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, 181 insertions, 0 deletions

diff --git a/share/man/man4/pts.4 b/share/man/man4/pts.4
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+.\" Copyright (c) 1983, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
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+.\" modification, are permitted provided that the following conditions
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+.\"	This product includes software developed by the University of
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+.\" 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.
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+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)pty.4	8.2 (Berkeley) 11/30/93
+.\" $FreeBSD$
+.\"
+.Dd August 20, 2008
+.Dt PTS 4
+.Os
+.Sh NAME
+.Nm pts
+.Nd pseudo-terminal driver
+.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 TIOCPTMASTER
+.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
+.Dv VSTOP
+is
+.Ql ^S
+and
+.Dv VSTART
+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 TIOCGPTN
+Obtain device unit number, which can be used to generate the filename of
+the pseudo-terminal slave device. This
+.Xr ioctl 2
+should not be used directly. Instead, the
+.Xr ptsname 3
+function should be used.
+.It Dv TIOCPTMASTER
+Determine whether the file descriptor is pointing to a pseudo-terminal
+master device.
+This 
+.Xr ioctl 2
+should not be used directly. It is used to implement routines like
+.Xr grantpt 3 .
+.El
+.Pp
+The maximum number of pseudo-terminals is limited to 1000.
+It is not possible 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.
+.Sh FILES
+The files used by this
+pseudo-terminals implementation are:
+.Pp
+.Bl -tag -width ".Pa /dev/pts/[num]"
+.It Pa /dev/ptmx
+Control device, returns a file descriptor to a new master pseudo-terminal
+when opened. This device should not be opened directly. It's only
+available for binary compatibility. New devices should only be created
+though
+.Xr posix_openpt 2 .
+.It Pa /dev/pts/[num]
+Pseudo-terminal slave devices.
+.El
+.Sh DIAGNOSTICS
+None.
+.Sh SEE ALSO
+.Xr grantpt 3 ,
+.Xr posix_openpt 2 ,
+.Xr ptsname 3 ,
+.Xr pty 4 ,
+.Xr tty 4
+.Sh HISTORY
+A
+pseudo-terminal driver appeared in
+.Bx 4.2 .
+In
+.Fx 8.0 ,
+it was replaced with the
+.Nm
+driver.
+.Sh BUGS
+Packet mode has not been properly implemented in this version of
+.Fx .
+When enabled, it will always prepend
+.Dv TIOCPKT_DATA ,
+even if other events have been triggered.