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+'\" te
+.\" Copyright (c) 1994, Sun Microsystems, Inc.
+.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
+.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
+.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
+.\" Copyright 2022 Oxide Computer Company
+.Dd February 5, 2022
+.Dt PTY 4D
+.Os
+.Sh NAME
+.Nm pty
+.Nd legacy pseudo-terminal driver
+.Sh SYNOPSIS
+.Pa /dev/pty[p-r]*
+.Pp
+.Pa /dev/tty[p-r]*
+.Sh DESCRIPTION
+This driver provides support for legacy static pseudo-terminal devices.
+Modern software does not use this driver, preferring instead the STREAMS-based
+.Xr ptm 4D
+and
+.Xr pts 4D
+pseudo-terminal drivers, consumed through the portable
+.Xr posix_openpt 3C
+interface.
+.Pp
+The
+.Nm pty
+driver provides support for a pair of devices collectively known
+as a
+.Em pseudo-terminal .
+The two devices comprising a pseudo-terminal are known as a
+.Em manager
+and a
+.Em subsidiary .
+The subsidiary device distinguishes between the
+.Dv B0 baud rate and other baud rates specified in
+the
+.Fa c_cflag
+field of the
+.Vt termios
+structure, and the
+.Dv CLOCAL
+flag in that member.
+It does not support any of the other
+.Xr termio 4I
+device control functions specified by flags in the
+.Fa c_cflag
+field of the
+.Vt termios
+structure and by the
+.Dv IGNBRK ,
+.Dv IGNPAR ,
+.Dv PARMRK ,
+or
+.Dv INPCK
+flags in the
+.Fa c_iflag
+field of the
+.Vt termios
+structure, as these functions apply only to asynchronous serial ports.
+All other
+.Xr termio 4I
+functions must be performed by STREAMS modules pushed atop the driver; when a
+subsidiary device is opened, the
+.Xr ldterm 4M
+and
+.Xr ttcompat 4M
+STREAMS modules are automatically pushed on top of the stream, providing the
+standard
+.Xr termio 4I
+interface.
+.Pp
+Instead of having a hardware interface and associated hardware that supports
+the terminal functions, the functions are implemented by another process
+manipulating the manager device of the pseudo-terminal.
+.Pp
+The manager and the subsidiary devices of the pseudo-terminal are tightly
+connected.
+Any data written on the manager device is given to the subsidiary device as
+input, as though it had been received from a hardware interface.
+Any data written on the subsidiary terminal can be read from the manager device
+.Pq "rather than being transmitted from a UAR" .
+.Pp
+The driver is statically configured to provide 48 pseudo-terminal pairs.
+Software that requires dynamic pseudo-terminal devices, or a greater number
+of devices, must be converted to use
+.Xr ptm 4D .
+.Sh IOCTLS
+The standard set of
+.Xr termio 4I
+ioctls are supported by the subsidiary device.
+None of the bits in the
+.Fa c_cflag
+field have any effect on the pseudo-terminal, except that if the baud rate is
+set to
+.Dv B0 ,
+it will appear to the process on the manager device as if the last process on
+the subsidiary device had closed the line; thus, setting the baud rate to
+.Dv B0
+has the effect of
+.Dq hanging up
+the pseudo-terminal, just as it has the effect of
+.Dq hanging up
+a real terminal.
+.Pp
+There is no notion of
+.Dq parity
+on a pseudo-terminal, so none of the flags in the
+.Fa c_iflag
+field that control the processing of parity errors have any
+effect.
+Similarly, there is no notion of a
+.Fa break ,
+so none of the flags that control the processing of breaks, and none of the
+ioctls that generate breaks, have any effect.
+.Pp
+Input flow control is automatically performed; a process that attempts to write
+to the manager device will be blocked if too much unconsumed data is buffered
+on the subsidiary device.
+The input flow control provided by the
+.Dv IXOFF
+flag in the
+.Fa c_iflag
+field is not supported.
+.Pp
+The delays specified in the
+.Fa c_oflag
+field are not supported.
+.Pp
+As there are no modems involved in a pseudo-terminal, the ioctls that return or
+alter the state of modem control lines are silently ignored.
