system call is
allowed to remove before issuing a REMOVE. Alternatively, the
implementor can produce a COMPOUND call that includes a LOOKUP/VERIFY
sequence to verify the file type before a REMOVE operation in the
same COMPOUND call.
The concept of last reference is server specific. However, if the
numlinks field in the previous attributes of the object had the value
1, the client should not rely on referring to the object via a
filehandle. Likewise, the client should not rely on the resources
(disk space, directory entry, and so on) formerly associated with the
object becoming immediately available. Thus, if a client needs to be
able to continue to access a file after using REMOVE to remove it,
the client should take steps to make sure that the file will still be
accessible. The usual mechanism used is to RENAME the file from its
old name to a new hidden name.
If the server finds that the file is still open when the REMOVE
arrives:
o The server SHOULD NOT delete the file's directory entry if the
file was opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH.
Shepler, et al. Standards Track [Page 196]
RFC 3530 NFS version 4 Protocol April 2003
o If the file was not opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
directory entry. However, until last CLOSE of the file, the
server MAY continue to allow access to the file via its
filehandle.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_FILE_OPEN
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_NOTEMPTY
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(sfh), oldname, (cfh), newname -> source_change_info,
target_change_info
ARGUMENT
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
Shepler, et al. Standards Track [Page 197]
RFC 3530 NFS version 4 Protocol April 2003
RESULT
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
DESCRIPTION
The RENAME operation renames the object identified by oldname in the
source directory corresponding to the saved filehandle, as set by the
SAVEFH operation, to newname in the target directory corresponding to
the current filehandle. The operation is required to be atomic to
the client. Source and target directories must reside on the same
filesystem on the server. On success, the current filehandle will
continue to be the target directory.
If the target directory already contains an entry with the name,
newname, the source object must be compatible with the target:
either both are non-directories or both are directories and the
target must be empty. If compatible, the existing target is removed
before the rename occurs (See the IMPLEMENTATION subsection of the
section "Operation 28: REMOVE - Remove Filesystem Object" for client
and server actions whenever a target is removed). If they are not
compatible or if the target is a directory but not empty, the server
will return the error, NFS4ERR_EXIST.
If oldname and newname both refer to the same file (they might be
hard links of each other), then RENAME should perform no action and
return success.
For both directories involved in the RENAME, the server returns
change_info4 information. With the atomic field of the change_info4
struct, the server will indicate if the before and after change
attributes were obtained atomically with respect to the rename.
If the oldname refers to a named attribute and the saved and current
filehandles refer to different filesystem objects, the server will
return NFS4ERR_XDEV just as if the saved and current filehandles
represented directories on different filesystems.
Shepler, et al. Standards Track [Page 198]
RFC 3530 NFS version 4 Protocol April 2003
If the oldname or newname has a length of 0 (zero), or if oldname or
newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
will be returned.
IMPLEMENTATION
The RENAME operation must be atomic to the client. The statement
"source and target directories must reside on the same filesystem on
the server" means that the fsid fields in the attributes for the
directories are the same. If they reside on different filesystems,
the error, NFS4ERR_XDEV, is returned.
Based on the value of the fh_expire_type attribute for the object,
the filehandle may or may not expire on a RENAME. However, server
implementors are strongly encouraged to attempt to keep filehandles
from expiring in this fashion.
On some servers, the file names "." and ".." are illegal as either
oldname or newname, and will result in the error NFS4ERR_BADNAME. In
addition, on many servers the case of oldname or newname being an
alias for the source directory will be checked for. Such servers
will return the error NFS4ERR_INVAL in these cases.
If either of the source or target filehandles are not directories,
the server will return NFS4ERR_NOTDIR.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_FILE_OPEN
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTEMPTY
NFS4ERR_RESOURCE
Shepler, et al. Standards Track [Page 199]
RFC 3530 NFS version 4 Protocol April 2003
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
NFS4ERR_XDEV
SYNOPSIS
clientid -> ()
ARGUMENT
struct RENEW4args {
clientid4 clientid;
};
RESULT
struct RENEW4res {
nfsstat4 status;
};
DESCRIPTION
The RENEW operation is used by the client to renew leases which it
currently holds at a server. In processing the RENEW request, the
server renews all leases associated with the client. The associated
leases are determined by the clientid provided via the SETCLIENTID
operation.
IMPLEMENTATION
When the client holds delegations, it needs to use RENEW to detect
when the server has determined that the callback path is down. When
the server has made such a determination, only the RENEW operation
will renew the lease on delegations. If the server determines the
callback path is down, it returns NFS4ERR_CB_PATH_DOWN. Even though
it returns NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
the record locks and share reservations that the client has
established on the server. If for some reason the lock and share
reservation lease cannot be renewed, then the server MUST return an
error other than NFS4ERR_CB_PATH_DOWN, even if the callback path is
also down.
Shepler, et al. Standards Track [Page 200]
RFC 3530 NFS version 4 Protocol April 2003
The client that issues RENEW MUST choose the principal, RPC security
flavor, and if applicable, GSS-API mechanism and service via one of
the following algorithms:
o The client uses the same principal, RPC security flavor -- and if
the flavor was RPCSEC_GSS -- the same mechanism and service that
was used when the client id was established via
SETCLIENTID_CONFIRM.
o The client uses any principal, RPC security flavor mechanism and
service combination that currently has an OPEN file on the server.
I.e., the same principal had a successful OPEN operation, the
file is still open by that principal, and the flavor, mechanism,
and service of RENEW match that of the previous OPEN.
The server MUST reject a RENEW that does not use one the
aforementioned algorithms, with the error NFS4ERR_ACCESS.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADXDR
NFS4ERR_CB_PATH_DOWN
NFS4ERR_EXPIRED
NFS4ERR_LEASE_MOVED
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
SYNOPSIS
(sfh) -> (cfh)
ARGUMENT
/* SAVED_FH: */
void;
RESULT
struct RESTOREFH4res {
/* CURRENT_FH: value of saved fh */
nfsstat4 status;
};
Shepler, et al. Standards Track [Page 201]
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DESCRIPTION
Set the current filehandle to the value in the saved filehandle. If
there is no saved filehandle then return the error NFS4ERR_RESTOREFH.
IMPLEMENTATION
Operations like OPEN and LOOKUP use the current filehandle to
represent a directory and replace it with a new filehandle. Assuming
the previous filehandle was saved with a SAVEFH operator, the
previous filehandle can be restored as the current filehandle. This
is commonly used to obtain post-operation attributes for the
directory, e.g.,
PUTFH (directory filehandle)
SAVEFH
GETATTR attrbits (pre-op dir attrs)
CREATE optbits "foo" attrs
GETATTR attrbits (file attributes)
RESTOREFH
GETATTR attrbits (post-op dir attrs)
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_RESOURCE
NFS4ERR_RESTOREFH
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
SYNOPSIS
(cfh) -> (sfh)
ARGUMENT
/* CURRENT_FH: */
void;
Shepler, et al. Standards Track [Page 202]
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RESULT
struct SAVEFH4res {
/* SAVED_FH: value of current fh */
nfsstat4 status;
};
DESCRIPTION
Save the current filehandle. If a previous filehandle was saved then
it is no longer accessible. The saved filehandle can be restored as
the current filehandle with the RESTOREFH operator.
On success, the current filehandle retains its value.
