ptm(7d) [opensolaris man page]
ptm(7D) Devices ptm(7D) NAME
ptm - STREAMS pseudo-tty master driver DESCRIPTION
The pseudo-tty subsystem simulates a terminal connection, where the master side represents the terminal and the slave represents the user process's special device end point. In order to use the pseudo-tty subsystem, a node for the master side driver /dev/ptmx and N number of nodes for the slave driver must be installed. See pts(7D). The master device is set up as a cloned device where its major device number is the major for the clone device and its minor device number is the major for the ptm driver. There are no nodes in the file system for mas- ter devices. The master pseudo driver is opened using the open(2) system call with /dev/ptmx as the device parameter. The clone open finds the next available minor device for the ptm major device. A master device is available only if it and its corresponding slave device are not already open. When the master device is opened, the cor- responding slave device is automatically locked out. Only one open is allowed on a master device. Multiple opens are allowed on the slave device. After both the master and slave have been opened, the user has two file descriptors which are the end points of a full duplex con- nection composed of two streams which are automatically connected at the master and slave drivers. The user may then push modules onto either side of the stream pair. The master and slave drivers pass all messages to their adjacent queues. Only the M_FLUSH needs some processing. Because the read queue of one side is connected to the write queue of the other, the FLUSHR flag is changed to the FLUSHW flag and vice versa. When the master device is closed an M_HANGUP message is sent to the slave device which will render the device unusable. The process on the slave side gets the errno EIO when attempting to write on that stream but it will be able to read any data remaining on the stream head read queue. When all the data has been read, read() returns 0 indicating that the stream can no longer be used. On the last close of the slave device, a 0-length message is sent to the master device. When the application on the master side issues a read() or getmsg() and 0 is returned, the user of the master device decides whether to issue a close() that dismantles the pseudo-terminal subsystem. If the master device is not closed, the pseudo-tty subsystem will be available to another user to open the slave device. If O_NONBLOCK or O_NDELAY is set, read on the master side returns -1 with errno set to EAGAIN if no data is available, and write returns -1 with errno set to EAGAIN if there is internal flow control. IOCTLS
The master driver supports the ISPTM and UNLKPT ioctls that are used by the functions grantpt(3C), unlockpt(3C) and ptsname(3C). The ioctl ISPTM determines whether the file descriptor is that of an open master device. On success, it returns the 0. The ioctl UNLKPT unlocks the master and slave devices. It returns 0 on success. On failure, the errno is set to EINVAL indicating that the master device is not open. FILES
/dev/ptmx master clone device /dev/pts/M slave devices (M = 0 -> N-1) SEE ALSO
grantpt(3C), ptsname(3C), unlockpt(3C), pckt(7M), pts(7D) STREAMS Programming Guide SunOS 5.11 5 Feb 1997 ptm(7D)
Check Out this Related Man Page
pts(7) Miscellaneous Information Manual pts(7) NAME
pts - STREAMS slave pty (pseudo-terminal) driver SYNOPSIS
DESCRIPTION
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, with (STREAMS pty emulation module) and (STREAMS line discipline module) pushed on top (not shown for simplicity), pro- vides 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 and N number of slave pty devices must be installed (see ptm(7) for more details on master pty). When the master device is opened, the corresponding slave device is automatically locked out. No user can open that slave device until its permissions are changed (via the function) and the device is unlocked (via the function). The user then call the function to obtain the name of the slave device and invoke the system call to open the slave device. Although only one open is allowed on a master device, multiple opens are allowed on the slave device. After both the master 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 that are automatically con- nected by the master and slave devices when they are opened. The user may then push the desired modules (for example, and on for terminal semantics and on for Packet Mode feature). The master and slave drivers pass all STREAMS messages to their adjacent drivers. Only the message needs some special processing because the read queue of the master is connected to the write queue of the slave and vice versa. For example, the flag is changed to flag and vice versa whenever a message travels across the master-slave link. When the master device is closed, an message is sent to the corre- sponding slave device which will render that slave device unusable. The process on the slave side gets the errno when attempting a system call to the slave device file but it will be able to read any data remaining in the slave stream. Finally, when all the data has been read, the system call will return 0, indicating that the slave can no longer be used. On the last close of the slave device, a zero-length message is sent to the corresponding master device. When the application on the master side issues a read(2) or getmsg(2) system calls, a 0 (zero) is returned. The user of the master device may decide to close the master device file, which dismantles the stream on the master side. If the master device remains opened, the corresponding slave device can be opened and used again by another user. EXAMPLES
The following example shows how a STREAMS pty master and slave devices are typically opened. AUTHOR
was developed by HP and OSF. FILES
Streams pty master clone device Streams pty slave devices (0 <= N < where is a kernel tunable parameter which can be changed via SAM (see sam(1M)). SEE ALSO
insf(1M), sam(1M), getmsg(2), ioctl(2), open(2), read(2), write(2), grantpt(3C), ptsname(3C), unlockpt(3C), ldterm(7), ptem(7), ptm(7), streamio(7), termio(7). pts(7)