+.Pp
+A few special ioctls are provided on the manager devices of pseudo-terminals to
+provide the functionality needed by applications programs to emulate real
+hardware interfaces:
+.Bl -tag -width Ds
+.It Dv TIOCSTOP
+The argument is ignored.
+Output to the pseudo-terminal is suspended, as if a
+.Sy STOP
+character had been typed.
+.It Dv TIOCSTART
+The argument is ignored.
+Output to the pseudo-terminal is restarted, as if a
+.Sy START
+character had been typed.
+.It Dv TIOCPKT
+The argument is a pointer to an
+.Vt int .
+If the value of the
+.Vt int
+is non-zero,
+.Em packet
+mode is enabled; if the value of the
+.Vt int
+is zero, packet mode is disabled.
+When a pseudo-terminal is in packet mode, each subsequent
+.Xr read 2
+from the manager device will return data written on the subsidiary device
+preceded by a zero byte
+.Po
+symbolically defined as
+.Dv TIOCPKT_DATA
+.Pc ,
+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:
+.Bl -tag -width Ds
+.It Dv TIOCPKT_FLUSHREAD
+Whenever the read queue for the terminal is flushed.
+.It Dv TIOCPKT_FLUSHWRITE
+Whenever the write queue for the terminal is flushed.
+.It Dv TIOCPKT_STOP
+Whenever output to the terminal is stopped using
+.Sy ^S .
+.It Dv TIOCPKT_START
+Whenever output to the terminal is restarted.
+.It Dv TIOCPKT_DOSTOP
+Whenever
+.Em XON/XOFF
+flow control is enabled after being disabled; it is
+considered
+.Dq enabled
+when the
+.Dv IXON
+flag in the
+.Fa c_iflag
+field is set, the
+.Dv VSTOP
+member of the
+.Fa c_cc
+array is
+.Sy ^S
+and the
+.Dv VSTART
+member of the
+.Fa c_cc
+array is
+.Sy ^Q.
+.It Dv TIOCPKT_NOSTOP
+Whenever
+.Em XON/XOFF
+flow control is disabled after being enabled.
+.El
+.It Dv TIOCREMOTE
+The argument is a pointer to an
+.Vt int .
+If the value of the
+.Vt int
+is non-zero,
+.Em remote
+mode is enabled; if the value of the
+.Vt int
+is zero, remote mode is disabled.
+This mode can be enabled or disabled independently of packet mode.
+When a pseudo-terminal is in remote mode, input to the subsidiary device of the
+pseudo-terminal is flow controlled and not input edited (regardless of the mode
+the subsidiary side of the pseudo-terminal).
+.Pp
+Each write to the manager device produces a record boundary for the process
+reading the subsidiary device.
+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
+.Sy EOF
+character.
+Note: this means that a process writing to a pseudo-terminal manager in remote
+mode must keep track of line boundaries, and write only one line at a time to
+the manager.
+.Pp
+If, for example, it were to buffer up several newline characters and write them
+to the manager with one
+.Xr write 2 ,
+it would appear to a process reading from the subsidiary as if a single line
+containing several newline characters had been typed
+.Po
+as if, for example, a user had typed the literal next
+.Pq Sy LNEXT
+character before typing all but the last of those newline characters
+.Pc .
+Remote mode can be used when doing remote line editing in a window manager, or
+whenever flow controlled input is required.
+.El
+.Sh FILES
+.Bl -tag -width Pa
+.It Pa /dev/pty[p-r][0-9a-f]
+Pseudo-terminal manager devices.
+.It Pa /dev/tty[p-r][0-9a-f]
+Pseudo-terminal subsidiary devices.
+.El
+.Sh SEE ALSO
+.Xr rlogin 1 ,
+.Xr posix_openpty 3C ,
+.Xr ptm 4D ,
+.Xr termio 4I ,
+.Xr ldterm 4M ,
+.Xr ttcompat 4M ,
+.Xr rlogind 8
+.Sh NOTES
+This is a legacy device and should not be used by new software.
+.Pp
+It is apparently not possible to send an
+.Sy EOT
+by writing zero bytes in
+.Dv TIOCREMOTE
+mode.