IMPLEMENTATION
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), name -> { secinfo }
ARGUMENT
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
RESULT
enum rpc_gss_svc_t {/* From RFC 2203 */
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
Shepler, et al. Standards Track [Page 203]
RFC 3530 NFS version 4 Protocol April 2003
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
union secinfo4 switch (uint32_t flavor) {
case RPCSEC_GSS:
rpcsec_gss_info flavor_info;
default:
void;
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
SECINFO4resok resok4;
default:
void;
};
DESCRIPTION
The SECINFO operation is used by the client to obtain a list of valid
RPC authentication flavors for a specific directory filehandle, file
name pair. SECINFO should apply the same access methodology used for
LOOKUP when evaluating the name. Therefore, if the requester does
not have the appropriate access to LOOKUP the name then SECINFO must
behave the same way and return NFS4ERR_ACCESS.
The result will contain an array which represents the security
mechanisms available, with an order corresponding to server's
preferences, the most preferred being first in the array. The client
is free to pick whatever security mechanism it both desires and
supports, or to pick in the server's preference order the first one
it supports. The array entries are represented by the secinfo4
structure. The field 'flavor' will contain a value of AUTH_NONE,
AUTH_SYS (as defined in [RFC1831]), or RPCSEC_GSS (as defined in
[RFC2203]).
For the flavors AUTH_NONE and AUTH_SYS, no additional security
information is returned. For a return value of RPCSEC_GSS, a
security triple is returned that contains the mechanism object id (as
defined in [RFC2743]), the quality of protection (as defined in
[RFC2743]) and the service type (as defined in [RFC2203]). It is
possible for SECINFO to return multiple entries with flavor equal to
RPCSEC_GSS with different security triple values.
Shepler, et al. Standards Track [Page 204]
RFC 3530 NFS version 4 Protocol April 2003
On success, the current filehandle retains its value.
If the name has a length of 0 (zero), or if name does not obey the
UTF-8 definition, the error NFS4ERR_INVAL will be returned.
IMPLEMENTATION
The SECINFO operation is expected to be used by the NFS client when
the error value of NFS4ERR_WRONGSEC is returned from another NFS
operation. This signifies to the client that the server's security
policy is different from what the client is currently using. At this
point, the client is expected to obtain a list of possible security
flavors and choose what best suits its policies.
As mentioned, the server's security policies will determine when a
client request receives NFS4ERR_WRONGSEC. The operations which may
receive this error are: LINK, LOOKUP, OPEN, PUTFH, PUTPUBFH,
PUTROOTFH, RESTOREFH, RENAME, and indirectly READDIR. LINK and
RENAME will only receive this error if the security used for the
operation is inappropriate for saved filehandle. With the exception
of READDIR, these operations represent the point at which the client
can instantiate a filehandle into the "current filehandle" at the
server. The filehandle is either provided by the client (PUTFH,
PUTPUBFH, PUTROOTFH) or generated as a result of a name to filehandle
translation (LOOKUP and OPEN). RESTOREFH is different because the
filehandle is a result of a previous SAVEFH. Even though the
filehandle, for RESTOREFH, might have previously passed the server's
inspection for a security match, the server will check it again on
RESTOREFH to ensure that the security policy has not changed.
If the client wants to resolve an error return of NFS4ERR_WRONGSEC,
the following will occur:
o For LOOKUP and OPEN, the client will use SECINFO with the same
current filehandle and name as provided in the original LOOKUP or
OPEN to enumerate the available security triples.
o For LINK, PUTFH, RENAME, and RESTOREFH, the client will use
SECINFO and provide the parent directory filehandle and object
name which corresponds to the filehandle originally provided by
the PUTFH RESTOREFH, or for LINK and RENAME, the SAVEFH.
o For PUTROOTFH and PUTPUBFH, the client will be unable to use the
SECINFO operation since SECINFO requires a current filehandle and
none exist for these two operations. Therefore, the client must
iterate through the security triples available at the client and
reattempt the PUTROOTFH or PUTPUBFH operation. In the unfortunate
event none of the MANDATORY security triples are supported by the
Shepler, et al. Standards Track [Page 205]
RFC 3530 NFS version 4 Protocol April 2003
client and server, the client SHOULD try using others that support
integrity. Failing that, the client can try using AUTH_NONE, but
because such forms lack integrity checks, this puts the client at
risk. Nonetheless, the server SHOULD allow the client to use
whatever security form the client requests and the server
supports, since the risks of doing so are on the client.
The READDIR operation will not directly return the NFS4ERR_WRONGSEC
error. However, if the READDIR request included a request for
attributes, it is possible that the READDIR request's security triple
does not match that of a directory entry. If this is the case and
the client has requested the rdattr_error attribute, the server will
return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
See the section "Security Considerations" for a discussion on the
recommendations for security flavor used by SECINFO.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADNAME
NFS4ERR_BADXDR
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), stateid, attrmask, attr_vals -> attrsset
ARGUMENT
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
Shepler, et al. Standards Track [Page 206]
RFC 3530 NFS version 4 Protocol April 2003
RESULT
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
DESCRIPTION
The SETATTR operation changes one or more of the attributes of a
filesystem object. The new attributes are specified with a bitmap
and the attributes that follow the bitmap in bit order.
The stateid argument for SETATTR is used to provide file locking
context that is necessary for SETATTR requests that set the size
attribute. Since setting the size attribute modifies the file's
data, it has the same locking requirements as a corresponding WRITE.
Any SETATTR that sets the size attribute is incompatible with a share
reservation that specifies DENY_WRITE. The area between the old
end-of-file and the new end-of-file is considered to be modified just
as would have been the case had the area in question been specified
as the target of WRITE, for the purpose of checking conflicts with
record locks, for those cases in which a server is implementing
mandatory record locking behavior. A valid stateid should always be
specified. When the file size attribute is not set, the special
stateid consisting of all bits zero should be passed.
On either success or failure of the operation, the server will return
the attrsset bitmask to represent what (if any) attributes were
successfully set. The attrsset in the response is a subset of the
bitmap4 that is part of the obj_attributes in the argument.
On success, the current filehandle retains its value.
IMPLEMENTATION
If the request specifies the owner attribute to be set, the server
should allow the operation to succeed if the current owner of the
object matches the value specified in the request. Some servers may
be implemented in a way as to prohibit the setting of the owner
attribute unless the requester has privilege to do so. If the server
is lenient in this one case of matching owner values, the client
implementation may be simplified in cases of creation of an object
followed by a SETATTR.
The file size attribute is used to request changes to the size of a
file. A value of 0 (zero) causes the file to be truncated, a value
less than the current size of the file causes data from new size to
Shepler, et al. Standards Track [Page 207]
RFC 3530 NFS version 4 Protocol April 2003
the end of the file to be discarded, and a size greater than the
current size of the file causes logically zeroed data bytes to be
added to the end of the file. Servers are free to implement this
using holes or actual zero data bytes. Clients should not make any
assumptions regarding a server's implementation of this feature,
beyond that the bytes returned will be zeroed. Servers must support
extending the file size via SETATTR.
SETATTR is not guaranteed atomic. A failed SETATTR may partially
change a file's attributes.
Changing the size of a file with SETATTR indirectly changes the
time_modify. A client must account for this as size changes can
result in data deletion.
The attributes time_access_set and time_modify_set are write-only
attributes constructed as a switched union so the client can direct
the server in setting the time values. If the switched union
specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
be used for the operation. If the switch union does not specify
SET_TO_CLIENT_TIME4, the server is to use its current time for the
SETATTR operation.
If server and client times differ, programs that compare client time
to file times can break. A time maintenance protocol should be used
to limit client/server time skew.
