ptm(7D) 							      Devices								   ptm(7D)

NAME

       ptm - STREAMS pseudo-tty master driver

DESCRIPTION

       The  pseudo-tty	subsystem simulates a terminal connection, where the master side represents the terminal and the slave represents the user
       process's special device end point. In order to use the pseudo-tty subsystem, a node for the master side driver /dev/ptmx and N	number	of
       nodes for the slave driver must be installed. See pts(7D). The master device is set up as a  cloned device where its major device number is
       the major for the clone device and its minor device number is the major for the ptm driver. There are no nodes in the file system for  mas-
       ter  devices. The master pseudo driver is opened using the open(2) system call with /dev/ptmx as the device parameter. The clone open finds
       the next available minor device for the ptm major device.

       A master device is available only if it and its corresponding slave device are not already open. When the master device is opened, the cor-
       responding  slave device is automatically locked out. Only one open is allowed on a master device.  Multiple opens are allowed on the slave
       device. After both the master and slave have been opened, the user has two file descriptors which are the end points of a full duplex  con-
       nection	composed  of  two  streams  which are automatically connected at the master and slave drivers. The user may then push modules onto
       either side of the stream pair.

       The master and slave drivers pass all messages to their adjacent queues. Only the M_FLUSH needs some processing. Because the read queue	of
       one side is connected to the write queue of the other, the FLUSHR flag is changed to the FLUSHW flag and vice versa. When the master device
       is closed an M_HANGUP message is sent to the slave device which will render the device unusable. The process on the  slave  side  gets  the
       errno  EIO  when  attempting to write on that stream but it will be able to read any data remaining on the stream head read queue. When all
       the data has been read, read() returns 0 indicating that the stream can no longer be used. On  the  last  close	of  the  slave	device,  a
       0-length  message  is sent to the master device. When the application on the master side issues a read() or getmsg() and 0 is returned, the
       user of the master device decides whether to issue a close() that dismantles the pseudo-terminal subsystem. If the  master  device  is  not
       closed, the pseudo-tty subsystem will be available to another user to open the slave device.

       If O_NONBLOCK or O_NDELAY is set, read on the master side returns -1 with errno set to EAGAIN if no data is available, and write returns -1
       with errno set to EAGAIN if there is internal flow control.

IOCTLS

       The master driver supports the ISPTM and UNLKPT ioctls that are used by the functions grantpt(3C), unlockpt(3C) and ptsname(3C). The  ioctl
       ISPTM  determines  whether the file descriptor is that of an open master device. On success, it returns the 0. The ioctl UNLKPT unlocks the
       master and slave devices. It returns 0 on success. On failure, the errno is set to EINVAL indicating that the master device is not open.

FILES

       /dev/ptmx     master clone device

       /dev/pts/M    slave devices (M = 0 -> N-1)

SEE ALSO

       grantpt(3C), ptsname(3C), unlockpt(3C), pckt(7M), pts(7D)

       STREAMS Programming Guide

SunOS 5.11							    5 Feb 1997								   ptm(7D)