Technical data

SunOS 5.5 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 master 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 corresponding 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 connection 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, theFLUSHR 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
ENXIO 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 mas-
ter 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 andUNLKPT 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 major/minor
number of the master device which can be used to determine the name of the correspond-
ing slave device. The ioctlUNLKPT unlocks the master and slave devices. It returns 0 on
success. On failure, the errno is set to EINVAL indicatingthat the master device is not
open.
modified 23 Feb 1994 7D-263