Use of a COMPOUND containing a VERIFY operation specifying only the
change attribute, immediately followed by a SETATTR, provides a means
whereby a client may specify a request that emulates the
functionality of the SETATTR guard mechanism of NFS version 3. Since
the function of the guard mechanism is to avoid changes to the file
attributes based on stale information, delays between checking of the
guard condition and the setting of the attributes have the potential
to compromise this function, as would the corresponding delay in the
NFS version 4 emulation. Therefore, NFS version 4 servers should
take care to avoid such delays, to the degree possible, when
executing such a request.
If the server does not support an attribute as requested by the
client, the server should return NFS4ERR_ATTRNOTSUPP.
A mask of the attributes actually set is returned by SETATTR in all
cases. That mask must not include attributes bits not requested to
be set by the client, and must be equal to the mask of attributes
requested to be set only if the SETATTR completes without error.
Shepler, et al. Standards Track [Page 208]
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ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_ATTRNOTSUPP
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADOWNER
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXPIRED
NFS4ERR_FBIG
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_LOCKED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_OLD_STATEID
NFS4ERR_OPENMODE
NFS4ERR_PERM
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
SYNOPSIS
client, callback, callback_ident -> clientid, setclientid_confirm
ARGUMENT
struct SETCLIENTID4args {
nfs_client_id4 client;
cb_client4 callback;
uint32_t callback_ident;
};
Shepler, et al. Standards Track [Page 209]
RFC 3530 NFS version 4 Protocol April 2003
RESULT
struct SETCLIENTID4resok {
clientid4 clientid;
verifier4 setclientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
clientaddr4 client_using;
default:
void;
};
DESCRIPTION
The client uses the SETCLIENTID operation to notify the server of its
intention to use a particular client identifier, callback, and
callback_ident for subsequent requests that entail creating lock,
share reservation, and delegation state on the server. Upon
successful completion the server will return a shorthand clientid
which, if confirmed via a separate step, will be used in subsequent
file locking and file open requests. Confirmation of the clientid
must be done via the SETCLIENTID_CONFIRM operation to return the
clientid and setclientid_confirm values, as verifiers, to the server.
The reason why two verifiers are necessary is that it is possible to
use SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
callback_ident information but not the shorthand clientid. In that
event, the setclientid_confirm value is effectively the only
verifier.
The callback information provided in this operation will be used if
the client is provided an open delegation at a future point.
Therefore, the client must correctly reflect the program and port
numbers for the callback program at the time SETCLIENTID is used.
The callback_ident value is used by the server on the callback. The
client can leverage the callback_ident to eliminate the need for more
than one callback RPC program number, while still being able to
determine which server is initiating the callback.
Shepler, et al. Standards Track [Page 210]
RFC 3530 NFS version 4 Protocol April 2003
IMPLEMENTATION
To understand how to implement SETCLIENTID, make the following
notations. Let:
x be the value of the client.id subfield of the SETCLIENTID4args
structure.
v be the value of the client.verifier subfield of the
SETCLIENTID4args structure.
c be the value of the clientid field returned in the
SETCLIENTID4resok structure.
k represent the value combination of the fields callback and
callback_ident fields of the SETCLIENTID4args structure.
s be the setclientid_confirm value returned in the
SETCLIENTID4resok structure.
{ v, x, c, k, s }
be a quintuple for a client record. A client record is
confirmed if there has been a SETCLIENTID_CONFIRM operation to
confirm it. Otherwise it is unconfirmed. An unconfirmed
record is established by a SETCLIENTID call.
Since SETCLIENTID is a non-idempotent operation, let us assume that
the server is implementing the duplicate request cache (DRC).
When the server gets a SETCLIENTID { v, x, k } request, it processes
it in the following manner.
o It first looks up the request in the DRC. If there is a hit, it
returns the result cached in the DRC. The server does NOT remove
client state (locks, shares, delegations) nor does it modify any
recorded callback and callback_ident information for client { x }.
For any DRC miss, the server takes the client id string x, and
searches for client records for x that the server may have
recorded from previous SETCLIENTID calls. For any confirmed record
with the same id string x, if the recorded principal does not
match that of SETCLIENTID call, then the server returns a
NFS4ERR_CLID_INUSE error.
For brevity of discussion, the remaining description of the
processing assumes that there was a DRC miss, and that where the
server has previously recorded a confirmed record for client x,
the aforementioned principal check has successfully passed.
Shepler, et al. Standards Track [Page 211]
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o The server checks if it has recorded a confirmed record for { v,
x, c, l, s }, where l may or may not equal k. If so, and since the
id verifier v of the request matches that which is confirmed and
recorded, the server treats this as a probable callback
information update and records an unconfirmed { v, x, c, k, t }
and leaves the confirmed { v, x, c, l, s } in place, such that t
!= s. It does not matter if k equals l or not. Any pre-existing
unconfirmed { v, x, c, *, * } is removed.
The server returns { c, t }. It is indeed returning the old
clientid4 value c, because the client apparently only wants to
update callback value k to value l. It's possible this request is
one from the Byzantine router that has stale callback information,
but this is not a problem. The callback information update is
only confirmed if followed up by a SETCLIENTID_CONFIRM { c, t }.
The server awaits confirmation of k via
SETCLIENTID_CONFIRM { c, t }.
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has previously recorded a confirmed { u, x, c, l, s }
record such that v != u, l may or may not equal k, and has not
recorded any unconfirmed { *, x, *, *, * } record for x. The
server records an unconfirmed { v, x, d, k, t } (d != c, t != s).
The server returns { d, t }.
The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
{ d, t }.
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has previously recorded a confirmed { u, x, c, l, s }
record such that v != u, l may or may not equal k, and recorded an
unconfirmed { w, x, d, m, t } record such that c != d, t != s, m
may or may not equal k, m may or may not equal l, and k may or may
not equal l. Whether w == v or w != v makes no difference. The
server simply removes the unconfirmed { w, x, d, m, t } record and
replaces it with an unconfirmed { v, x, e, k, r } record, such
that e != d, e != c, r != t, r != s.
The server returns { e, r }.
The server awaits confirmation of { e, k } via
SETCLIENTID_CONFIRM { e, r }.
Shepler, et al. Standards Track [Page 212]
RFC 3530 NFS version 4 Protocol April 2003
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has no confirmed { *, x, *, *, * } for x. It may or may
not have recorded an unconfirmed { u, x, c, l, s }, where l may or
may not equal k, and u may or may not equal v. Any unconfirmed
record { u, x, c, l, * }, regardless whether u == v or l == k, is
replaced with an unconfirmed record { v, x, d, k, t } where d !=
c, t != s.
The server returns { d, t }.
The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
{ d, t }. The server does NOT remove client
(lock/share/delegation) state for x.
The server generates the clientid and setclientid_confirm values and
must take care to ensure that these values are extremely unlikely to
ever be regenerated.
ERRORS
NFS4ERR_BADXDR
NFS4ERR_CLID_INUSE
NFS4ERR_INVAL
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
SYNOPSIS
clientid, verifier -> -
ARGUMENT
struct SETCLIENTID_CONFIRM4args {
clientid4 clientid;
verifier4 setclientid_confirm;
};
RESULT
struct SETCLIENTID_CONFIRM4res {
nfsstat4 status;
};
Shepler, et al. Standards Track [Page 213]
RFC 3530 NFS version 4 Protocol April 2003
DESCRIPTION
This operation is used by the client to confirm the results from a
previous call to SETCLIENTID. The client provides the server
supplied (from a SETCLIENTID response) clientid. The server responds
with a simple status of success or failure.
