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7 .\" Copyright 2022 Oxide Computer Company
8 .Dd February 5, 2022
9 .Dt PTM 7D
10 .Os
11 .Sh NAME
12 .Nm ptm ,
13 .Nm pts
14 .Nd STREAMS pseudo-terminal manager and subsidiary drivers
15 .Sh SYNOPSIS
16 .Pa /dev/ptmx
17 .Pp
18 .Pa /dev/pts/*
19 .Sh DESCRIPTION
20 The pseudo-terminal subsystem simulates a terminal connection, where the
21 manager side represents the terminal and the subsidiary represents the user
22 process's special device end point.
23 The manager device is set up as a cloned device where its major device number
24 is the major for the clone device and its minor device number is the major for
25 the
26 .Nm ptm
27 driver; see
28 .Dv CLONE_DEV
29 in
30 .Xr ddi_create_minor_node 9F .
31 .Pp
32 There are no nodes in the file system for manager devices.
33 The manager pseudo driver is opened using the
34 .Xr open 2
35 system call with
36 .Pa /dev/ptmx
37 as the device parameter.
38 The clone open finds the next available minor device for the
39 .Nm ptm
40 major device.
41 .Pp
42 A manager device is only available if it and its corresponding subsidiary
43 device are not already open.
44 Only one open is allowed on a manager device.
45 Multiple opens are allowed on the subsidiary device.
46 .Pp
47 When the manager device is opened, the corresponding subsidiary device is
48 automatically locked out.
49 No user may open the subsidiary device until its permissions are adjusted and
50 the device is unlocked by calling the functions
51 .Xr grantpt 3C
52 and
53 .Xr unlockpt 3C .
54 The user can then invoke the
55 .Xr open 2
56 system call with the device name returned by the
57 .Xr ptsname 3C
58 function.
59 .Pp
60 After both the manager and subsidiary have been opened, the user has two file
61 descriptors which are the end points of a full duplex connection composed of
62 two streams which are automatically connected at the manager and subsidiary
63 drivers.
64 The user may then push modules onto either side of the stream pair.
65 Unless compiled in XPG4v2 mode
66 .Po
67 see
68 .Sx "XPG4v2 MODE"
69 .Pc ,
70 the consumer needs to push the
71 .Xr ptem 7M
72 and
73 .Xr ldterm 7M
74 modules onto the subsidiary device to get terminal semantics.
75 .Pp
76 The manager and subsidiary drivers pass all messages to their adjacent queues.
77 Only the
78 .Dv M_FLUSH
79 needs some processing.
80 Because the read queue of one side is connected to the write queue of the
81 other, the
82 .Dv FLUSHR
83 flag is changed to the
84 .Dv FLUSHW
85 flag and vice versa.
86 .Pp
87 When the manager device is closed, an
88 .Dv M_HANGUP
89 message is sent to the subsidiary device which will render the device unusable.
90 The process on the subsidiary side gets an
91 .Er EIO
92 error when attempting to write on that stream, but it will be able to read
93 any data remaining on the stream head read queue.
94 When all the data has been read,
95 .Xr read 2
96 returns
97 .Sy 0
98 indicating that the stream can no longer be used.
99 .Pp
100 On the last close of the subsidiary device, a 0-length message is sent to the
101 manager device.
102 When the application on the manager side issues a
103 .Xr read 2
104 or
105 .Xr getmsg 2
106 and
107 .Sy 0
108 is returned, the user of the manager device decides whether to issue a
109 .Xr close 2
110 that dismantles the entire pseudo-terminal.
111 If the manager device is not closed, the pseudo-terminal will be available to
112 another user to open the subsidiary device.
113 .Pp
114 Since 0-length messages are used to indicate that the process on the
115 subsidiary side has closed, and should be interpreted that way by the process
116 on the manager side, applications on the subsidiary side should not write
117 0-length messages.
118 Unless the application is compiled in XPG4v2 mode
119 .Po
120 see
121 .Sx "XPG4v2 MODE"
122 .Pc ,
123 then any 0-length messages written to the subsidiary device will be discarded
124 by the
125 .Xr ptem 7M
126 module.
