freebsd-nq/lib/libc/sys/vfork.2

.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 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
.\" 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
.\" 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)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)vfork.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd June 4, 1993
.Dt VFORK 2
.Os
.Sh NAME
.Nm vfork
.Nd spawn new process in a virtual memory efficient way
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft pid_t
.Fn vfork void
.Sh DESCRIPTION
The
.Fn vfork
system call
can be used to create new processes without fully copying the address
space of the old process, which is horrendously inefficient in a paged
environment.  It is useful when the purpose of
.Xr fork 2
would have been to create a new system context for an
.Xr execve 2 .
The
.Fn vfork
system call
differs from
.Xr fork 2
in that the child borrows the parent's memory and thread of
control until a call to
.Xr execve 2
or an exit (either by a call to
.Xr _exit 2
or abnormally).
The parent process is suspended while the child is using its resources.
.Pp
The
.Fn vfork
system call
returns 0 in the child's context and (later) the pid of the child in
the parent's context.
.Pp
The
.Fn vfork
system call
can normally be used just like
.Xr fork 2 .
It does not work, however, to return while running in the child's context
from the procedure that called
.Fn vfork
since the eventual return from
.Fn vfork
would then return to a no longer existent stack frame.
Be careful, also, to call
.Xr _exit 2
rather than
.Xr exit 3
if you can't
.Xr execve 2 ,
since
.Xr exit 3
will flush and close standard I/O channels, and thereby mess up the
parent processes standard I/O data structures.
(Even with
.Xr fork 2
it is wrong to call
.Xr exit 3
since buffered data would then be flushed twice.)
.Sh SEE ALSO
.Xr execve 2 ,
.Xr fork 2 ,
.Xr rfork 2 ,
.Xr sigvec 2 ,
.Xr wait 2 ,
.Xr _exit 2 ,
.Xr exit 3
.Sh RETURN VALUES
Same as for
.Xr fork 2 .
.Sh BUGS
This system call will be eliminated when proper system sharing
mechanisms are implemented.
Users should not depend on the memory
sharing semantics of
.Fn vfork
as it will, in that case, be made synonymous to
.Xr fork 2 .
.Pp
To avoid a possible deadlock situation,
processes that are children in the middle
of a
.Fn vfork
are never sent
.Dv SIGTTOU
or
.Dv SIGTTIN
signals; rather,
output or
.Xr ioctl 2
calls
are allowed
and input attempts result in an end-of-file indication.
.Sh HISTORY
The
.Fn vfork
system call appeared in
.Bx 2.9 .
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\" Copyright (c) 1980, 1991, 1993`
			`.\" The Regents of the University of California. All rights reserved.`
			`.\"`
			`.\" Redistribution and use in source and binary forms, with or without`
			`.\" modification, are permitted provided that the following conditions`
			`.\" are met:`
			`.\" 1. Redistributions of source code must retain the above copyright`
			`.\" notice, this list of conditions and the following disclaimer.`
			`.\" 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
			`.\" 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`
			`.\" 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)`
			`.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT`
			`.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY`
			`.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF`
			`.\" SUCH DAMAGE.`
			`.\"`
			`.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93`
$Id$ -> $FreeBSD$ 1999-08-28 00:22:10 +00:00			`.\" $FreeBSD$`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\"`
			`.Dd June 4, 1993`
			`.Dt VFORK 2`
mdoc(7) police: removed HISTORY info from the .Os call. 2001-07-10 13:41:46 +00:00			`.Os`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh NAME`
			`.Nm vfork`
			`.Nd spawn new process in a virtual memory efficient way`
Introduce ".Lb" macro to libc manpages. More libraries manpages updates following. 2000-04-21 09:42:15 +00:00			`.Sh LIBRARY`
			`.Lb libc`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh SYNOPSIS`
mdoc(7) police: Use the new .In macro for #include statements. 2001-10-01 16:09:29 +00:00			`.In unistd.h`
Correct the return value of vfork(2) and rfork(2) in their manual page function prototypes. 2003-04-27 21:01:34 +00:00			`.Ft pid_t`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Fn vfork void`
			`.Sh DESCRIPTION`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
			`.Fn vfork`
			`system call`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`can be used to create new processes without fully copying the address`
			`space of the old process, which is horrendously inefficient in a paged`
			`environment. It is useful when the purpose of`
			`.Xr fork 2`
			`would have been to create a new system context for an`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr execve 2 .`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
			`.Fn vfork`
