f64342e354
drain timeout handling to historical freebsd behavior. The primary reason for these changes is the need to have tty_drain() call ttydevsw_busy() at some reasonable sub-second rate, to poll hardware that doesn't signal an interrupt when the transmit shift register becomes empty (which includes virtually all USB serial hardware). Such hardware hangs in a ttyout wait, because it never gets an opportunity to trigger a wakeup from the sleep in tty_drain() by calling ttydisc_getc() again, after handing the last of the buffered data to the hardware. While researching the history of changes to tty_drain() I stumbled across some email describing the historical BSD behavior of tcdrain() and close() on serial ports, and the ability of comcontrol(1) to control timeout behavior. Using that and some advice from Bruce Evans as a guide, I've put together these changes to implement the hardware polling and restore the historical timeout behaviors... - tty_drain() now calls ttydevsw_busy() in a loop at 10 Hz to accomodate hardware that requires polling for busy state. - The "new historical" behavior for draining during close(2) is retained: the drain timeout is "1 second without making any progress". When the 1-second timeout expires, if the count of bytes remaining in the tty layer buffer is smaller than last time, the timeout is extended for another second. Unfortunately, the same logic cannot be extended all the way down to the hardware, because the interface to that layer is a simple busy/not-busy indication. - Due to the previous point, an application that needs a guarantee that all data has been transmitted must use TIOCDRAIN/tcdrain(3) before calling close(2). - The historical behavior of honoring the drainwait setting for TIOCDRAIN (used by tcdrain(3)) is restored. - The historical kern.drainwait sysctl to control the global default drainwait time is restored, but is now named kern.tty_drainwait. - The historical default drainwait timeout of 300 seconds is restored. - Handling of TIOCGDRAINWAIT and TIOCSDRAINWAIT ioctls is restored (this also makes the comcontrol(1) drainwait verb work again). - Manpages are updated to document these behaviors. Reviewed by: bde (prior version)
376 lines
12 KiB
Groff
376 lines
12 KiB
Groff
.\" Copyright (c) 1991, 1992, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tty.4 8.3 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd January 11, 2017
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.Dt TTY 4
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.Os
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.Sh NAME
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.Nm tty
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.Nd general terminal interface
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.Sh SYNOPSIS
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.In sys/ioctl.h
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.Sh DESCRIPTION
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This section describes the interface to the terminal drivers
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in the system.
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.Ss Terminal Special Files
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Each hardware terminal port on the system usually has a terminal special device
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file associated with it in the directory ``/dev/'' (for
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example, ``/dev/tty03'').
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When a user logs into
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the system on one of these hardware terminal ports, the system has already
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opened the associated device and prepared the line for normal interactive
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use (see
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.Xr getty 8 . )
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There is also a special case of a terminal file that connects not to
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a hardware terminal port, but to another program on the other side.
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These special terminal devices are called
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.Em ptys
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and provide the mechanism necessary to give users the same interface to the
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system when logging in over a network (using
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.Xr rlogin 1 ,
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or
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.Xr telnet 1
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for example).
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Even in these cases the details of how the terminal
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file was opened and set up is already handled by special software
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in the system.
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Thus, users do not normally need to worry about the details of
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how these lines are opened or used.
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Also, these lines are often used
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for dialing out of a system (through an out-calling modem), but again
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the system provides programs that hide the details of accessing
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these terminal special files (see
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.Xr tip 1 ) .
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.Pp
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When an interactive user logs in, the system prepares the line to
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behave in a certain way (called a
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.Em "line discipline" ) ,
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the particular details of which is described in
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.Xr stty 1
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at the command level, and in
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.Xr termios 4
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at the programming level.
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A user may be concerned with changing
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settings associated with his particular login terminal and should refer
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to the preceding man pages for the common cases.
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The remainder of this man page is concerned
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with describing details of using and controlling terminal devices
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at a low level, such as that possibly required by a program wishing
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to provide features similar to those provided by the system.
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.Ss Terminal File Operations
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All of the following operations are invoked using the
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.Xr ioctl 2
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system call.
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Refer to that man page for a description of the
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.Em request
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and
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.Em argp
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parameters.
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In addition to the ioctl
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.Em requests
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defined here, the specific line discipline
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in effect will define other
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.Em requests
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specific to it (actually
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.Xr termios 4
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defines them as function calls, not ioctl
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.Em requests . )
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The following section lists the available ioctl requests.
