sxt(7)                                                               sxt(7)

NAME
     sxt - pseudo-device driver

DESCRIPTION
     The special file /dev/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 /dev/sxt driver. /dev/sxt acts as a discip-
     line manipulating a real tty structure declared by a real device
     driver. The /dev/sxt driver is currently only used by the shl(1) com-
     mand.

     Virtual ttys are named by inodes in the subdirectory /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(2) commands supported by sxt. The first
     group contains the standard ioctl commands described in termio(7),
     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 commands 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 chan-
                    nels 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.

                    ENOMEM    There is no system memory available for allo-
                              cating the virtual tty structures.

                    EBADF     Channel 0 was not opened before this call.



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sxt(7)                                                               sxt(7)

     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.

FILES
     /dev/sxt/??[0-7]
          Virtual tty devices

SEE ALSO
     shl(1), stty(1), ioctl(2), open(2), termio(7).





























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