Integrate the new MPSAFE TTY layer to the FreeBSD operating system.

The last half year I've been working on a replacement TTY layer for the
FreeBSD kernel. The new TTY layer was designed to improve the following:

- Improved driver model:

  The old TTY layer has a driver model that is not abstract enough to
  make it friendly to use. A good example is the output path, where the
  device drivers directly access the output buffers. This means that an
  in-kernel PPP implementation must always convert network buffers into
  TTY buffers.

  If a PPP implementation would be built on top of the new TTY layer
  (still needs a hooks layer, though), it would allow the PPP
  implementation to directly hand the data to the TTY driver.

- Improved hotplugging:

  With the old TTY layer, it isn't entirely safe to destroy TTY's from
  the system. This implementation has a two-step destructing design,
  where the driver first abandons the TTY. After all threads have left
  the TTY, the TTY layer calls a routine in the driver, which can be
  used to free resources (unit numbers, etc).

  The pts(4) driver also implements this feature, which means
  posix_openpt() will now return PTY's that are created on the fly.

- Improved performance:

  One of the major improvements is the per-TTY mutex, which is expected
  to improve scalability when compared to the old Giant locking.
  Another change is the unbuffered copying to userspace, which is both
  used on TTY device nodes and PTY masters.

Upgrading should be quite straightforward. Unlike previous versions,
existing kernel configuration files do not need to be changed, except
when they reference device drivers that are listed in UPDATING.

Obtained from:		//depot/projects/mpsafetty/...
Approved by:		philip (ex-mentor)
Discussed:		on the lists, at BSDCan, at the DevSummit
Sponsored by:		Snow B.V., the Netherlands
dcons(4) fixed by:	kan

