Print this page
14249 pseudo-terminal nomenclature should reflect POSIX
Change-Id: Ib4a3cef899ff4c71b09cb0dc6878863c5e8357bc
@@ -1,99 +1,151 @@
-PTS(7D) Devices PTS(7D)
+PTM(7D) Devices PTM(7D)
NAME
- pts - STREAMS pseudo-tty slave driver
+ ptm, pts - STREAMS pseudo-terminal manager and subsidiary drivers
+SYNOPSIS
+ /dev/ptmx
+
+ /dev/pts/*
+
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.
+ The pseudo-terminal subsystem simulates a terminal connection, where the
+ manager side represents the terminal and the subsidiary represents the
+ user process's special device end point. The manager 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; see
+ CLONE_DEV in ddi_create_minor_node(9F).
+ There are no nodes in the file system for manager devices. The manager
+ 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.
- 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. Unless compiled in XPG4v2 mode (see below),
- the consumer needs to push the ptem(7M) and ldterm(7M) modules onto the
- slave side of the pseudo-terminal subsystem to get terminal semantics.
+ A manager device is only available if it and its corresponding subsidiary
+ device are not already open. Only one open is allowed on a manager
+ device. Multiple opens are allowed on the subsidiary device.
+ When the manager device is opened, the corresponding subsidiary device is
+ automatically locked out. No user may open the subsidiary device until
+ its permissions are adjusted and the device is unlocked by calling the
+ functions grantpt(3C) and unlockpt(3C). The user can then invoke the
+ open(2) system call with the device name returned by the ptsname(3C)
+ function.
- The master and slave drivers pass all messages to their adjacent
+ After both the manager and subsidiary 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 manager
+ and subsidiary drivers. The user may then push modules onto either side
+ of the stream pair. Unless compiled in XPG4v2 mode (see XPG4v2 MODE),
+ the consumer needs to push the ptem(7M) and ldterm(7M) modules onto the
+ subsidiary device to get terminal semantics.
+
+ The manager and subsidiary 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. 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 side
- should not write 0-length messages. Unless the application is compiled
- in XPG4v2 mode (see below) then any 0-length messages written on the
- slave side will be discarded by the ptem module.
+ 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 manager device is closed, an M_HANGUP message is sent to the
+ subsidiary device which will render the device unusable. The process on
+ the subsidiary side gets an EIO error 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(2) returns 0
+ indicating that the stream can no longer be used.
- The standard STREAMS system calls can access the pseudo-tty devices.
- The slave devices support the O_NDELAY and O_NONBLOCK flags.
+ On the last close of the subsidiary device, a 0-length message is sent to
+ the manager device. When the application on the manager side issues a
+ read(2) or getmsg(2) and 0 is returned, the user of the manager device
+ decides whether to issue a close(2) that dismantles the entire pseudo-
+ terminal. If the manager device is not closed, the pseudo-terminal will
+ be available to another user to open the subsidiary device.
+ Since 0-length messages are used to indicate that the process on the
+ subsidiary side has closed, and should be interpreted that way by the
+ process on the manager side, applications on the subsidiary side should
+ not write 0-length messages. Unless the application is compiled in
+ XPG4v2 mode (see XPG4v2 MODE), then any 0-length messages written to the
+ subsidiary device will be discarded by the ptem(7M) module.
+
+ If O_NONBLOCK or O_NDELAY is set on the manager side:
+
+ o Read on the manager side returns -1 with errno set to EAGAIN if no
+ data is available
+
+ o Write returns -1 with errno set to EAGAIN if there is internal flow
+ control
+
+ Standard STREAMS system calls can access pseudo-terminal devices. The
+ subsidiary devices support the O_NDELAY and O_NONBLOCK flags.
+
XPG4v2 MODE
- XPG4v2 requires that open of a slave pseudo terminal device provides
- the process with an interface that is identical to the terminal
- interface (without having to explicitly push any modules to achieve
- this). It also requires that 0-length messages written on the slave
- side will be propagated to the master.
