The pty(4) driver provides support for a device-pair
termed a pseudo terminal. A pseudo terminal is a pair of
character devices, a master device and a subordinate
(slave) device. The subordinate device provides to a process
an interface identical to that described in tty(4). Where all other devices
that provide the interface described in tty(4) have a
hardware device of some sort behind them, the subordinate device
has, another process instead that manipulates it through the master
half of the pseudo terminal. That is, anything written on the
master device is given to the subordinate device as input and
anything written on the subordinate device is presented as input on
the master device.
INTERIX is configured with 256 pseudo terminals.
The quick way to open a master pseudo terminal is to use
open(2) with a path of /dev/ptmx. The name
of the subordinate side can found with ptsname(2).
The following ioctl(2) calls apply only to pseudo
terminals:
TIOCSTOP
Stops output to a terminal (like typing ^S). Takes no
parameter.
TIOCSTART
Restarts output (stopped by TIOCSTOP or by typing ^S). Takes no
parameter.
TIOCPKT
Enable/disable packet mode. Packet mode is enabled by
specifying (by reference) a nonzero parameter and is disabled by
specifying (by reference) a zero parameter. When applied to the
master side of a pseudo terminal, each subsequent read()
from the terminal will return data written on the subordinate part
of the pseudo terminal preceded by a zero byte (symbolically
defined as TIOCPKT_DATA), 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:
TIOCPKT_FLUSHREAD
Whenever the read queue for the terminal is flushed or
emptied.
TIOCPKT_FLUSHWRITE
Whenever the write queue for the terminal is flushed or
emptied.
TIOCPKT_STOP
Whenever output to the terminal is stopped by using ^S.
TIOCPKT_START
Whenever output to the terminal is restarted.
TIOCPKT_DOSTOP
Whenever c_cc[VSTART] is ^S and c_cc[VSTOP] is
^Q.
TIOCPKT_NOSTOP
Whenever the start and stop characters are not ^S/^Q.
While this mode is in use, the presence of control status
information to be read from the master side can be detected by a
select(2) for exceptional conditions.
TIOCPKT_IOCTL
Whenever one of the members of the termios structure for
the terminal changes. Only the new content of the termios
structure is returned. Other TIOCPKT control information (except
for TIOCPKT_DATA) can be combined using the exclusive-OR operation
with this control bit. A select(2) on the master
side of the terminal will return true for read, in addition to
exception.
While in packet mode, if a read(2) request is for
fewer than sizeof(struct termios) +1 bytes and TIOCPKT_IOCTL
control information is available, the TIOCPKT_IOCTL information
will remain pending until a sufficiently large read(2) request is
performed. All other packet mode control bits will be delivered,
and select(2) will continue to return true for read
and exception until the TIOCPKT_IOCTL information is
retrieved.
TIOCUCNTL
Enable/disable 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 TIOCPKT. The TIOCUCNTL and
TIOCPKT 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
read() from the master side will return data written on the
subordinate part of the pseudo terminal preceded by a zero byte, or
a single byte reflecting a user control operation on the
subordinate side. A user control command consists of a special
ioctl() operation with no data; the command is given as
UIOCCMD where n is a number in the range 1-255. The
operation value n will be received as a single byte on the
next read() from the master side. The ioctl()
UIOCCMD is a no-op that can be used to probe for the
existence of this facility. As with TIOCPKT mode, command
operations can be detected with a select() for exceptional
conditions.
TIOCREMOTE
A mode for the master half of a pseudo terminal, independent of
TIOCPKT. This is not enabled in the current version of
INTERIX. This mode causes input to the pseudo terminal to be
flow controlled and not input edited (regardless of the terminal
mode). Each write operation to the control terminal produces a
record boundary for the process reading the terminal. In normal
usage, a write operation 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. TIOCREMOTE can be used when doing remote line editing in
a window manager, or whenever flow controlled input is
required.