127 .Pp
128 If
129 .Dv O_NONBLOCK
130 or
131 .Dv O_NDELAY
132 is set on the manager side:
133 .Bl -bullet
134 .It
135 Read on the manager side returns
136 .Sy -1
137 with
138 .Va errno
139 set to
140 .Er EAGAIN
141 if no data is available
142 .It
143 Write returns
144 .Sy -1
145 with
146 .Va errno
147 set to
148 .Er EAGAIN
149 if there is internal flow control
150 .El
151 .Pp
152 Standard STREAMS system calls can access pseudo-terminal devices.
153 The subsidiary devices support the
154 .Dv O_NDELAY
155 and
156 .Dv O_NONBLOCK
157 flags.
158 .Sh XPG4v2 MODE
159 .Em XPG4v2
160 requires that subsidiary pseudo-terminal devices provide the process with an
161 interface that is identical to the terminal interface, without needing to
162 explicitly push any modules to achieve this.
163 It also requires that 0-length messages written on the subsidiary device will
164 be propagated to the manager device.
165 .Pp
166 Experience has shown that most software does not expect subsidiary
167 pseudo-terminal devices to operate in this manner.
168 This XPG4v2-compliant behaviour is only enabled in XPG4v2/SUS
169 .Po
170 see
171 .Xr standards 5
172 .Pc
173 mode.
174 .Sh IOCTLS
175 The manager driver provides several ioctls to support the
176 .Xr grantpt 3C ,
177 .Xr unlockpt 3C ,
178 and
179 .Xr ptsname 3C
180 functions:
181 .Bl -tag -width Ds
182 .It Dv ISPTM
183 Determines whether the file descriptor is that of an open manager device.
184 On success, it returns the value
185 .Sy 0 .
186 .It Dv UNLKPT
187 Unlocks the manager and subsidiary devices.
188 It returns
189 .Sy 0
190 on success.
191 On failure,
192 .Vt errno
193 is set to
194 .Vt EINVAL
195 indicating that the manager device is not open.
196 .El
197 .Sh FILES
198 .Bl -tag -width Pa
199 .It Pa /dev/ptmx
200 Pseudo-terminal manager clone device.
201 .It Pa /dev/pts/N
202 Pseudo-terminal subsidiary devices, where
203 .Sy N
204 is a non-negative integer.
205 Located via calls to
206 .Xr ptsname 3C .
207 .El
208 .Sh EXAMPLES
209 .Sy Example 1
210 Opening the manager and subsidiary device for a pseudo-terminal.
211 .Bd -literal -offset Ds
212 #include <stdlib.h>
213 #include <sys/types.h>
214 #include <sys/stat.h>
215 #include <unistd.h>
216 #include <stropts.h>
217 #include <fcntl.h>
218 #include <err.h>
219 \&...
220 int fdm, fds;
221 char *subsidiaryname;
222 \&...
223 /*
224 * NOTE: Portable applications should use posix_openpt(3C) here:
225 */
226 if ((fdm = open("/dev/ptmx", O_RDWR | O_NOCTTY)) < 0) {
227 err(1, "open manager");
228 }
229 if (grantpt(fdm) != 0 || unlockpt(fdm) != 0 ||
230 (subsidiaryname = ptsname(fdm)) == NULL) {
231 close(fdm);
232 err(1, "locate subsidiary");
233 }
234 if ((fds = open(subsidiaryname, O_RDWR | O_NOCTTY)) < 0) {
235 close(fdm);
236 err(1, "open subsidiary");
237 }
238 if (ioctl(fds, I_PUSH, "ptem") != 0 ||
239 ioctl(fds, I_PUSH, "ldterm") != 0) {
240 close(fds);
241 close(fdm);
242 err(1, "push modules");
243 }
244 .Ed
245 .Sh SEE ALSO
246 .Xr close 2 ,
247 .Xr getmsg 2 ,
248 .Xr open 2 ,
249 .Xr read 2 ,
250 .Xr grantpt 3C ,
251 .Xr posix_openpt 3C ,
252 .Xr ptsname 3C ,
253 .Xr unlockpt 3C ,
254 .Xr standards 5 ,
255 .Xr ldterm 7M ,
256 .Xr pckt 7M ,
257 .Xr ptem 7M ,
258 .Xr ddi_create_minor_node 9F