+ XPG4v2 requires that subsidiary pseudo-terminal devices provide the
+ process with an interface that is identical to the terminal interface,
+ without needing to explicitly push any modules to achieve this. It also
+ requires that 0-length messages written on the subsidiary device will be
+ propagated to the manager device.
- Experience has shown, however, that most software does not expect slave
- pty devices to operate in this manner and therefore this
- XPG4v2-compliant behaviour is only enabled in XPG4v2/SUS (see
- standards(5)) mode.
+ Experience has shown that most software does not expect subsidiary
+ pseudo-terminal devices to operate in this manner. This XPG4v2-compliant
+ behaviour is only enabled in XPG4v2/SUS (see standards(5)) mode.
-EXAMPLES
- int fdm fds;
- char *slavename;
- extern char *ptsname();
+IOCTLS
+ The manager driver provides several ioctls to support the grantpt(3C),
+ unlockpt(3C), and ptsname(3C) functions:
- fdm = open("/dev/ptmx", O_RDWR); /* open master */
- grantpt(fdm); /* change permission of slave */
- unlockpt(fdm); /* unlock slave */
- slavename = ptsname(fdm); /* get name of slave */
- fds = open(slavename, O_RDWR); /* open slave */
- ioctl(fds, I_PUSH, "ptem"); /* push ptem */
- ioctl(fds, I_PUSH, "ldterm"); /* push ldterm*/
+ ISPTM Determines whether the file descriptor is that of an open manager
+ device. On success, it returns the value 0.
+ UNLKPT Unlocks the manager and subsidiary devices. It returns 0 on
+ success. On failure, errno is set to EINVAL indicating that the
+ manager device is not open.
FILES
- /dev/ptmx
- master clone device
+ /dev/ptmx Pseudo-terminal manager clone device.
+ /dev/pts/N Pseudo-terminal subsidiary devices,
+ where N is a non-negative integer.
+ Located via calls to ptsname(3C).
- /dev/pts/M
- slave devices (M = 0 -> N-1)
+EXAMPLES
+ Example 1 Opening the manager and subsidiary device for a pseudo-
+ terminal.
+ #include <stdlib.h>
+ #include <sys/types.h>
+ #include <sys/stat.h>
+ #include <unistd.h>
+ #include <stropts.h>
+ #include <fcntl.h>
+ #include <err.h>
+ ...
+ int fdm, fds;
+ char *subsidiaryname;
+ ...
+ /*
+ * NOTE: Portable applications should use posix_openpt(3C) here:
+ */
+ if ((fdm = open("/dev/ptmx", O_RDWR | O_NOCTTY)) < 0) {
+ err(1, "open manager");
+ }
+ if (grantpt(fdm) != 0 || unlockpt(fdm) != 0 ||
+ (subsidiaryname = ptsname(fdm)) == NULL) {
+ close(fdm);
+ err(1, "locate subsidiary");
+ }
+ if ((fds = open(subsidiaryname, O_RDWR | O_NOCTTY)) < 0) {
+ close(fdm);
+ err(1, "open subsidiary");
+ }
+ if (ioctl(fds, I_PUSH, "ptem") != 0 ||
+ ioctl(fds, I_PUSH, "ldterm") != 0) {
+ close(fds);
+ close(fdm);
+ err(1, "push modules");
+ }
SEE ALSO
- grantpt(3C), ptsname(3C), unlockpt(3C), ldterm(7M), ptm(7D), ptem(7M),
- standards(5)
+ close(2), getmsg(2), open(2), read(2), grantpt(3C), posix_openpt(3C),
+ ptsname(3C), unlockpt(3C), standards(5), ldterm(7M), pckt(7M), ptem(7M),
+ ddi_create_minor_node(9F)
-
- STREAMS Programming Guide
-
- February 29, 2020 PTS(7D)
+illumos February 5, 2022 illumos