[apple/xnu.git] / bsd / man / man2 / vfork.2

.\"	$NetBSD: vfork.2,v 1.6 1995/02/27 12:39:30 cgd Exp $
.\"
.\" 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
.\"
.Dd June 4, 1993
.Dt VFORK 2
.Os BSD 4
.Sh NAME
.Nm vfork
.Nd spawn new process in a virtual memory efficient way
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft pid_t
.Fn vfork void
.Sh DESCRIPTION
.Fn Vfork
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 .
.Fn Vfork
differs from
.Xr fork
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
.Fn Vfork
returns 0 in the child's context and (later) the pid of the child in
the parent's context.
.Pp
.Fn Vfork
can normally be used just like
.Xr fork .
It does not work, however, to return while running in the childs 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
rather than
.Xr exit
if you can't
.Xr execve ,
since
.Xr exit
will flush and close standard I/O channels, and thereby mess up the
parent processes standard I/O data structures.
(Even with
.Xr fork
it is wrong to call
.Xr exit
since buffered data would then be flushed twice.)
.Sh SEE ALSO
.Xr fork 2 ,
.Xr execve 2 ,
.Xr sigaction 2 ,
.Xr wait 2 
.Sh DIAGNOSTICS
Same as for
.Xr fork .
.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
.Xr vfork
as it will, in that case, be made synonymous to
.Xr fork .
.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
function call appeared in
.Bx 3.0 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: vfork.2,v 1.6 1995/02/27 12:39:30 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
	35	.\"
	36	.Dd June 4, 1993
	37	.Dt VFORK 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm vfork
	41	.Nd spawn new process in a virtual memory efficient way
	42	.Sh SYNOPSIS
	43	.Fd #include <unistd.h>
	44	.Ft pid_t
	45	.Fn vfork void
	46	.Sh DESCRIPTION
	47	.Fn Vfork
	48	can be used to create new processes without fully copying the address
	49	space of the old process, which is horrendously inefficient in a paged
	50	environment. It is useful when the purpose of
	51	.Xr fork 2
	52	would have been to create a new system context for an
	53	.Xr execve .
	54	.Fn Vfork
	55	differs from
	56	.Xr fork
	57	in that the child borrows the parent's memory and thread of
	58	control until a call to
	59	.Xr execve 2
	60	or an exit (either by a call to
	61	.Xr exit 2
	62	or abnormally.)
	63	The parent process is suspended while the child is using its resources.
	64	.Pp
65	.Fn Vfork
66	returns 0 in the child's context and (later) the pid of the child in
67	the parent's context.
68	.Pp
69	.Fn Vfork
70	can normally be used just like
71	.Xr fork .
72	It does not work, however, to return while running in the childs context
73	from the procedure that called
74	.Fn vfork
75	since the eventual return from
76	.Fn vfork
77	would then return to a no longer existent stack frame.
78	Be careful, also, to call
79	.Xr _exit
80	rather than
81	.Xr exit
82	if you can't
83	.Xr execve ,
84	since
85	.Xr exit
86	will flush and close standard I/O channels, and thereby mess up the
87	parent processes standard I/O data structures.
88	(Even with
89	.Xr fork
90	it is wrong to call
91	.Xr exit
92	since buffered data would then be flushed twice.)
93	.Sh SEE ALSO
94	.Xr fork 2 ,
95	.Xr execve 2 ,
96	.Xr sigaction 2 ,
91447636	97	.Xr wait 2
9bccf70c A	98	.Sh DIAGNOSTICS
	99	Same as for
	100	.Xr fork .
	101	.Sh BUGS
	102	This system call will be eliminated when proper system sharing
	103	mechanisms are implemented.
	104	Users should not depend on the memory
	105	sharing semantics of
	106	.Xr vfork
	107	as it will, in that case, be made synonymous to
	108	.Xr fork .
	109	.Pp
	110	To avoid a possible deadlock situation,
	111	processes that are children in the middle
	112	of a
	113	.Fn vfork
	114	are never sent
	115	.Dv SIGTTOU
	116	or
	117	.Dv SIGTTIN
	118	signals; rather,
	119	output or
	120	.Xr ioctl 2
	121	calls
	122	are allowed
	123	and input attempts result in an end-of-file indication.
	124	.Sh HISTORY
	125	The
	126	.Fn vfork
	127	function call appeared in
	128	.Bx 3.0 .