'\" te
.\"  Copyright (c) 1997, Sun Microsystems, Inc.
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.TH ptm 7D "5 Feb 1997" "SunOS 5.11" "Devices"
.SH NAME
ptm \- STREAMS pseudo-tty master driver
.SH DESCRIPTION
.sp
.LP
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 \fB/dev/ptmx\fR and \fBN\fR number of nodes for the slave
driver must be installed. See \fBpts\fR(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 \fBptm\fR driver. There are no
nodes in the file system for master devices. The master pseudo driver is opened
using the \fBopen\fR(2) system call with \fB/dev/ptmx\fR as the device
parameter. The clone open finds the next available minor device for the
\fBptm\fR major device.
.sp
.LP
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.
.sp
.LP
The master and slave drivers pass all messages to their adjacent queues. Only
the \fBM_FLUSH\fR needs some processing. Because the read queue of one side is
connected to the write queue of the other, the \fBFLUSHR\fR flag is changed to
the \fBFLUSHW\fR flag and vice versa. When the master device is closed an
\fBM_HANGUP\fR message is sent to the slave device which will render the device
unusable. The process on the slave side gets the errno \fBEIO\fR 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,
\fBread()\fR 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 \fBread()\fR or
\fBgetmsg()\fR and 0 is returned, the user of the master device decides whether
to issue a \fBclose()\fR 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.
.sp
.LP
If \fBO_NONBLOCK\fR or \fBO_NDELAY\fR is set, read on the master side returns
\(mi1 with errno set to \fBEAGAIN\fR if no data is available, and write returns
\(mi1 with errno set to \fBEAGAIN\fR if there is internal flow control.
.SH IOCTLS
.sp
.LP
The master driver supports the \fBISPTM\fR and \fBUNLKPT\fR ioctls that are
used by the functions \fBgrantpt\fR(3C), \fBunlockpt\fR(3C) and
\fBptsname\fR(3C). The ioctl \fBISPTM\fR determines whether the file descriptor
is that of an open master device. On success, it returns the 0. The ioctl
\fBUNLKPT\fR unlocks the master and slave devices. It returns 0 on success. On
failure, the errno is set to \fBEINVAL\fR indicating that the master device is
not open.
.SH FILES
.sp
.ne 2
.mk
.na
\fB\fB/dev/ptmx\fR\fR
.ad
.RS 14n
.rt  
master clone device
.RE

.sp
.ne 2
.mk
.na
\fB\fB/dev/pts/M\fR\fR
.ad
.RS 14n
.rt  
slave devices (M = 0 -> N-1)
.RE

.SH SEE ALSO
.sp
.LP
\fBgrantpt\fR(3C), \fBptsname\fR(3C), \fBunlockpt\fR(3C), \fBpckt\fR(7M),
\fBpts\fR(7D)
.sp
.LP
\fISTREAMS Programming Guide\fR