			`system call`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`differs from`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr fork 2`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`in that the child borrows the parent's memory and thread of`
			`control until a call to`
			`.Xr execve 2`
			`or an exit (either by a call to`
Don't mention exit(3) in explanation; _exit(2) is a better choice. 1998-11-23 03:23:14 +00:00			`.Xr _exit 2`
Added missing section numbers to a bunch of .Xr macros, or converted them into .Fn macros where appropriate. Also fixed up some minor formatting problems. 1996-03-27 20:49:07 +00:00			`or abnormally).`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`The parent process is suspended while the child is using its resources.`
			`.Pp`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
			`.Fn vfork`
			`system call`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`returns 0 in the child's context and (later) the pid of the child in`
			`the parent's context.`
			`.Pp`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
			`.Fn vfork`
			`system call`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`can normally be used just like`
Added missing section numbers to a bunch of .Xr macros, or converted them into .Fn macros where appropriate. Also fixed up some minor formatting problems. 1996-03-27 20:49:07 +00:00			`.Xr fork 2 .`
english(4) police. 2002-12-27 12:15:40 +00:00			`It does not work, however, to return while running in the child's context`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`from the procedure that called`
			`.Fn vfork`
			`since the eventual return from`
			`.Fn vfork`
			`would then return to a no longer existent stack frame.`
			`Be careful, also, to call`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr _exit 2`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`rather than`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr exit 3`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`if you can't`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr execve 2 ,`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`since`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr exit 3`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`will flush and close standard I/O channels, and thereby mess up the`
			`parent processes standard I/O data structures.`
			`(Even with`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr fork 2`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`it is wrong to call`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr exit 3`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`since buffered data would then be flushed twice.)`
			`.Sh SEE ALSO`
			`.Xr execve 2 ,`
comma typos 1996-12-23 23:09:55 +00:00			`.Xr fork 2 ,`
Add cross-references to rfork(2). 1997-11-18 03:59:30 +00:00			`.Xr rfork 2 ,`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Xr sigvec 2 ,`
Expanded cross references. 1998-01-02 19:22:52 +00:00			`.Xr wait 2 ,`
mdoc(7) police: sort SEE ALSO xrefs (sort -b -f +2 -3 +1 -2). 2001-07-06 16:46:48 +00:00			`.Xr _exit 2 ,`
Expanded cross references. 1998-01-02 19:22:52 +00:00			`.Xr exit 3`
Rename the DIAGNOSTICS sections in several man pages to RETURN VALUES like they should be. 1997-01-12 00:09:02 +00:00			`.Sh RETURN VALUES`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`Same as for`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr fork 2 .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh BUGS`
			`This system call will be eliminated when proper system sharing`
Remove whitespace at EOL. 2001-07-15 07:53:42 +00:00			`mechanisms are implemented.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`Users should not depend on the memory`
			`sharing semantics of`
mdoc(7) police: Deal with self-xrefs. 2002-12-24 13:41:48 +00:00			`.Fn vfork`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`as it will, in that case, be made synonymous to`
Fixed a bunch of man page cross references that were in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section. 1996-02-15 20:07:05 +00:00			`.Xr fork 2 .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Pp`
			`To avoid a possible deadlock situation,`
			`processes that are children in the middle`
			`of a`
			`.Fn vfork`
			`are never sent`
			`.Dv SIGTTOU`
			`or`
			`.Dv SIGTTIN`
			`signals; rather,`
			`output or`
			`.Xr ioctl 2`
			`calls`
			`are allowed`
			`and input attempts result in an end-of-file indication.`
			`.Sh HISTORY`
			`The`
Correctly use .Fn instead of .Nm to reference function names in a bunch of man pages. Use the correct .Bx (BSD UNIX) or .At (AT&T UNIX) macros instead of explicitly specifying the version in the text in a bunch of man pages. 1996-08-22 23:31:07 +00:00			`.Fn vfork`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`system call appeared in`
First appeared in 2.9BSD, not 3.0. PR: 19263 Submitted by: NOKUBI Hirotaka <nokubi@ff.iij4u.or.jp> Obtained from: Open\|NetBSD 2000-07-08 18:17:12 +00:00			`.Bx 2.9 .`