Devices pts(7D)
NAME
pts - STREAMS pseudo-tty slave 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 nodes for the slave driver (N is
determined at installation time) must be installed. The
names of the slave devices are /dev/pts/M where M has the
values 0 through N-1. When the master device is opened, the
corresponding slave device is automatically locked out. No
user may open that slave device until its permissions are
adjusted and the device unlocked by calling functions
grantpt(3C) and unlockpt(3C). The user can then invoke the
open system call with the name that is returned by the
ptsname(3C) function. See the example below.
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 end points of a full duplex connection composed of
two streams automatically connected at the master and slave
drivers. The user may then push modules onto either side of
the stream pair. The user needs to push the ptem(7M) and
ldterm(7M) modules onto the slave side of the pseudo-
terminal subsystem to get terminal semantics.
The master and slave drivers pass all messages to their
adjacent queues. Only the MFLUSH 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
MHANGUP 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 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. Since
0-length messages are used to indicate that the process on
the slave side has closed and should be interpreted that way
by the process on the master side, applications on the slave
SunOS 5.11 Last change: 21 Aug 1992 1
Devices pts(7D)
side should not write 0-length messages. If that occurs, the
write returns 0, and the 0-length message is discarded by
the ptem module.
The standard STREAMS system calls can access the pseudo-tty
devices. The slave devices support the ONDELAY and
ONONBLOCK flags.
EXAMPLES
int fdm fds;
char *slavename;
extern char *ptsname();
fdm = open("/dev/ptmx", ORDWR); /* open master */
grantpt(fdm); /* change permission of slave */
unlockpt(fdm); /* unlock slave */
slavename = ptsname(fdm); /* get name of slave */
fds = open(slavename, ORDWR); /* open slave */
ioctl(fds, IPUSH, "ptem"); /* push ptem */
ioctl(fds, IPUSH, "ldterm"); /* push ldterm*/
FILES
/dev/ptmx master clone device
/dev/pts/M slave devices (M = 0 -> N-1)
SEE ALSO
grantpt(3C), ptsname(3C), unlockpt(3C), ldterm(7M), ptm(7D),
ptem(7M)
STREAMS Programming Guide
SunOS 5.11 Last change: 21 Aug 1992 2
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