mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-22 11:17:19 +00:00
141 lines
4.0 KiB
Groff
141 lines
4.0 KiB
Groff
.\" 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 int
|
|
.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 .
|