IMPLEMENTATION
The client must use the SETCLIENTID_CONFIRM operation to confirm the
following two distinct cases:
o The client's use of a new shorthand client identifier (as returned
from the server in the response to SETCLIENTID), a new callback
value (as specified in the arguments to SETCLIENTID) and a new
callback_ident (as specified in the arguments to SETCLIENTID)
value. The client's use of SETCLIENTID_CONFIRM in this case also
confirms the removal of any of the client's previous relevant
leased state. Relevant leased client state includes record locks,
share reservations, and where the server does not support the
CLAIM_DELEGATE_PREV claim type, delegations. If the server
supports CLAIM_DELEGATE_PREV, then SETCLIENTID_CONFIRM MUST NOT
remove delegations for this client; relevant leased client state
would then just include record locks and share reservations.
o The client's re-use of an old, previously confirmed, shorthand
client identifier, a new callback value, and a new callback_ident
value. The client's use of SETCLIENTID_CONFIRM in this case MUST
NOT result in the removal of any previous leased state (locks,
share reservations, and delegations)
We use the same notation and definitions for v, x, c, k, s, and
unconfirmed and confirmed client records as introduced in the
description of the SETCLIENTID operation. The arguments to
SETCLIENTID_CONFIRM are indicated by the notation { c, s }, where c
is a value of type clientid4, and s is a value of type verifier4
corresponding to the setclientid_confirm field.
As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
operation, and we assume that the server is implementing the
duplicate request cache (DRC).
When the server gets a SETCLIENTID_CONFIRM { c, s } request, it
processes it in the following manner.
Shepler, et al. Standards Track [Page 214]
RFC 3530 NFS version 4 Protocol April 2003
o It first looks up the request in the DRC. If there is a hit, it
returns the result cached in the DRC. The server does not remove
any relevant leased client state nor does it modify any recorded
callback and callback_ident information for client { x } as
represented by the shorthand value c.
For a DRC miss, the server checks for client records that match the
shorthand value c. The processing cases are as follows:
o The server has recorded an unconfirmed { v, x, c, k, s } record
and a confirmed { v, x, c, l, t } record, such that s != t. If
the principals of the records do not match that of the
SETCLIENTID_CONFIRM, the server returns NFS4ERR_CLID_INUSE, and no
relevant leased client state is removed and no recorded callback
and callback_ident information for client { x } is changed.
Otherwise, the confirmed { v, x, c, l, t } record is removed and
the unconfirmed { v, x, c, k, s } is marked as confirmed, thereby
modifying recorded and confirmed callback and callback_ident
information for client { x }.
The server does not remove any relevant leased client state.
The server returns NFS4_OK.
o The server has not recorded an unconfirmed { v, x, c, *, * } and
has recorded a confirmed { v, x, c, *, s }. If the principals of
the record and of SETCLIENTID_CONFIRM do not match, the server
returns NFS4ERR_CLID_INUSE without removing any relevant leased
client state and without changing recorded callback and
callback_ident values for client { x }.
If the principals match, then what has likely happened is that the
client never got the response from the SETCLIENTID_CONFIRM, and
the DRC entry has been purged. Whatever the scenario, since the
principals match, as well as { c, s } matching a confirmed record,
the server leaves client x's relevant leased client state intact,
leaves its callback and callback_ident values unmodified, and
returns NFS4_OK.
o The server has not recorded a confirmed { *, *, c, *, * }, and has
recorded an unconfirmed { *, x, c, k, s }. Even if this is a
retry from client, nonetheless the client's first
SETCLIENTID_CONFIRM attempt was not received by the server. Retry
or not, the server doesn't know, but it processes it as if were a
first try. If the principal of the unconfirmed { *, x, c, k, s }
record mismatches that of the SETCLIENTID_CONFIRM request the
server returns NFS4ERR_CLID_INUSE without removing any relevant
leased client state.
Shepler, et al. Standards Track [Page 215]
RFC 3530 NFS version 4 Protocol April 2003
Otherwise, the server records a confirmed { *, x, c, k, s }. If
there is also a confirmed { *, x, d, *, t }, the server MUST
remove the client x's relevant leased client state, and overwrite
the callback state with k. The confirmed record { *, x, d, *, t }
is removed.
Server returns NFS4_OK.
o The server has no record of a confirmed or unconfirmed { *, *, c,
*, s }. The server returns NFS4ERR_STALE_CLIENTID. The server
does not remove any relevant leased client state, nor does it
modify any recorded callback and callback_ident information for
any client.
The server needs to cache unconfirmed { v, x, c, k, s } client
records and await for some time their confirmation. As should be
clear from the record processing discussions for SETCLIENTID and
SETCLIENTID_CONFIRM, there are cases where the server does not
deterministically remove unconfirmed client records. To avoid
running out of resources, the server is not required to hold
unconfirmed records indefinitely. One strategy the server might use
is to set a limit on how many unconfirmed client records it will
maintain, and then when the limit would be exceeded, remove the
oldest record. Another strategy might be to remove an unconfirmed
record when some amount of time has elapsed. The choice of the amount
of time is fairly arbitrary but it is surely no higher than the
server's lease time period. Consider that leases need to be renewed
before the lease time expires via an operation from the client. If
the client cannot issue a SETCLIENTID_CONFIRM after a SETCLIENTID
before a period of time equal to that of a lease expires, then the
client is unlikely to be able maintain state on the server during
steady state operation.
If the client does send a SETCLIENTID_CONFIRM for an unconfirmed
record that the server has already deleted, the client will get
NFS4ERR_STALE_CLIENTID back. If so, the client should then start
over, and send SETCLIENTID to reestablish an unconfirmed client
record and get back an unconfirmed clientid and setclientid_confirm
verifier. The client should then send the SETCLIENTID_CONFIRM to
confirm the clientid.
SETCLIENTID_CONFIRM does not establish or renew a lease. However, if
SETCLIENTID_CONFIRM removes relevant leased client state, and that
state does not include existing delegations, the server MUST allow
the client a period of time no less than the value of lease_time
attribute, to reclaim, (via the CLAIM_DELEGATE_PREV claim type of the
OPEN operation) its delegations before removing unreclaimed
delegations.
Shepler, et al. Standards Track [Page 216]
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ERRORS
NFS4ERR_BADXDR
NFS4ERR_CLID_INUSE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
SYNOPSIS
(cfh), fattr -> -
ARGUMENT
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
RESULT
struct VERIFY4res {
nfsstat4 status;
};
DESCRIPTION
The VERIFY operation is used to verify that attributes have a value
assumed by the client before proceeding with following operations in
the compound request. If any of the attributes do not match then the
error NFS4ERR_NOT_SAME must be returned. The current filehandle
retains its value after successful completion of the operation.
IMPLEMENTATION
One possible use of the VERIFY operation is the following compound
sequence. With this the client is attempting to verify that the file
being removed will match what the client expects to be removed. This
sequence can help prevent the unintended deletion of a file.
PUTFH (directory filehandle)
LOOKUP (file name)
VERIFY (filehandle == fh)
PUTFH (directory filehandle)
REMOVE (file name)
Shepler, et al. Standards Track [Page 217]
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This sequence does not prevent a second client from removing and
creating a new file in the middle of this sequence but it does help
avoid the unintended result.
In the case that a recommended attribute is specified in the VERIFY
operation and the server does not support that attribute for the
filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
client.
