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 discipline manipulating a real tty structure declared by a real device driver.  The /dev/sxt driver is currently only used by the shl(1) command.

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 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. 

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

SEE ALSO

shl(1), stty(1), termio(7). 
ioctl(2), open(2) in the INTER­ACTIVE SDS Guide and Programmer’s Reference Manual. 

\*U  —  Version 1.0