1ptm(7D) Devices ptm(7D)
2
6 ptm - STREAMS pseudo-tty master driver
7
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 number of
13 nodes for the slave driver must be installed. See pts(7D). The master
14 device is set up as a cloned device where its major device number is
15 the major for the clone device and its minor device number is the major
16 for the ptm driver. There are no nodes in the file system for master
17 devices. The master pseudo driver is opened using the open(2) system
18 call with /dev/ptmx as the device parameter. The clone open finds the
19 next available minor device for the ptm major device.
20 A master device is available only if it and its corresponding slave
23 device are not already open. When the master device is opened, the cor‐
24 responding slave device is automatically locked out. Only one open is
25 allowed on a master device. Multiple opens are allowed on the slave
26 device. After both the master and slave have been opened, the user has
27 two file descriptors which are the end points of a full duplex connec‐
28 tion composed of two streams which are automatically connected at the
29 master and slave drivers. The user may then push modules onto either
30 side of the stream pair.
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.
49 If O_NONBLOCK or O_NDELAY is set, read on the master side returns −1
52 with errno set to EAGAIN if no data is available, and write returns −1
53 with errno set to EAGAIN if there is internal flow control.
54
56 The master driver supports the ISPTM and UNLKPT ioctls that are used by
57 the functions grantpt(3C), unlockpt(3C) and ptsname(3C). The ioctl
58 ISPTM determines whether the file descriptor is that of an open master
59 device. On success, it returns the 0. The ioctl UNLKPT unlocks the mas‐
60 ter and slave devices. It returns 0 on success. On failure, the errno
61 is set to EINVAL indicating that the master device is not open.
62
64 /dev/ptmx master clone device
65 /dev/pts/M slave devices (M = 0 -> N-1)
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71 grantpt(3C), ptsname(3C), unlockpt(3C), pckt(7M), pts(7D)
72 STREAMS Programming Guide
75SunOS 5.11 5 Feb 1997 ptm(7D)