When the attribute rdattr_error or any write-only attribute (e.g.,
time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
the client.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ATTRNOTSUPP
NFS4ERR_BADCHAR
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOT_SAME
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
SYNOPSIS
(cfh), stateid, offset, stable, data -> count, committed, writeverf
ARGUMENT
enum stable_how4 {
UNSTABLE4 = 0,
DATA_SYNC4 = 1,
FILE_SYNC4 = 2
};
struct WRITE4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
Shepler, et al. Standards Track [Page 218]
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stable_how4 stable;
opaque data<>;
};
RESULT
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
DESCRIPTION
The WRITE operation is used to write data to a regular file. The
target file is specified by the current filehandle. The offset
specifies the offset where the data should be written. An offset of
0 (zero) specifies that the write should start at the beginning of
the file. The count, as encoded as part of the opaque data
parameter, represents the number of bytes of data that are to be
written. If the count is 0 (zero), the WRITE will succeed and return
a count of 0 (zero) subject to permissions checking. The server may
choose to write fewer bytes than requested by the client.
Part of the write request is a specification of how the write is to
be performed. The client specifies with the stable parameter the
method of how the data is to be processed by the server. If stable
is FILE_SYNC4, the server must commit the data written plus all
filesystem metadata to stable storage before returning results. This
corresponds to the NFS version 2 protocol semantics. Any other
behavior constitutes a protocol violation. If stable is DATA_SYNC4,
then the server must commit all of the data to stable storage and
enough of the metadata to retrieve the data before returning. The
server implementor is free to implement DATA_SYNC4 in the same
fashion as FILE_SYNC4, but with a possible performance drop. If
stable is UNSTABLE4, the server is free to commit any part of the
data and the metadata to stable storage, including all or none,
before returning a reply to the client. There is no guarantee whether
or when any uncommitted data will subsequently be committed to stable
storage. The only guarantees made by the server are that it will not
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destroy any data without changing the value of verf and that it will
not commit the data and metadata at a level less than that requested
by the client.
The stateid value for a WRITE request represents a value returned
from a previous record lock or share reservation request. The
stateid is used by the server to verify that the associated share
reservation and any record locks are still valid and to update lease
timeouts for the client.
Upon successful completion, the following results are returned. The
count result is the number of bytes of data written to the file. The
server may write fewer bytes than requested. If so, the actual number
of bytes written starting at location, offset, is returned.
The server also returns an indication of the level of commitment of
the data and metadata via committed. If the server committed all data
and metadata to stable storage, committed should be set to
FILE_SYNC4. If the level of commitment was at least as strong as
DATA_SYNC4, then committed should be set to DATA_SYNC4. Otherwise,
committed must be returned as UNSTABLE4. If stable was FILE4_SYNC,
then committed must also be FILE_SYNC4: anything else constitutes a
protocol violation. If stable was DATA_SYNC4, then committed may be
FILE_SYNC4 or DATA_SYNC4: anything else constitutes a protocol
violation. If stable was UNSTABLE4, then committed may be either
FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.
The final portion of the result is the write verifier. The write
verifier is a cookie that the client can use to determine whether the
server has changed instance (boot) state between a call to WRITE and
a subsequent call to either WRITE or COMMIT. This cookie must be
consistent during a single instance of the NFS version 4 protocol
service and must be unique between instances of the NFS version 4
protocol server, where uncommitted data may be lost.
If a client writes data to the server with the stable argument set to
UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
UNSTABLE4, the client will follow up some time in the future with a
COMMIT operation to synchronize outstanding asynchronous data and
metadata with the server's stable storage, barring client error. It
is possible that due to client crash or other error that a subsequent
COMMIT will not be received by the server.
For a WRITE with a stateid value of all bits 0, the server MAY allow
the WRITE to be serviced subject to mandatory file locks or the
current share deny modes for the file. For a WRITE with a stateid
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value of all bits 1, the server MUST NOT allow the WRITE operation to
bypass locking checks at the server and are treated exactly the same
as if a stateid of all bits 0 were used.
On success, the current filehandle retains its value.
IMPLEMENTATION
It is possible for the server to write fewer bytes of data than
requested by the client. In this case, the server should not return
an error unless no data was written at all. If the server writes
less than the number of bytes specified, the client should issue
another WRITE to write the remaining data.
It is assumed that the act of writing data to a file will cause the
time_modified of the file to be updated. However, the time_modified
of the file should not be changed unless the contents of the file are
changed. Thus, a WRITE request with count set to 0 should not cause
the time_modified of the file to be updated.
The definition of stable storage has been historically a point of
contention. The following expected properties of stable storage may
help in resolving design issues in the implementation. Stable storage
is persistent storage that survives:
1. Repeated power failures.
2. Hardware failures (of any board, power supply, etc.).
3. Repeated software crashes, including reboot cycle.
This definition does not address failure of the stable storage module
itself.
The verifier is defined to allow a client to detect different
instances of an NFS version 4 protocol server over which cached,
uncommitted data may be lost. In the most likely case, the verifier
allows the client to detect server reboots. This information is
required so that the client can safely determine whether the server
could have lost cached data. If the server fails unexpectedly and
the client has uncommitted data from previous WRITE requests (done
with the stable argument set to UNSTABLE4 and in which the result
committed was returned as UNSTABLE4 as well) it may not have flushed
cached data to stable storage. The burden of recovery is on the
client and the client will need to retransmit the data to the server.
A suggested verifier would be to use the time that the server was
booted or the time the server was last started (if restarting the
server without a reboot results in lost buffers).
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The committed field in the results allows the client to do more
effective caching. If the server is committing all WRITE requests to
stable storage, then it should return with committed set to
FILE_SYNC4, regardless of the value of the stable field in the
arguments. A server that uses an NVRAM accelerator may choose to
implement this policy. The client can use this to increase the
effectiveness of the cache by discarding cached data that has already
been committed on the server.
Some implementations may return NFS4ERR_NOSPC instead of
NFS4ERR_DQUOT when a user's quota is exceeded. In the case that the
current filehandle is a directory, the server will return
NFS4ERR_ISDIR. If the current filehandle is not a regular file or a
directory, the server will return NFS4ERR_INVAL.
If mandatory file locking is on for the file, and corresponding
record of the data to be written file is read or write locked by an
owner that is not associated with the stateid, the server will return
NFS4ERR_LOCKED. If so, the client must check if the owner
corresponding to the stateid used with the WRITE operation has a
conflicting read lock that overlaps with the region that was to be
written. If the stateid's owner has no conflicting read lock, then
the client should try to get the appropriate write record lock via
the LOCK operation before re-attempting the WRITE. When the WRITE
completes, the client should release the record lock via LOCKU.
If the stateid's owner had a conflicting read lock, then the client
has no choice but to return an error to the application that
attempted the WRITE. The reason is that since the stateid's owner had
a read lock, the server either attempted to temporarily effectively
upgrade this read lock to a write lock, or the server has no upgrade
capability. If the server attempted to upgrade the read lock and
failed, it is pointless for the client to re-attempt the upgrade via
the LOCK operation, because there might be another client also trying
to upgrade. If two clients are blocked trying upgrade the same lock,
the clients deadlock. If the server has no upgrade capability, then
it is pointless to try a LOCK operation to upgrade.
