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Files Reference
Provides the pseudo-terminal (pty)
device driver.
The pty device driver
provides support for a pseudo-terminal. A pseudo-terminal
includes a pair of control and slave character
devices. The slave device provides processes with essentially the same
interface as that provided by the tty device driver.
However, instead of providing support for a hardware device, the slave device
is manipulated by another process through the control half of the
pseudo-terminal. That is, anything written on the control device is
given to the slave device as input and anything written on the slave device is
presented as input on the control device.
In AIX Version 4, the pty
subsystem uses naming conventions similar to those from UNIX System V.
There is one node for the control driver, /dev/ptc, and a maximum
number of N nodes for the slave drivers,
/dev/pts/n. N is configurable at pty
configuration and may be changed dynamically by pty reconfiguration, without
closing the opened devices.
The control device is set up as a
clone device whose major device number is the clone device's
major number and whose minor device number is the control driver's major
number. There is no node in the filesystem for control devices.
A control device can be opened only once, but slave devices can be opened
several times.
By opening the control device with
the /dev/ptc special file, an application can quickly open the
control and slave sides of an unused pseudo-terminal. The name of the
corresponding slave side can be retrieved using the ttyname subroutine, which always returns the
name of the slave side.
The following ioctl commands apply
to pseudo-terminals:
| TIOCSTOP
| Stops output to a terminal. This is the same as using the Ctrl-S
key sequence. No parameters are allowed for this command.
|
| TIOCSTART
| Restarts output that was stopped by a TIOCSTOP command or by
the Ctrl-S key sequence. This is the same as typing the Ctrl-Q key
sequence. No parameters are allowed for this command.
|
| TIOCPKT
| Enables and disables the packet mode. Packet mode is enabled by
specifying (by reference) a nonzero parameter. It is disabled by
specifying (by reference) a zero parameter. When applied to the control
side of a pseudo-terminal, each subsequent read from the terminal returns data
written on the slave part of the pseudo terminal. The data is preceded
either by a zero byte (symbolically defined as TIOCPKT_DATA) or by
a single byte that reflects control-status information. In the latter
case, the byte is an inclusive OR of zero or more of the following bits:
- TIOCPKT_FLUSHREAD
- The read queue for the terminal is flushed.
- TIOCPKT_FLUSHWRITE
- The write queue for the terminal is flushed.
- TIOCPKT_STOP
- Output to the terminal is stopped with Ctrl-S.
- TIOCPKT_START
- Output to the terminal is restarted.
- TIOCPKT_DOSTOP
- The stop character defined by the current tty line discipline is
Ctrl-S; the start character defined by the line discipline is
Ctrl-Q.
- TIOCPKT_NOSTOP
- The start and stop characters are not Ctrl-S and Ctrl-Q.
While this mode is in use, the
presence of control-status information to be read from the control side can be
detected by a select for exceptional conditions.
This mode is used by the
rlogin and rlogind commands to log in to a remote host
and implement remote echoing and local Ctrl-S and Ctrl-Q flow control with
proper back-flushing of output.
|
| TIOCUCNTL
| Enables and disables a mode that allows a small number of simple user
ioctl commands to be passed through the pseudo-terminal, using a
protocol similar to that of the TIOCPKT mode. The
TIOCUCNTL and TIOCPKT modes are mutually
exclusive.
This mode is enabled from the
control side of a pseudo-terminal by specifying (by reference) a nonzero
parameter. It is disabled by specifying (by reference) a zero
parameter. Each subsequent read from the control side will return data
written on the slave part of the pseudo-terminal, preceded either by a zero
byte or by a single byte that reflects a user control operation on the slave
side.
A user-control command consists of
a special ioctl operation with no data. That command is issued as
UIOCCMD(Value), where the Value
parameter specifies a number in the range 1 through 255. The operation
value is received as a single byte on the next read from the control
side.
A value of 0 can be used with the
UIOCCMD ioctl operation to probe for the existence of this
facility. The zero is not made available for reading by the control
side. Command operations can be detected with a select for exceptional
conditions.
|
| TIOCREMOTE
| A mode for the control half of a pseudo-terminal, independent of
TIOCPKT. This mode implements flow control, rather than input
editing, for input to the pseudo-terminal, regardless of the terminal
mode. Each write to the control terminal produces a record boundary for
the process reading the terminal. In normal usage, a write of data is
like the data typed as a line on the terminal, while a write of zero bytes is
like typing an end-of-file character. This mode is used for remote line
editing in a window-manager and flow-controlled input.
|
This file is part of Base
Operating System (BOS) Runtime.
With Berkeley pty subsystems,
commands have to search for an unused pseudo-terminal by opening each control
side sequentially. The control side could not be opened if it was
already in use. Thus, the opens would fail, setting the
errno variable to EIO, until an unused pseudo-terminal
was found. It is possible to configure the pty subsystem in order to
use special files with the BSD pty naming convention:
| Control devices
| /dev/pty[p-zA-Z][0-f]
|
| Slave devices
| /dev/tty[p-zA-Z][0-f]
|
These special files are not
symbolic links to the operating system special files. They are
completely separate. The number of control and slave pair devices using
the BSD naming convention is configurable.
The rlogin command, rlogind command.
The ioctl subroutine, ttyname subroutine.
The Special Files Overview.
tty Subsystem
Overview in AIX 5L Version 5.1 General Programming
Concepts: Writing and Debugging Programs.
Understanding
TTY Drivers in AIX 5L Version 5.1 General Programming
Concepts: Writing and Debugging Programs.
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