freebsd-skq/lib/libc/sys/posix_openpt.2
ed cc3116a938 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
2008-08-20 08:31:58 +00:00

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.\" 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.
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.\" Portions of this text are reprinted and reproduced in electronic form
.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
.\" Portable Operating System Interface (POSIX), The Open Group Base
.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
.\" Electrical and Electronics Engineers, Inc and The Open Group. In the
.\" event of any discrepancy between this version and the original IEEE and
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.\" $FreeBSD$
.\"
.Dd August 20, 2008
.Dt POSIX_OPENPT 2
.Os
.Sh NAME
.Nm posix_openpt
.Nd "open a pseudo-terminal device"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.In fcntl.h
.Ft int
.Fn posix_openpt "int oflag"
.Sh DESCRIPTION
The
.Fn posix_openpt
function allocates a new pseudo-terminal and establishes a connection
with its master device.
A slave device shall be created in
.Pa /dev/pts .
After the pseudo-terminal has been allocated, the slave device should
have the proper permissions before it can be used (see
.Xr grantpt 3 ) .
The name of the slave device can be determined by calling
.Xr ptsname 3 .
.Pp
The file status flags and file access modes of the open file description
shall be set according to the value of
.Fa oflag .
Values for
.Fa oflag
are constructed by a bitwise-inclusive OR of flags from the following
list, defined in
.In fcntl.h :
.Bl -tag -width ".Dv O_NOCTTY"
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
If set
.Fn posix_openpt
shall not cause the terminal device to become the controlling terminal
for the process.
.El
.Pp
The
.Fn posix_openpt
function shall fail when
.Fa oflag
contains other values.
.Sh RETURN VALUES
Upon successful completion, the
.Fn posix_openpt
function shall allocate a new pseudo-terminal device and return a
non-negative integer representing a file descriptor, which is connected
to its master device.
Otherwise, -1 shall be returned and errno set to indicate the error.
.Sh ERRORS
The
.Fn posix_openpt
function shall fail if:
.Bl -tag -width Er
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EINVAL
The value of
.Fa oflag
is not valid.
.It Bq Er EAGAIN
Out of pseudo-terminal resources.
.El
.Sh SEE ALSO
.Xr pts 4 ,
.Xr ptsname 3 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn posix_openpt
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn posix_openpt
function appeared in
.Fx 5.0 .
In
.Fx 8.0 ,
this function was changed to a system call.
.Sh NOTES
The flag
.Dv O_NOCTTY
is included for compatibility; in
.Fx ,
opening a terminal does not cause it to become a process's controlling
terminal.
.Sh AUTHORS
.An Ed Schouten Aq ed@FreeBSD.org