1 files changed, 47 insertions, 200 deletions

diff --git a/share/man/man4/pty.4 b/share/man/man4/pty.4
index 868c710..515f912 100644
--- a/share/man/man4/pty.4
+++ b/share/man/man4/pty.4
@@ -1,5 +1,8 @@
-.\" Copyright (c) 1983, 1991, 1993
-.\"	The Regents of the University of California.  All rights reserved.
+.\" Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Portions of this software were developed under sponsorship from Snow
+.\" B.V., the Netherlands.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
@@ -9,18 +12,11 @@
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
-.\" 3. All advertising materials mentioning features or use of this software
-.\"    must display the following acknowledgement:
-.\"	This product includes software developed by the University of
-.\"	California, Berkeley and its contributors.
-.\" 4. Neither the name of the University nor the names of its contributors
-.\"    may be used to endorse or promote products derived from this software
-.\"    without specific prior written permission.
 .\"
-.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
@@ -29,214 +25,65 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"     @(#)pty.4	8.2 (Berkeley) 11/30/93
 .\" $FreeBSD$
 .\"
-.Dd November 30, 1993
+.Dd August 20, 2008
 .Dt PTY 4
 .Os
 .Sh NAME
 .Nm pty
-.Nd pseudo terminal driver
+.Nd BSD-style compatibility pseudo-terminal driver
 .Sh SYNOPSIS
 .Cd "device pty"
 .Sh DESCRIPTION
 The
 .Nm
-driver provides support for a device-pair termed a
-.Em pseudo terminal .
-A pseudo terminal is a pair of character devices, a
-.Em master
-device and a
-.Em slave
-device.
-The slave device provides to a process an interface identical
-to that described in
-.Xr tty 4 .
-However, whereas all other devices which provide the
-interface described in
-.Xr tty 4
-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.
-.Pp
-The following
-.Xr ioctl 2
-calls apply only to pseudo terminals:
-.Bl -tag -width TIOCREMOTE
-.It Dv TIOCSTOP
-Stops output to a terminal (e.g.\& like typing
-.Ql ^S ) .
-Takes
-no parameter.
-.It Dv TIOCSTART
-Restarts output (stopped by
-.Dv TIOCSTOP
-or by typing
-.Ql ^S ) .
-Takes no parameter.
-.It Dv TIOCPKT
-Enable/disable
-.Em packet
-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
-.Xr read 2
-from the terminal will return data written on the slave part of
-the pseudo terminal preceded by a zero byte (symbolically
-defined as
-.Dv 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:
-.Bl -tag -width TIOCPKT_FLUSHWRITE
-.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 a la
-.Ql ^S .
-.It Dv TIOCPKT_START
-whenever output to the terminal is restarted.
-.It Dv TIOCPKT_DOSTOP
-whenever
-.Em t_stopc
-is
-.Ql ^S
-and
-.Em t_startc
-is
-.Ql ^Q .
-.It Dv TIOCPKT_NOSTOP
-whenever the start and stop characters are not
-.Ql ^S/^Q .
-.El
-.Pp
-While this mode is in use, the presence of control status information
-to be read from the master side may be detected by a
-.Xr select 2
-for exceptional conditions.
-.Pp
-This mode is used by
-.Xr rlogin 1
-and
-.Xr rlogind 8
-to implement a remote-echoed, locally
-.Ql ^S/^Q
-flow-controlled
-remote login with proper back-flushing of output; it can be
-used by other similar programs.
-.It Dv TIOCUCNTL
-Enable/disable a mode that allows a small number of simple user
-.Xr ioctl 2
-commands to be passed through the pseudo-terminal,
-using a protocol similar to that of
-.Dv TIOCPKT .
-The
-.Dv TIOCUCNTL
-and
-.Dv 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
-.Xr read 2
-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
-.Xr ioctl 2
-operation with no data; the command is given as
-.Dv UIOCCMD Ns (n) ,
-where
-.Ar n
-is a number in the range 1-255.
-The operation value
-.Ar n
-will be received as a single byte on the next
-.Xr read 2
-from the master side.
-The
-.Xr ioctl 2
-.Dv UIOCCMD Ns (0)
-is a no-op that may be used to probe for
-the existence of this facility.
-As with
-.Dv TIOCPKT
-mode, command operations may be detected with a
-.Xr select 2
-for exceptional conditions.
-.El
+driver provides support for the traditional BSD naming scheme that was
+used for accessing pseudo-terminals.
+When the device
+.Pa /dev/ptyXX
+is being opened, a new terminal shall be created with the
+.Xr pts 4
+driver.
+A device node for this terminal shall be created, which has the name
+.Pa /dev/ttyXX .
 .Pp
-There is currently two
-.Nm
-systems available: the original
-.Bx Nm ,
-and a
-SysVR4 pts-like implementation.
-It is possible to switch between the two implementations by setting the
-.Va kern.pts.enable
-sysctl.
-Setting it to 0 will use the
-.Bx Nm ,
-to non-zero the pts implementation.
-It defaults to 0.
-It is possible to set the maximum number of ptys
-which can be allocated at the same time with the
-.Va kern.pts.max
-sysctl.
-It defaults to 1000.
-It is not recommended to use more than 1000 pseudo-terminals, as all software
-which use
-.Xr utmp 5
-will not be able to handle pseudo-terminals with number superior to 999.
-.Pp
-The pts implementation also supports the
-.Dv TIOCGPTN
-.Xr ioctl 2
-call, which takes a pointer to an
-.Vt "unsigned int"
-as a parameter and provides the
-number of the pty.
+New code should not try to allocate pseudo-terminals using this
+interface.
+It is only provided for compatibility with older C libraries
+that tried to open such devices when
+.Xr posix_openpt 2
+was being called.
 .Sh FILES
-The files used by the
-.Bx
-pseudo terminals implementation are:
-.Pp
-.Bl -tag -width ".Pa /dev/tty[p-sP-S][0-9a-v]" -compact
-.It Pa /dev/pty[p-sP-S][0-9a-v]
-master pseudo terminals
-.It Pa /dev/tty[p-sP-S][0-9a-v]
-slave pseudo terminals
-.El
+The BSD-style compatibility pseudo-terminal driver uses the following
+device names:
 .Pp
-The files used by the pts implementation are:
-.Pp
-.Bl -tag -width ".Pa /dev/pts/[num]" -compact
-.It Pa /dev/ptmx
-control device, returns a file descriptor to a new master pseudo terminal
-when opened.
-.It Pa /dev/pty[num]
-master pseudo terminals
-.It Pa /dev/pts/[num]
-slave pseudo terminals
+.Bl -tag -width ".Pa /dev/pty[l-sL-S][0-9a-v]"
+.It Pa /dev/pty[l-sL-S][0-9a-v]
+Pseudo-terminal master devices.
+.It Pa /dev/tty[l-sL-S][0-9a-v]
+Pseudo-terminal slave devices.
 .El
 .Sh DIAGNOSTICS
 None.
 .Sh SEE ALSO
+.Xr posix_openpt 2 ,
+.Xr pts 4 ,
 .Xr tty 4
 .Sh HISTORY
+A
+pseudo-terminal driver appeared in
+.Bx 4.2 .
+.Sh BUGS
+Unlike previous implementations, the master slave device nodes are
+destroyed when the PTY becomes unused.
+A call to
+.Xr stat 2
+on a nonexistent master device will already cause a new master device
+node to be created.
+The master device can only be destroyed by opening and closing it.
+.Pp
 The
 .Nm
-driver appeared in
-.Bx 4.2 .
+driver cannot be unloaded, because it cannot determine if it is being
+used.