1pts(7D) Devices pts(7D)
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6 pts - STREAMS pseudo-tty slave driver
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9 The pseudo-tty subsystem simulates a terminal connection, where the
10 master side represents the terminal and the slave represents the user
11 process's special device end point. In order to use the pseudo-tty sub‐
12 system, a node for the master side driver /dev/ptmx and N nodes for the
13 slave driver (N is determined at installation time) must be installed.
14 The names of the slave devices are /dev/pts/M where M has the values 0
15 through N-1. When the master device is opened, the corresponding slave
16 device is automatically locked out. No user may open that slave device
17 until its permissions are adjusted and the device unlocked by calling
18 functions grantpt(3C) and unlockpt(3C). The user can then invoke the
19 open system call with the name that is returned by the ptsname(3C)
20 function. See the example below.
21 Only one open is allowed on a master device. Multiple opens are allowed
24 on the slave device. After both the master and slave have been opened,
25 the user has two file descriptors which are end points of a full duplex
26 connection composed of two streams automatically connected at the mas‐
27 ter and slave drivers. The user may then push modules onto either side
28 of the stream pair. The user needs to push the ptem(7M) and ldterm(7M)
29 modules onto the slave side of the pseudo-terminal subsystem to get
30 terminal semantics.
31 The master and slave drivers pass all messages to their adjacent
34 queues. Only the M_FLUSH needs some processing. Because the read queue
35 of one side is connected to the write queue of the other, the FLUSHR
36 flag is changed to the FLUSHW flag and vice versa. When the master
37 device is closed an M_HANGUP message is sent to the slave device which
38 will render the device unusable. The process on the slave side gets the
39 errno EIO when attempting to write on that stream but it will be able
40 to read any data remaining on the stream head read queue. When all the
41 data has been read, read returns 0 indicating that the stream can no
42 longer be used. On the last close of the slave device, a 0-length mes‐
43 sage is sent to the master device. When the application on the master
44 side issues a read() or getmsg() and 0 is returned, the user of the
45 master device decides whether to issue a close() that dismantles the
46 pseudo-terminal subsystem. If the master device is not closed, the
47 pseudo-tty subsystem will be available to another user to open the
48 slave device. Since 0-length messages are used to indicate that the
49 process on the slave side has closed and should be interpreted that way
50 by the process on the master side, applications on the slave side
51 should not write 0-length messages. If that occurs, the write returns
52 0, and the 0-length message is discarded by the ptem module.
53 The standard STREAMS system calls can access the pseudo-tty devices.
56 The slave devices support the O_NDELAY and O_NONBLOCK flags.
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59 int fdm fds;
60 char *slavename;
61 extern char *ptsname();
62 fdm = open("/dev/ptmx", O_RDWR); /* open master */
64 grantpt(fdm); /* change permission of slave */
65 unlockpt(fdm); /* unlock slave */
66 slavename = ptsname(fdm); /* get name of slave */
67 fds = open(slavename, O_RDWR); /* open slave */
68 ioctl(fds, I_PUSH, "ptem"); /* push ptem */
69 ioctl(fds, I_PUSH, "ldterm"); /* push ldterm*/
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73 /dev/ptmx master clone device
74 /dev/pts/M slave devices (M = 0 -> N-1)
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80 grantpt(3C), ptsname(3C), unlockpt(3C), ldterm(7M), ptm(7D), ptem(7M)
81 STREAMS Programming Guide
84SunOS 5.11 21 Aug 1992 pts(7D)