ERRORS
NFS4ERR_ACCESS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXPIRED
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NFS4ERR_FBIG
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCKED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NXIO
NFS4ERR_OLD_STATEID
NFS4ERR_OPENMODE
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
SYNOPSIS
lockowner -> ()
ARGUMENT
struct RELEASE_LOCKOWNER4args {
lock_owner4 lock_owner;
};
RESULT
struct RELEASE_LOCKOWNER4res {
nfsstat4 status;
};
DESCRIPTION
This operation is used to notify the server that the lock_owner is no
longer in use by the client. This allows the server to release
cached state related to the specified lock_owner. If file locks,
associated with the lock_owner, are held at the server, the error
NFS4ERR_LOCKS_HELD will be returned and no further action will be
taken.
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RFC 3530 NFS version 4 Protocol April 2003
IMPLEMENTATION
The client may choose to use this operation to ease the amount of
server state that is held. Depending on behavior of applications at
the client, it may be important for the client to use this operation
since the server has certain obligations with respect to holding a
reference to a lock_owner as long as the associated file is open.
Therefore, if the client knows for certain that the lock_owner will
no longer be used under the context of the associated open_owner4, it
should use RELEASE_LOCKOWNER.
ERRORS
NFS4ERR_ADMIN_REVOKED
NFS4ERR_BADXDR
NFS4ERR_EXPIRED
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCKS_HELD
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
SYNOPSIS
<null> -> ()
ARGUMENT
void;
RESULT
struct ILLEGAL4res {
nfsstat4 status;
};
DESCRIPTION
This operation is a placeholder for encoding a result to handle the
case of the client sending an operation code within COMPOUND that is
not supported. See the COMPOUND procedure description for more
details.
The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
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RFC 3530 NFS version 4 Protocol April 2003
IMPLEMENTATION
A client will probably not send an operation with code OP_ILLEGAL but
if it does, the response will be ILLEGAL4res just as it would be with
any other invalid operation code. Note that if the server gets an
illegal operation code that is not OP_ILLEGAL, and if the server
checks for legal operation codes during the XDR decode phase, then
the ILLEGAL4res would not be returned.
ERRORS
NFS4ERR_OP_ILLEGAL
The procedures used for callbacks are defined in the following
sections. In the interest of clarity, the terms "client" and
"server" refer to NFS clients and servers, despite the fact that for
an individual callback RPC, the sense of these terms would be
precisely the opposite.
SYNOPSIS
<null>
ARGUMENT
void;
RESULT
void;
DESCRIPTION
Standard NULL procedure. Void argument, void response. Even though
there is no direct functionality associated with this procedure, the
server will use CB_NULL to confirm the existence of a path for RPCs
from server to client.
ERRORS
None.
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SYNOPSIS
compoundargs -> compoundres
ARGUMENT
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4,
OP_CB_ILLEGAL = 10044
};
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR: CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL: CB_RECALL4args opcbrecall;
case OP_CB_ILLEGAL: void opcbillegal;
};
struct CB_COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
uint32_t callback_ident;
nfs_cb_argop4 argarray<>;
};
RESULT
union nfs_cb_resop4 switch (unsigned resop){
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall;
};
struct CB_COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_cb_resop4 resarray<>;
};
DESCRIPTION
The CB_COMPOUND procedure is used to combine one or more of the
callback procedures into a single RPC request. The main callback RPC
program has two main procedures: CB_NULL and CB_COMPOUND. All other
operations use the CB_COMPOUND procedure as a wrapper.
Shepler, et al. Standards Track [Page 226]
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In the processing of the CB_COMPOUND procedure, the client may find
that it does not have the available resources to execute any or all
of the operations within the CB_COMPOUND sequence. In this case, the
error NFS4ERR_RESOURCE will be returned for the particular operation
within the CB_COMPOUND procedure where the resource exhaustion
occurred. This assumes that all previous operations within the
CB_COMPOUND sequence have been evaluated successfully.
Contained within the CB_COMPOUND results is a 'status' field. This
status must be equivalent to the status of the last operation that
was executed within the CB_COMPOUND procedure. Therefore, if an
operation incurred an error then the 'status' value will be the same
error value as is being returned for the operation that failed.
For the definition of the "tag" field, see the section "Procedure 1:
COMPOUND - Compound Operations".
The value of callback_ident is supplied by the client during
SETCLIENTID. The server must use the client supplied callback_ident
during the CB_COMPOUND to allow the client to properly identify the
server.
Illegal operation codes are handled in the same way as they are
handled for the COMPOUND procedure.
IMPLEMENTATION
The CB_COMPOUND procedure is used to combine individual operations
into a single RPC request. The client interprets each of the
operations in turn. If an operation is executed by the client and
the status of that operation is NFS4_OK, then the next operation in
the CB_COMPOUND procedure is executed. The client continues this
process until there are no more operations to be executed or one of
the operations has a status value other than NFS4_OK.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_OP_ILLEGAL
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
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SYNOPSIS
fh, attr_request -> attrmask, attr_vals
ARGUMENT
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
RESULT
struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
DESCRIPTION
The CB_GETATTR operation is used by the server to obtain the
current modified state of a file that has been write delegated.
The attributes size and change are the only ones guaranteed to be
serviced by the client. See the section "Handling of CB_GETATTR"
for a full description of how the client and server are to interact
with the use of CB_GETATTR.
If the filehandle specified is not one for which the client holds a
write open delegation, an NFS4ERR_BADHANDLE error is returned.
IMPLEMENTATION
The client returns attrmask bits and the associated attribute
values only for the change attribute, and attributes that it may
change (time_modify, and size).
Shepler, et al. Standards Track [Page 228]
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ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BADXDR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
SYNOPSIS
stateid, truncate, fh -> ()
ARGUMENT
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
RESULT
struct CB_RECALL4res {
nfsstat4 status;
};
DESCRIPTION
The CB_RECALL operation is used to begin the process of recalling an
open delegation and returning it to the server.
The truncate flag is used to optimize recall for a file which is
about to be truncated to zero. When it is set, the client is freed
of obligation to propagate modified data for the file to the server,
since this data is irrelevant.
If the handle specified is not one for which the client holds an open
delegation, an NFS4ERR_BADHANDLE error is returned.
If the stateid specified is not one corresponding to an open
delegation for the file specified by the filehandle, an
NFS4ERR_BAD_STATEID is returned.
Shepler, et al. Standards Track [Page 229]
RFC 3530 NFS version 4 Protocol April 2003
IMPLEMENTATION
The client should reply to the callback immediately. Replying does
not complete the recall except when an error was returned. The
recall is not complete until the delegation is returned using a
DELEGRETURN.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_BADXDR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
SYNOPSIS
<null> -> ()
ARGUMENT
void;
RESULT
struct CB_ILLEGAL4res {
nfsstat4 status;
};
DESCRIPTION
This operation is a placeholder for encoding a result to handle the
case of the client sending an operation code within COMPOUND that is
not supported. See the COMPOUND procedure description for more
details.
The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
IMPLEMENTATION
A server will probably not send an operation with code OP_CB_ILLEGAL
but if it does, the response will be CB_ILLEGAL4res just as it would
be with any other invalid operation code. Note that if the client
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RFC 3530 NFS version 4 Protocol April 2003
gets an illegal operation code that is not OP_ILLEGAL, and if the
client checks for legal operation codes during the XDR decode phase,
then the CB_ILLEGAL4res would not be returned.
