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 ptm(7)								      ptm(7)

      ptm - STREAMS master pty (pseudo-terminal) driver

      #include <&lt&lt&lt;sys/stropts.h>&gt&gt&gt;
      #include <&lt&lt&lt;sys/ptyio.h>&gt&gt&gt;
      #include <&lt&lt&lt;sys/strtio.h>&gt&gt&gt;

      int open("/dev/ptmx", O_RDWR);

      A pseudo-terminal (pty) consists of a tightly-coupled pair of
      character devices, called the master device and slave device.  The pty
      master and slave device drivers work together to simulate a terminal
      connection where the master provides a connection to the pseudo
      terminal server process and the slave provides a terminal device
      special file access for the terminal application processes, as
      depicted below:

			    | pty functions  |
	   Application <--> |----------------| <--> Server
	    Processes	    | Slave | Master |	     Process
			    | (pts) | (ptm)  |

      The slave driver, pts with ptem (STREAMS pty emulation module) and
      ldterm (STREAMS line discipline module) pushed on top (not shown for
      simplicity), provides a terminal interface as described in termio(7).
      Whereas devices that provide the terminal interface described in
      termio(7) have a hardware device behind them; in contrast, the slave
      device has another process manipulating it through the master side of
      the pty.	Data written on the master device is given to the slave
      device as input and data written on the slave device is presented as
      input on the master device.

      In order to use the STREAMS pty subsystem, a node for the master pty
      driver /dev/ptmx and N number of slave pty devices must be installed
      (see pts(7) for details on slave pty).  There are no nodes in the file
      system for each individual master device.	 Rather, the master driver
      is set up as a STREAMS clone driver (see clone(7)) with its major
      device number set to the major for the clone driver and its minor
      device number set to the major for the ptm driver.  The master driver
      is opened using the open() system call with /dev/ptmx as the device
      file parameter.  The clone open finds the next available minor number
      for the master device.  The master device is available only if it and
      its corresponding slave device are not already opened.  Only one open
      is allowed on a master device whereas multiple open are allowed on the
      slave device.  When the master device is opened, the corresponding
      slave device is automatically locked out (see pts(7) on how to unlock
      the slave and obtain the slave device name).  After both the master

 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000

 ptm(7)								      ptm(7)

      and slave have been opened, the user has two file descriptors which
      represent the end points of a full duplex connection composed of two
      streams.	These two streams are automatically connected by the master
      and slave devices when they are opened.  The user may then push the
      necessary modules on the master and slave streams (e.g., ptem and
      ldterm, on pts for terminal semantics, and pckt on ptm for Packet Mode

      The master and slave drivers pass all STREAMS messages to their
      adjacent drivers.	 Only the M_FLUSH message needs some special
      processing because the read queue of the master is connected to the
      write queue of the slave and vice versa.	Hence, the FLUSHR flag is
      changed to FLUSHW flag and vice versa whenever a M_FLUSH message
      travels across the master-slave link.  When the master device is
      closed, an M_HANGUP message is sent to the corresponding slave device
      which will render that slave device unusable.  The process on the
      slave side gets the errno [ENXIO] when attempting a write() system
      call on the slave device but it will be able to read any data
      remaining on the slave stream.  Finally, when all the data have been
      read, the read() system call will return 0 (zero) indicating that the
      slave can no longer be used.  On the last close of the slave device, a
      zero-length M_DATA message is sent to the corresponding master device.
      When the application on the master side issues a read() or getmsg()
      system calls and a 0 is returned.	 The user of the master device
      decides whether to close the master device file which will dismantle
      the streams on the master side.  If the master device remains opened,
      the corresponding slave device can be opened and used again by another

      Unlike the slave device, the master device does not act like a
      terminal.	 If O_NDELAY or O_NONBLOCK is set, a read on the master
      device returns -1 with errno set to [EAGAIN] if no data is available,
      and a write returns -1 with errno set to [EAGAIN] if there is internal
      flow control on the stream.

      The master ptm driver supports the following ioctl() requests:

      ISPTM	     Determines whether the file descriptor is that of an
		     open master device.  On success, it returns the major
		     and minor number (type dev_t) of the master device
		     which can be used to determine the name of the
		     corresponding slave device.  On failure, it returns -1
		     with errno set to [EINVAL].  ISPTM on HP-UX can return
		     valid device number with negative value.  For example,
		     with major number of the STREAMS pty master being 0x9c,
		     ICPTM will return 0x9C000000 which is a negative
		     number.  Therefore, it is imperative that applications
		     check for an explicit -1 instead of "< 0" (less than 0)
		     on the return value.

 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000

 ptm(7)								      ptm(7)

		     ISPTM is used by functions grantpt(), unlockpt(), and
		     ptsname().	 User applications normally do not need to
		     invoke this ioctl.	 The format of this ioctl is:

			  int ioctl(master_fd, ISPTM, 0)

      UNLKPT	     Unlocks the master and the corresponding slave devices.
		     On success, it returns 0.	On failure, it returns -1
		     with errno set to [EINVAL].  UNLKPT is used by function
		     unlockpt().  User applications normally do not need to
		     invoke this ioctl.	 The format of this ioctl is:

			  int ioctl(master_fd, UNLKPT, 0)

      TIOCREMOTE     This ioctl puts the STREAMS pty in and out of Remote
		     Mode.  When Remote Mode is on, input data will be
		     flow-controlled and passed through ldterm without any
		     input processing regardless of the terminal mode.	When
		     the pty master driver receives this ioctl, it will send
		     an M_CTL message downstream to ldterm via ptm, pts, and
		     ptem.  The command in the M_CTL message is set to
		     MC_NO_CANON or MC_DO_CANON depending whether to turn on
		     or off the Remote Mode.  The format of this ioctl is:

			  int ioctl(master_fd, TIOCREMOTE, argument)

		     where the argument is set to 1 to turn on Remote Mode
		     and 0 to turn it off.  Remote Mode is normally used
		     when doing remote line editing in a window manager, or
		     whenever flow-controlled input is required.  Each write
		     to the master device produces a record boundary for the
		     process reading the slave devices.	 In normal usage, a
		     write of data is like the data typed as a line on the
		     terminal; a write of 0 (zero) bytes is like typing an
		     EOF (End-of-File) character.

      TIOCSIGNAL     This ioctl allows the master process to send a signal
		     to the slave process.  The format of this ioctl is:

			  int ioctl(master_fd, TIOCSIGNAL, argument)

		     where the argument is the signal number as defined in
		     the header file <&lt&lt&lt;sys/signal.h>&gt&gt&gt;.  For example the master
		     process can send an SIGINT signal to the slave process
		     by doing:

			  ioctl(master_fd, TIOCSIGNAL, SIGINT)

      ptm was developed by HP and OSF.

 Hewlett-Packard Company	    - 3 -   HP-UX Release 11i: November 2000

 ptm(7)								      ptm(7)

      /dev/ptmx		Streams pty master clone device
      /dev/pts/N	Streams pty slave devices (0 <= N < NSTRPTY), where
			NSTRPTY is a kernel tunable parameter which can be
			changed via SAM.

      insf(1M), getmsg(2), ioctl(2), open(2), read(2), write(2),
      grantpt(3C), ptsname(3C), unlockpt(3C), clone(7), ldterm(7), pckt(7),
      ptem(7), pts(7), streamio(7), termio(7).

 Hewlett-Packard Company	    - 4 -   HP-UX Release 11i: November 2000