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The name of the request, a description of its purpose, and the typed
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.Em argp
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parameter (if any)
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are listed.
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For example, the first entry says
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.Pp
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.D1 Em "TIOCSPGRP int *tpgrp"
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.Pp
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and would be called on the terminal associated with
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file descriptor zero by the following code fragment:
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.Bd -literal
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int pgrp;
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pgrp = getpgrp();
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ioctl(0, TIOCSPGRP, &pgrp);
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.Ed
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.Ss Terminal File Request Descriptions
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.Bl -tag -width TIOCGWINSZ
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.It Dv TIOCSETD Fa int *ldisc
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This call is obsolete but left for compatibility.
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Before
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.Fx 8.0 ,
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it would change to the new line discipline pointed to by
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.Fa ldisc .
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.It Dv TIOCGETD Fa int *ldisc
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Return the current line discipline in the integer pointed to by
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.Fa ldisc .
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.It Dv TIOCSBRK Fa void
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Set the terminal hardware into BREAK condition.
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.It Dv TIOCCBRK Fa void
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Clear the terminal hardware BREAK condition.
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.It Dv TIOCSDTR Fa void
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Assert data terminal ready (DTR).
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.It Dv TIOCCDTR Fa void
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Clear data terminal ready (DTR).
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.It Dv TIOCGPGRP Fa int *tpgrp
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Return the current process group with which the terminal is associated
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in the integer pointed to by
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.Fa tpgrp .
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcgetattr
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call.
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.It Dv TIOCSPGRP Fa int *tpgrp
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Associate the terminal with the process group (as an integer) pointed to by
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.Fa tpgrp .
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcsetattr
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call.
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.It Dv TIOCGETA Fa struct termios *term
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Place the current value of the termios state associated with the
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device in the termios structure pointed to by
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.Fa term .
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcgetattr
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call.
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.It Dv TIOCSETA Fa struct termios *term
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Set the termios state associated with the device immediately.
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcsetattr
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call with the
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.Dv TCSANOW
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option.
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.It Dv TIOCSETAW Fa struct termios *term
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First wait for any output to complete, then set the termios state
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associated with the device.
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcsetattr
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call with the
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.Dv TCSADRAIN
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option.
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.It Dv TIOCSETAF Fa struct termios *term
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First wait for any output to complete, clear any pending input,
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then set the termios state associated with the device.
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This is the underlying call that implements the
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.Xr termios 4
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.Fn tcsetattr
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call with the
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.Dv TCSAFLUSH
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option.
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.It Dv TIOCOUTQ Fa int *num
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Place the current number of characters in the output queue in the
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integer pointed to by
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.Fa num .
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.It Dv TIOCSTI Fa char *cp
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Simulate typed input.
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Pretend as if the terminal received the character pointed to by
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.Fa cp .
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.It Dv TIOCNOTTY Fa void
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This call is obsolete but left for compatibility.
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In the past, when a process that did not have a controlling terminal (see
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.Em The Controlling Terminal
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in
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.Xr termios 4 )
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first opened a terminal device, it acquired that terminal as its
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controlling terminal.
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For some programs this was a hazard as they
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did not want a controlling terminal in the first place, and this
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provided a mechanism to disassociate the controlling terminal from
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the calling process.
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It
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.Em must
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be called by opening the file
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.Pa /dev/tty
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and calling
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.Dv TIOCNOTTY
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on that file descriptor.
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.Pp
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The current system does not allocate a controlling terminal to
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a process on an
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.Fn open
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call: there is a specific ioctl called
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.Dv TIOCSCTTY
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to make a terminal the controlling
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terminal.
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In addition, a program can
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.Fn fork
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and call the
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.Fn setsid
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system call which will place the process into its own session - which
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has the effect of disassociating it from the controlling terminal.
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This is the new and preferred method for programs to lose their controlling
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terminal.
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.It Dv TIOCSTOP Fa void
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Stop output on the terminal (like typing ^S at the keyboard).
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.It Dv TIOCSTART Fa void
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Start output on the terminal (like typing ^Q at the keyboard).
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.It Dv TIOCSCTTY Fa void
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Make the terminal the controlling terminal for the process (the process
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must not currently have a controlling terminal).
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.It Dv TIOCDRAIN Fa void
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Wait until all output is drained, or until the drain wait timeout expires.