ERRORS
NFS4ERR_OP_ILLEGAL
NFS has historically used a model where, from an authentication
perspective, the client was the entire machine, or at least the
source IP address of the machine. The NFS server relied on the NFS
client to make the proper authentication of the end-user. The NFS
server in turn shared its files only to specific clients, as
identified by the client's source IP address. Given this model, the
AUTH_SYS RPC security flavor simply identified the end-user using the
client to the NFS server. When processing NFS responses, the client
ensured that the responses came from the same IP address and port
number that the request was sent to. While such a model is easy to
implement and simple to deploy and use, it is certainly not a safe
model. Thus, NFSv4 mandates that implementations support a security
model that uses end to end authentication, where an end-user on a
client mutually authenticates (via cryptographic schemes that do not
expose passwords or keys in the clear on the network) to a principal
on an NFS server. Consideration should also be given to the
integrity and privacy of NFS requests and responses. The issues of
end to end mutual authentication, integrity, and privacy are
discussed as part of the section on "RPC and Security Flavor".
Note that while NFSv4 mandates an end to end mutual authentication
model, the "classic" model of machine authentication via IP address
checking and AUTH_SYS identification can still be supported with the
caveat that the AUTH_SYS flavor is neither MANDATORY nor RECOMMENDED
by this specification, and so interoperability via AUTH_SYS is not
assured.
For reasons of reduced administration overhead, better performance
and/or reduction of CPU utilization, users of NFS version 4
implementations may choose to not use security mechanisms that enable
integrity protection on each remote procedure call and response. The
use of mechanisms without integrity leaves the customer vulnerable to
an attacker in between the NFS client and server that modifies the
RPC request and/or the response. While implementations are free to
provide the option to use weaker security mechanisms, there are two
operations in particular that warrant the implementation overriding
user choices.
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The first such operation is SECINFO. It is recommended that the
client issue the SECINFO call such that it is protected with a
security flavor that has integrity protection, such as RPCSEC_GSS
with a security triple that uses either rpc_gss_svc_integrity or
rpc_gss_svc_privacy (rpc_gss_svc_privacy includes integrity
protection) service. Without integrity protection encapsulating
SECINFO and therefore its results, an attacker in the middle could
modify results such that the client might select a weaker algorithm
in the set allowed by server, making the client and/or server
vulnerable to further attacks.
The second operation that should definitely use integrity protection
is any GETATTR for the fs_locations attribute. The attack has two
steps. First the attacker modifies the unprotected results of some
operation to return NFS4ERR_MOVED. Second, when the client follows up
with a GETATTR for the fs_locations attribute, the attacker modifies
the results to cause the client migrate its traffic to a server
controlled by the attacker.
Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
responsible for the release of client state, it is imperative that
the principal used for these operations is checked against and match
the previous use of these operations. See the section "Client ID"
for further discussion.
The NFS version 4 protocol provides for the association of named
attributes to files. The name space identifiers for these attributes
are defined as string names. The protocol does not define the
specific assignment of the name space for these file attributes.
Even though the name space is not specifically controlled to prevent
collisions, an IANA registry has been created for the registration of
NFS version 4 named attributes. Registration will be achieved
through the publication of an Informational RFC and will require not
only the name of the attribute but the syntax and semantics of the
named attribute contents; the intent is to promote interoperability
where common interests exist. While application developers are
allowed to define and use attributes as needed, they are encouraged
to register the attributes with IANA.
The section "Structured Data Types" discussed the r_netid field and
the corresponding r_addr field of a clientaddr4 structure. The NFS
version 4 protocol depends on the syntax and semantics of these
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RFC 3530 NFS version 4 Protocol April 2003
fields to effectively communicate callback information between client
and server. Therefore, an IANA registry has been created to include
the values defined in this document and to allow for future expansion
based on transport usage/availability. Additions to this ONC RPC
Network Identifier registry must be done with the publication of an
RFC.
The initial values for this registry are as follows (some of this
text is replicated from section 2.2 for clarity):
The Network Identifier (or r_netid for short) is used to specify a
transport protocol and associated universal address (or r_addr for
short). The syntax of the Network Identifier is a US-ASCII string.
The initial definitions for r_netid are:
"tcp" - TCP over IP version 4
"udp" - UDP over IP version 4
"tcp6" - TCP over IP version 6
"udp6" - UDP over IP version 6
Note: the '"' marks are used for delimiting the strings for this
document and are not part of the Network Identifier string.
For the "tcp" and "udp" Network Identifiers the Universal Address or
r_addr (for IPv4) is a US-ASCII string and is of the form:
h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for
representing an IPv4 address, which is always four octets long.
Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
the first through fourth octets each converted to ASCII-decimal.
Assuming big-endian ordering, p1 and p2 are, respectively, the first
and second octets each converted to ASCII-decimal. For example, if a
host, in big-endian order, has an address of 0x0A010307 and there is
a service listening on, in big endian order, port 0x020F (decimal
527), then complete universal address is "10.1.3.7.2.15".
For the "tcp6" and "udp6" Network Identifiers the Universal Address
or r_addr (for IPv6) is a US-ASCII string and is of the form:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
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RFC 3530 NFS version 4 Protocol April 2003
The suffix "p1.p2" is the service port, and is computed the same way
as with universal addresses for "tcp" and "udp". The prefix,
"x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
representing an IPv6 address as defined in Section 2.2 of [RFC2373].
Additionally, the two alternative forms specified in Section 2.2 of
[RFC2373] are also acceptable.
As mentioned, the registration of new Network Identifiers will
require the publication of an Information RFC with similar detail as
listed above for the Network Identifier itself and corresponding
Universal Address.
The authors thank and acknowledge:
Neil Brown for his extensive review and comments of various
documents. Rick Macklem at the University of Guelph, Mike Frisch,
Sergey Klyushin, and Dan Trufasiu of Hummingbird Ltd., and Andy
Adamson, Bruce Fields, Jim Rees, and Kendrick Smith from the CITI
organization at the University of Michigan, for their implementation
efforts and feedback on the protocol specification. Mike Kupfer for
his review of the file locking and ACL mechanisms. Alan Yoder for
his input to ACL mechanisms. Peter Astrand for his close review of
the protocol specification. Ran Atkinson for his constant reminder
that users do matter.
[ISO10646] "ISO/IEC 10646-1:1993. International
Standard -- Information technology --
Universal Multiple-Octet Coded Character
Set (UCS) -- Part 1: Architecture and Basic
Multilingual Plane."
[RFC793] Postel, J., "Transmission Control
Protocol", STD 7, RFC 793, September 1981.
[RFC1831] Srinivasan, R., "RPC: Remote Procedure Call
Protocol Specification Version 2", RFC
1831, August 1995.
Shepler, et al. Standards Track [Page 268]
RFC 3530 NFS version 4 Protocol April 2003
[RFC1832] Srinivasan, R., "XDR: External Data
Representation Standard", RFC 1832, August
1995.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6
Addressing Architecture", RFC 2373, July
1998.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API
Mechanism", RFC 1964, June 1996.
[RFC2025] Adams, C., "The Simple Public-Key GSS-API
Mechanism (SPKM)", RFC 2025, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC
2119, March 1997.
[RFC2203] Eisler, M., Chiu, A. and L. Ling,
"RPCSEC_GSS Protocol Specification", RFC
2203, September 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character
Sets and Languages", BCP 19, RFC 2277,
January 1998.
[RFC2279] Yergeau, F., "UTF-8, a transformation
format of ISO 10646", RFC 2279, January
1998.
[RFC2623] Eisler, M., "NFS Version 2 and Version 3
Security Issues and the NFS Protocol's Use
of RPCSEC_GSS and Kerberos V5", RFC 2623,
June 1999.
