SXT(M) UNIX System V SXT(M)
Name
sxt - Pseudo-device driver
Description
Sxt is a pseudo-device driver that interposes a discipline
between the standard tty line disciplines and a real device
driver. The standard disciplines manipulate virtual tty
structures (channels) declared by the sxt driver. Sxt acts
as a discipline manipulating a real tty structure declared
by a real device driver. The sxt driver is currently only
used by the shl(C) command.
Virtual ttys are named /dev/sxt??? and are allocated in
groups of up to eight. To allocate a group, a program
should exclusively open a file with a name of the form
/dev/sxt??0 (channel 0) and then execute a SXTIOCLINK ioctl
call to initiate the multiplexing.
Only one channel, the controlling channel, can receive input
from the keyboard at a time; others attempting to read will
be blocked.
There are two groups of ioctl(S) commands supported by sxt.
The first group contains the standard ioctl commands
described in termio(M), with the addition of the following:
TIOCEXCL Set exclusive use mode: no further opens are
permitted until the file has been closed.
TIOCNXCL Reset exclusive use mode: further opens are
once again permitted.
The second group are directives to sxt itself. Some of
these may only be executed on channel 0.
SXTIOCLINK Allocate a channel group and multiplex
the virtual ttys onto the real tty. The
argument is the number of channels to
allocate. This command may only be
executed on channel 0. Possible errors
include:
EINVAL The argument is out of range.
ENOTTY The command was not issued from a
real tty.
ENXIO linesw is not configured with sxt.
EBUSY An SXTIOCLINK command has already
been issued for this real tty.
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SXT(M) UNIX System V SXT(M)
ENOMEM There is no system memory
available for allocating the
virtual tty structures.
EBADF Channel 0 was not opened before
this call.
SXTIOCSWTCH Set the controlling channel. Possible
errors include:
EINVAL An invalid channel number was
given.
EPERM The command was not executed from
channel 0.
SXTIOCWF Cause a channel to wait until it is the
controlling channel. This command will
return the error, EINVAL, if an invalid
channel number is given.
SXTIOCUBLK Turn off the loblk control flag in the
virtual tty of the indicated channel. The
error EINVAL will be returned if an
invalid number or channel 0 is given.
SXTIOCSTAT Get the status (blocked on input or
output) of each channel and store in the
sxtblock structure referenced by the
argument. The error EFAULT will be
returned if the structure cannot be
written.
SXTIOCTRACE Enable tracing. Tracing information is
written to the console. This command has
no effect if tracing is not configured.
SXTIOCNOTRACE
Disable tracing. This command has no
effect if tracing is not configured.
FILES
/dev/sxt??[0-7] virtual tty devices
/usr/include/sys/sxt.h driver specific definitions
SEE ALSO
shl(C), stty(C), ioctl(S), open(S), termio(M)
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