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   7 .TH PTM 7D "Feb 5, 1997"
   8 .SH NAME
   9 ptm \- STREAMS pseudo-tty master driver
  10 .SH DESCRIPTION
  11 .sp
  12 .LP
  13 The pseudo-tty subsystem simulates a terminal connection, where the master side
  14 represents the terminal and the slave represents the user process's special
  15 device end point. In order to use the pseudo-tty subsystem, a node for the
  16 master side driver \fB/dev/ptmx\fR and \fBN\fR number of nodes for the slave
  17 driver must be installed. See \fBpts\fR(7D). The master device is set up as a
  18 cloned device where its major device number is the major for the clone device
  19 and its minor device number is the major for the \fBptm\fR driver. There are no
  20 nodes in the file system for master devices. The master pseudo driver is opened
  21 using the \fBopen\fR(2) system call with \fB/dev/ptmx\fR as the device
  22 parameter. The clone open finds the next available minor device for the
  23 \fBptm\fR major device.
  24 .sp
  25 .LP
  26 A master device is available only if it and its corresponding slave device are
  27 not already open. When the master device is opened, the corresponding slave
  28 device is automatically locked out. Only one open is allowed on a master
  29 device.  Multiple opens are allowed on the slave device. After both the master
  30 and slave have been opened, the user has two file descriptors which are the end
  31 points of a full duplex connection composed of two streams which are
  32 automatically connected at the master and slave drivers. The user may then push
  33 modules onto either side of the stream pair.
  34 .sp
  35 .LP
  36 The master and slave drivers pass all messages to their adjacent queues. Only
  37 the \fBM_FLUSH\fR needs some processing. Because the read queue of one side is
  38 connected to the write queue of the other, the \fBFLUSHR\fR flag is changed to
  39 the \fBFLUSHW\fR flag and vice versa. When the master device is closed an
  40 \fBM_HANGUP\fR message is sent to the slave device which will render the device
  41 unusable. The process on the slave side gets the errno \fBEIO\fR when
  42 attempting to write on that stream but it will be able to read any data
  43 remaining on the stream head read queue. When all the data has been read,
  44 \fBread()\fR returns 0 indicating that the stream can no longer be used. On the
  45 last close of the slave device, a 0-length message is sent to the master
  46 device. When the application on the master side issues a \fBread()\fR or
  47 \fBgetmsg()\fR and 0 is returned, the user of the master device decides whether
  48 to issue a \fBclose()\fR that dismantles the pseudo-terminal subsystem. If the
  49 master device is not closed, the pseudo-tty subsystem will be available to
  50 another user to open the slave device.
  51 .sp
  52 .LP
  53 If \fBO_NONBLOCK\fR or \fBO_NDELAY\fR is set, read on the master side returns
  54 \(mi1 with errno set to \fBEAGAIN\fR if no data is available, and write returns
  55 \(mi1 with errno set to \fBEAGAIN\fR if there is internal flow control.
  56 .SH IOCTLS
  57 .sp
  58 .LP
  59 The master driver supports the \fBISPTM\fR and \fBUNLKPT\fR ioctls that are
  60 used by the functions \fBgrantpt\fR(3C), \fBunlockpt\fR(3C) and
  61 \fBptsname\fR(3C). The ioctl \fBISPTM\fR determines whether the file descriptor
  62 is that of an open master device. On success, it returns the 0. The ioctl
  63 \fBUNLKPT\fR unlocks the master and slave devices. It returns 0 on success. On
  64 failure, the errno is set to \fBEINVAL\fR indicating that the master device is
  65 not open.
  66 .SH FILES
  67 .sp
  68 .ne 2
  69 .na
  70 \fB\fB/dev/ptmx\fR\fR
  71 .ad
  72 .RS 14n
  73 master clone device
  74 .RE
  75 
  76 .sp
  77 .ne 2
  78 .na
  79 \fB\fB/dev/pts/M\fR\fR
  80 .ad
  81 .RS 14n
  82 slave devices (M = 0 -> N-1)
  83 .RE
  84 
  85 .SH SEE ALSO
  86 .sp
  87 .LP
  88 \fBgrantpt\fR(3C), \fBptsname\fR(3C), \fBunlockpt\fR(3C), \fBpckt\fR(7M),
  89 \fBpts\fR(7D)
  90 .sp
  91 .LP
  92 \fISTREAMS Programming Guide\fR