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.It Dv TIOCGDRAINWAIT Fa int *timeout
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Return the current drain wait timeout in seconds.
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.It Dv TIOCSDRAINWAIT Fa int *timeout
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Set the drain wait timeout in seconds.
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A value of zero disables timeouts.
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The default drain wait timeout is controlled by the tunable
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.Xr sysctl 8
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OID
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.Va kern.tty_drainwait .
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.It Dv TIOCEXCL Fa void
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Set exclusive use on the terminal.
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No further opens are permitted except by root.
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Of course, this means that programs that are run by
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root (or setuid) will not obey the exclusive setting - which limits
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the usefulness of this feature.
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.It Dv TIOCNXCL Fa void
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Clear exclusive use of the terminal.
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Further opens are permitted.
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.It Dv TIOCFLUSH Fa int *what
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If the value of the int pointed to by
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.Fa what
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contains the
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.Dv FREAD
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bit as defined in
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.In sys/file.h ,
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then all characters in the input queue are cleared.
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If it contains the
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.Dv FWRITE
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bit, then all characters in the output queue are cleared.
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If the value of the integer is zero, then it behaves as if both the
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.Dv FREAD
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and
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.Dv FWRITE
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bits were set (i.e., clears both queues).
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.It Dv TIOCGWINSZ Fa struct winsize *ws
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Put the window size information associated with the terminal in the
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.Va winsize
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structure pointed to by
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.Fa ws .
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The window size structure contains the number of rows and columns (and pixels
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if appropriate) of the devices attached to the terminal.
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It is set by user software
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and is the means by which most full\&-screen oriented programs determine the
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screen size.
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The
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.Va winsize
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structure is defined in
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.In sys/ioctl.h .
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.It Dv TIOCSWINSZ Fa struct winsize *ws
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Set the window size associated with the terminal to be the value in
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the
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.Va winsize
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structure pointed to by
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.Fa ws
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(see above).
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.It Dv TIOCCONS Fa int *on
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If
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.Fa on
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points to a non-zero integer, redirect kernel console output (kernel printf's)
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to this terminal.
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If
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.Fa on
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points to a zero integer, redirect kernel console output back to the normal
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console.
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This is usually used on workstations to redirect kernel messages
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to a particular window.
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.It Dv TIOCMSET Fa int *state
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The integer pointed to by
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.Fa state
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contains bits that correspond to modem state.
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Following is a list of defined variables and the modem state they represent:
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.Pp
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.Bl -tag -width TIOCMXCTS -compact
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.It TIOCM_LE
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Line Enable.
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.It TIOCM_DTR
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Data Terminal Ready.
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.It TIOCM_RTS
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Request To Send.
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.It TIOCM_ST
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Secondary Transmit.
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.It TIOCM_SR
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Secondary Receive.
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.It TIOCM_CTS
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Clear To Send.
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.It TIOCM_CAR
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Carrier Detect.
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.It TIOCM_CD
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Carrier Detect (synonym).
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.It TIOCM_RNG
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Ring Indication.
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.It TIOCM_RI
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Ring Indication (synonym).
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.It TIOCM_DSR
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Data Set Ready.
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.El
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.Pp
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This call sets the terminal modem state to that represented by
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.Fa state .
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Not all terminals may support this.
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.It Dv TIOCMGET Fa int *state
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Return the current state of the terminal modem lines as represented
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above in the integer pointed to by
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.Fa state .
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.It Dv TIOCMBIS Fa int *state
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The bits in the integer pointed to by
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.Fa state
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represent modem state as described above, however the state is OR-ed
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in with the current state.
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.It Dv TIOCMBIC Fa int *state
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The bits in the integer pointed to by
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.Fa state
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represent modem state as described above, however each bit which is on
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in
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.Fa state
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is cleared in the terminal.
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.El
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.Sh IMPLEMENTATION NOTES
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The total number of input and output bytes
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through all terminal devices
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are available via the
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.Va kern.tk_nin
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and
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.Va kern.tk_nout
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read-only
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.Xr sysctl 8
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variables.
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.Sh SEE ALSO
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.Xr stty 1 ,
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.Xr ioctl 2 ,
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.Xr ng_tty 4 ,
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.Xr pty 4 ,
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.Xr termios 4 ,
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.Xr getty 8
|