NAME
ioctl — control device
SYNOPSIS
#include <stropts.h>
int ioctl(int fildes, int request, ... /* arg */);
Remarks
The ANSI C ", ..." construct denotes a variable length argument list whose
optional [or required]
members are given in the associated comment
(/* */).
DESCRIPTION
ioctl()
performs a variety of functions on character special files (devices),
or regular files and directories on
VxFS
file systems.
The write-ups of various devices in Section (7) discuss how
ioctl()
applies to them.
The type of
arg
is dependent on the specific
ioctl()
call, as described in Section (7).
request
is made up of several fields
which encode the size and direction of the argument (referenced by
arg),
as well as the desired command.
An enumeration of the request fields are:
- IOC_IN
Argument is read by the driver
(meaning that the argument is copied from the application to the driver).
- IOC_OUT
Argument is written by the driver
(meaning that the argument is copied from the driver to the application).
Ignored if an error occurs.
- IOCSIZE_MASK
Number of bytes in the passed argument.
A nonzero size indicates that
arg
is a pointer to the passed argument.
A zero size indicates that
arg
is the passed argument (if the driver wants to use it),
and is not treated as a pointer.
- IOCCMD_MASK
The request command itself.
When both
IOC_IN
and
IOC_OUT
are zero, it can be assumed that
request
is not encoded for size and direction, for compatibility purposes.
Requests that do not require any data to be passed
and requests that use
arg
as a value (as opposed to a pointer), have the
IOC_IN
bit set to one and the
IOCSIZE_MASK
field set to zero.
The following macros are used to create the request argument.
x
and
y
are concatenated
((x<<8) | y)
to form
IOCCMD
and shifted into the proper location according to
IOCCMD_MASK.
t
is the type (e.g.
struct routeaddrs)
of the actual argument that the request references,
and its size is taken and shifted into the appropriate place according to
IOCSIZE_MASK.
- _IOR(x,y,t)
Sets
IOC_OUT
and initializes the values at
IOCCMD_MASK
and
IOCSIZE_MASK
accordingly.
- _IOW(x,y,t)
Sets
IOC_IN
and initializes the values at
IOCCMD_MASK
and
IOCSIZE_MASK
accordingly.
- _IOWR(x,y,t)
Sets both
IOC_IN
and
IOC_OUT
and initializes the values at
IOCCMD_MASK
and
IOCSIZE_MASK.
Note: any data structure referenced by
arg
must
not
contain any pointers.
RETURN VALUE
If an error has occurred, a value of -1 is returned and
errno
is set to indicate the error.
ioctl()
fails if one or more of the following are true:
IOC_OUT
is ignored if an error occurs.
- [EBADF]
fildes
is not a valid open file descriptor.
- [ENOTTY]
The request is not appropriate to the selected device.
- [EINVAL]
request
or
arg
is not valid.
- [EINTR]
A signal was caught during the
ioctl()
system call.
- [EPERM]
Typically this error indicates that an ioctl request was attempted
that is forbidden in some way to the calling process.
AUTHOR
ioctl()
was developed by
AT&T and HP.
STANDARDS CONFORMANCE
ioctl(): SVID2, SVID3, XPG2
Printable version