[RFC2743] Linn, J., "Generic Security Service
Application Program Interface, Version 2,
Update 1", RFC 2743, January 2000.
[RFC2847] Eisler, M., "LIPKEY - A Low Infrastructure
Public Key Mechanism Using SPKM", RFC 2847,
June 2000.
[RFC3010] Shepler, S., Callaghan, B., Robinson, D.,
Thurlow, R., Beame, C., Eisler, M. and D.
Noveck, "NFS version 4 Protocol", RFC 3010,
December 2000.
Shepler, et al. Standards Track [Page 269]
RFC 3530 NFS version 4 Protocol April 2003
[RFC3454] Hoffman, P. and P. Blanchet, "Preparation
of Internationalized Strings
("stringprep")", RFC 3454, December 2002.
[Unicode1] The Unicode Consortium, "The Unicode
Standard, Version 3.0", Addison-Wesley
Developers Press, Reading, MA, 2000. ISBN
0-201-61633-5.
More information available at:
http://www.unicode.org/
[Unicode2] "Unsupported Scripts" Unicode, Inc., The
Unicode Consortium, P.O. Box 700519, San
Jose, CA 95710-0519 USA, September 1999.
http://www.unicode.org/unicode/standard/
unsupported.html
[Floyd] S. Floyd, V. Jacobson, "The Synchronization
of Periodic Routing Messages," IEEE/ACM
Transactions on Networking, 2(2), pp. 122-
136, April 1994.
[Gray] C. Gray, D. Cheriton, "Leases: An Efficient
Fault-Tolerant Mechanism for Distributed
File Cache Consistency," Proceedings of the
Twelfth Symposium on Operating Systems
Principles, p. 202-210, December 1989.
[Juszczak] Juszczak, Chet, "Improving the Performance
and Correctness of an NFS Server," USENIX
Conference Proceedings, USENIX Association,
Berkeley, CA, June 1990, pages 53-63.
Describes reply cache implementation that
avoids work in the server by handling
duplicate requests. More important, though
listed as a side-effect, the reply cache
aids in the avoidance of destructive non-
idempotent operation re-application --
improving correctness.
Shepler, et al. Standards Track [Page 270]
RFC 3530 NFS version 4 Protocol April 2003
[Kazar] Kazar, Michael Leon, "Synchronization and
Caching Issues in the Andrew File System,"
USENIX Conference Proceedings, USENIX
Association, Berkeley, CA, Dallas Winter
1988, pages 27-36. A description of the
cache consistency scheme in AFS.
Contrasted with other distributed file
systems.
[Macklem] Macklem, Rick, "Lessons Learned Tuning the
4.3BSD Reno Implementation of the NFS
Protocol," Winter USENIX Conference
Proceedings, USENIX Association, Berkeley,
CA, January 1991. Describes performance
work in tuning the 4.3BSD Reno NFS
implementation. Describes performance
improvement (reduced CPU loading) through
elimination of data copies.
[Mogul] Mogul, Jeffrey C., "A Recovery Protocol for
Spritely NFS," USENIX File System Workshop
Proceedings, Ann Arbor, MI, USENIX
Association, Berkeley, CA, May 1992.
Second paper on Spritely NFS proposes a
lease-based scheme for recovering state of
consistency protocol.
[Nowicki] Nowicki, Bill, "Transport Issues in the
Network File System," ACM SIGCOMM
newsletter Computer Communication Review,
April 1989. A brief description of the
basis for the dynamic retransmission work.
[Pawlowski] Pawlowski, Brian, Ron Hixon, Mark Stein,
Joseph Tumminaro, "Network Computing in the
UNIX and IBM Mainframe Environment,"
Uniforum `89 Conf. Proc., (1989)
Description of an NFS server implementation
for IBM's MVS operating system.
[RFC1094] Sun Microsystems, Inc., "NFS: Network File
System Protocol Specification", RFC 1094,
March 1989.
[RFC1345] Simonsen, K., "Character Mnemonics &
Character Sets", RFC 1345, June 1992.
Shepler, et al. Standards Track [Page 271]
RFC 3530 NFS version 4 Protocol April 2003
[RFC1813] Callaghan, B., Pawlowski, B. and P.
Staubach, "NFS Version 3 Protocol
Specification", RFC 1813, June 1995.
[RFC3232] Reynolds, J., Editor, "Assigned Numbers:
RFC 1700 is Replaced by an On-line
Database", RFC 3232, January 2002.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC
RPC Version 2", RFC 1833, August 1995.
[RFC2054] Callaghan, B., "WebNFS Client
Specification", RFC 2054, October 1996.
[RFC2055] Callaghan, B., "WebNFS Server
Specification", RFC 2055, October 1996.
[RFC2152] Goldsmith, D. and M. Davis, "UTF-7 A Mail-
Safe Transformation Format of Unicode", RFC
2152, May 1997.
[RFC2224] Callaghan, B., "NFS URL Scheme", RFC 2224,
October 1997.
[RFC2624] Shepler, S., "NFS Version 4 Design
Considerations", RFC 2624, June 1999.
[RFC2755] Chiu, A., Eisler, M. and B. Callaghan,
"Security Negotiation for WebNFS" , RFC
2755, June 2000.
[Sandberg] Sandberg, R., D. Goldberg, S. Kleiman, D.
Walsh, B. Lyon, "Design and Implementation
of the Sun Network Filesystem," USENIX
Conference Proceedings, USENIX Association,
Berkeley, CA, Summer 1985. The basic paper
describing the SunOS implementation of the
NFS version 2 protocol, and discusses the
goals, protocol specification and trade-
offs.
Shepler, et al. Standards Track [Page 272]
RFC 3530 NFS version 4 Protocol April 2003
[Srinivasan] Srinivasan, V., Jeffrey C. Mogul, "Spritely
NFS: Implementation and Performance of
Cache Consistency Protocols", WRL Research
Report 89/5, Digital Equipment Corporation
Western Research Laboratory, 100 Hamilton
Ave., Palo Alto, CA, 94301, May 1989. This
paper analyzes the effect of applying a
Sprite-like consistency protocol applied to
standard NFS. The issues of recovery in a
stateful environment are covered in
[Mogul].
[XNFS] The Open Group, Protocols for Interworking:
XNFS, Version 3W, The Open Group, 1010 El
Camino Real Suite 380, Menlo Park, CA
94025, ISBN 1-85912-184-5, February 1998.
HTML version available:
http://www.opengroup.org
Carl Beame
Hummingbird Ltd.
EMail: beame@bws.com
Brent Callaghan
Sun Microsystems, Inc.
17 Network Circle
Menlo Park, CA 94025
Phone: +1 650-786-5067
EMail: brent.callaghan@sun.com
Mike Eisler
5765 Chase Point Circle
Colorado Springs, CO 80919
Phone: +1 719-599-9026
EMail: mike@eisler.com
David Noveck
Network Appliance
375 Totten Pond Road
Waltham, MA 02451
Phone: +1 781-768-5347
EMail: dnoveck@netapp.com
David Robinson
Sun Microsystems, Inc.
5300 Riata Park Court
Austin, TX 78727
Phone: +1 650-786-5088
EMail: david.robinson@sun.com
Robert Thurlow
Sun Microsystems, Inc.
500 Eldorado Blvd.
Broomfield, CO 80021
Phone: +1 650-786-5096
EMail: robert.thurlow@sun.com
Shepler, et al. Standards Track [Page 274]
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Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Shepler, et al. Standards Track [Page 275]