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The driver
provides support for a device-pair termed a A pseudo terminal is a pair
of character devices, a device and a device. The slave device provides
to a process an interface identical to that described in However, whereas
all other devices which provide the interface described in have a hardware
device of some sort behind them, the slave device has, instead, another
process manipulating it through the master half of the pseudo terminal.
That is, anything written on the master device is given to the slave device
as input and anything written on the slave device is presented as input
on the master device. In configuring, if an optional is given in the specification,
that number of pseudo terminal pairs are configured; the default count
is 32. The following calls apply only to pseudo terminals: Stops output
to a terminal (e.g. like typing Takes no parameter. Restarts output (stopped
by or by typing Takes no parameter. Enable/disable mode. Packet mode
is enabled by specifying (by reference) a nonzero parameter and disabled
by specifying (by reference) a zero parameter. When applied to the master
side of a pseudo terminal, each subsequent from the terminal will return
data written on the slave part of the pseudo terminal preceded by a zero
byte (symbolically defined as or a single byte reflecting control status
information. In the latter case, the byte is an inclusive-or of zero or
more of the bits: whenever the read queue for the terminal is flushed.
whenever the write queue for the terminal is flushed. whenever output
to the terminal is stopped a la whenever output to the terminal is restarted.
whenever is and is whenever the start and stop characters are not
While this mode is in use, the presence of control status information
to be read from the master side may be detected by a for exceptional conditions.
This mode is used by and to implement a remote-echoed, locally flow-controlled
remote login with proper back-flushing of output; it can be used by other
similar programs. Enable/disable a mode that allows a small number of
simple user commands to be passed through the pseudo-terminal, using a
protocol similar to that of The and modes are mutually exclusive. This
mode is enabled from the master side of a pseudo terminal by specifying
(by reference) a nonzero parameter and disabled by specifying (by reference)
a zero parameter. Each subsequent from the master side will return data
written on the slave part of the pseudo terminal preceded by a zero byte,
or a single byte reflecting a user control operation on the slave side.
A user control command consists of a special operation with no data; the
command is given as where is a number in the range 1-255. The operation
value will be received as a single byte on the next from the master side.
The is a no-op that may be used to probe for the existence of this facility.
As with mode, command operations may be detected with a for exceptional
conditions. A mode for the master half of a pseudo terminal, independent
of This mode causes input to the pseudo terminal to be flow controlled
and not input edited (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; a write of 0 bytes is like typing an end-of-file character.
can be used when doing remote line editing in a window manager, or whenever
flow controlled input is required.
master pseudo terminals slave
pseudo terminals
None.
The driver appeared in
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