1 PTM(7D) Devices PTM(7D)
2
3 NAME
4 ptm, pts - STREAMS pseudo-terminal manager and subsidiary drivers
5
6 SYNOPSIS
7 /dev/ptmx
8
9 /dev/pts/*
10
11 DESCRIPTION
12 The pseudo-terminal subsystem simulates a terminal connection, where the
13 manager side represents the terminal and the subsidiary represents the
14 user process's special device end point. The manager device is set up as
15 a cloned device where its major device number is the major for the clone
16 device and its minor device number is the major for the ptm driver; see
17 CLONE_DEV in ddi_create_minor_node(9F).
18
19 There are no nodes in the file system for manager devices. The manager
20 pseudo driver is opened using the open(2) system call with /dev/ptmx as
21 the device parameter. The clone open finds the next available minor
22 device for the ptm major device.
23
24 A manager device is only available if it and its corresponding subsidiary
25 device are not already open. Only one open is allowed on a manager
26 device. Multiple opens are allowed on the subsidiary device.
27
28 When the manager device is opened, the corresponding subsidiary device is
29 automatically locked out. No user may open the subsidiary device until
30 its permissions are adjusted and the device is unlocked by calling the
31 functions grantpt(3C) and unlockpt(3C). The user can then invoke the
32 open(2) system call with the device name returned by the ptsname(3C)
33 function.
34
35 After both the manager and subsidiary have been opened, the user has two
36 file descriptors which are the end points of a full duplex connection
37 composed of two streams which are automatically connected at the manager
38 and subsidiary drivers. The user may then push modules onto either side
39 of the stream pair. Unless compiled in XPG4v2 mode (see XPG4v2 MODE),
40 the consumer needs to push the ptem(7M) and ldterm(7M) modules onto the
41 subsidiary device to get terminal semantics.
42
43 The manager and subsidiary drivers pass all messages to their adjacent
44 queues. Only the M_FLUSH needs some processing. Because the read queue
45 of one side is connected to the write queue of the other, the FLUSHR flag
46 is changed to the FLUSHW flag and vice versa.
47
48 When the manager device is closed, an M_HANGUP message is sent to the
49 subsidiary device which will render the device unusable. The process on
50 the subsidiary side gets an EIO error when attempting to write on that
51 stream, but it will be able to read any data remaining on the stream head
52 read queue. When all the data has been read, read(2) returns 0
53 indicating that the stream can no longer be used.
54
55 On the last close of the subsidiary device, a 0-length message is sent to
56 the manager device. When the application on the manager side issues a
57 read(2) or getmsg(2) and 0 is returned, the user of the manager device
58 decides whether to issue a close(2) that dismantles the entire pseudo-
59 terminal. If the manager device is not closed, the pseudo-terminal will
60 be available to another user to open the subsidiary device.
61
62 Since 0-length messages are used to indicate that the process on the
63 subsidiary side has closed, and should be interpreted that way by the
64 process on the manager side, applications on the subsidiary side should
65 not write 0-length messages. Unless the application is compiled in
66 XPG4v2 mode (see XPG4v2 MODE), then any 0-length messages written to the
67 subsidiary device will be discarded by the ptem(7M) module.
68
69 If O_NONBLOCK or O_NDELAY is set on the manager side:
70
71 o Read on the manager side returns -1 with errno set to EAGAIN if no
72 data is available
73
74 o Write returns -1 with errno set to EAGAIN if there is internal flow
75 control
76
77 Standard STREAMS system calls can access pseudo-terminal devices. The
78 subsidiary devices support the O_NDELAY and O_NONBLOCK flags.
79
80 XPG4v2 MODE
81 XPG4v2 requires that subsidiary pseudo-terminal devices provide the
82 process with an interface that is identical to the terminal interface,
83 without needing to explicitly push any modules to achieve this. It also
84 requires that 0-length messages written on the subsidiary device will be
85 propagated to the manager device.
86
87 Experience has shown that most software does not expect subsidiary
88 pseudo-terminal devices to operate in this manner. This XPG4v2-compliant
89 behaviour is only enabled in XPG4v2/SUS (see standards(5)) mode.
90
91 IOCTLS
92 The manager driver provides several ioctls to support the grantpt(3C),
93 unlockpt(3C), and ptsname(3C) functions:
94
95 ISPTM Determines whether the file descriptor is that of an open manager
96 device. On success, it returns the value 0.
97
98 UNLKPT Unlocks the manager and subsidiary devices. It returns 0 on
99 success. On failure, errno is set to EINVAL indicating that the
100 manager device is not open.
101
102 FILES
103 /dev/ptmx Pseudo-terminal manager clone device.
104
105 /dev/pts/N Pseudo-terminal subsidiary devices,
106 where N is a non-negative integer.
107 Located via calls to ptsname(3C).
108
109 EXAMPLES
110 Example 1 Opening the manager and subsidiary device for a pseudo-
111 terminal.
112
113 #include <stdlib.h>
114 #include <sys/types.h>
115 #include <sys/stat.h>
116 #include <unistd.h>
117 #include <stropts.h>
118 #include <fcntl.h>
119 #include <err.h>
120 ...
121 int fdm, fds;
122 char *subsidiaryname;
123 ...
124 /*
125 * NOTE: Portable applications should use posix_openpt(3C) here:
126 */
127 if ((fdm = open("/dev/ptmx", O_RDWR | O_NOCTTY)) < 0) {
128 err(1, "open manager");
129 }
130 if (grantpt(fdm) != 0 || unlockpt(fdm) != 0 ||
131 (subsidiaryname = ptsname(fdm)) == NULL) {
132 close(fdm);
133 err(1, "locate subsidiary");
134 }
135 if ((fds = open(subsidiaryname, O_RDWR | O_NOCTTY)) < 0) {
136 close(fdm);
137 err(1, "open subsidiary");
138 }
139 if (ioctl(fds, I_PUSH, "ptem") != 0 ||
140 ioctl(fds, I_PUSH, "ldterm") != 0) {
141 close(fds);
142 close(fdm);
143 err(1, "push modules");
144 }
145
146 SEE ALSO
147 close(2), getmsg(2), open(2), read(2), grantpt(3C), posix_openpt(3C),
148 ptsname(3C), unlockpt(3C), standards(5), ldterm(7M), pckt(7M), ptem(7M),
149 ddi_create_minor_node(9F)
150
151 illumos February 5, 2022 illumos