NAME
pckt — Packet Mode module for STREAMS pty (pseudo-terminal)
SYNOPSIS
#include <sys/stropts.h>
int ioctl(fd_slave, I_PUSH, "pckt");
DESCRIPTION
The
Packet
Mode
feature for STREAMS pty devices allows the user process on the master
side of the pty device to be informed of state changes in the pty.
To enable
Packet
Mode
in the STREAMS pty device, the user process must push
the
pckt
module onto the master side of the pty with a call to the
STREAMS
I_PUSH
ioctl(2)
system call. When the
pckt
module is pushed onto a STREAMS pty master, certain STREAMS messages going
upstream on the master side will get packetized so they can be subsequently
retrieved by the master side with a
getmsg
function.
When the user process writes data, the
pckt
module passes the message unchanged downstream on to the next module or driver.
When the user process reads data or when the
pckt
module
receives certain STREAMS message types, it constructs a packet out of the
message for forwarding upstream.
To construct a message packet, the module creates an
M_PROTO
message. This
M_PROTO
message contains the original message type in the first
data block and the original message in as many data blocks as needed.
The user process can then retrieve the
M_PROTO
message with a call to the
getmsg()
function.
The
pckt
module packetizes the following STREAMS message types:
M_DATA,
M_IOCTL,
M_PROTO,
M_PCPROTO,
M_FLUSH,
M_START,
M_STOP,
M_STARTI,
M_STOPI,
M_READ.
All other messages are passed unchanged upstream.
If the message is an
M_FLUSH
message, the
pckt
module looks at the flag and takes the following actions:
If the flag is
FLUSHW,
the module changes it to
FLUSHR
before creating the
M_PROTO
message and passing the message upstream.
This prevents the stream head's read queue from being flushed by the original
M_FLUSHmessage.
If the flag is
FLUSHR,
the module changes it to
FLUSHW
before creating the
M_PROTO
message and passing it upstream.
To flush the write queues properly, the module also sends an
M_FLUSH
message with the
FLUSHW
flag set.
If the flag is
FLUSHRW,
the module changes it to
FLUSHW
before creating the
M_PROTO
message and passing it upstream.
To flush the write queues properly, the module also sends an
M_FLUSH
message with the
FLUSHW
flag set.
AUTHOR
pckt(7)
was developed by HP and OSF.
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