mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-20 11:11:24 +00:00
064f007493
converted them into .Fn macros where appropriate. Also fixed up some minor formatting problems.
127 lines
3.9 KiB
Groff
127 lines
3.9 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
|
|
.\"
|
|
.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 int
|
|
.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 2 .
|
|
.Fn Vfork
|
|
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 3
|
|
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 2 .
|
|
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 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 fork 2 ,
|
|
.Xr execve 2 ,
|
|
.Xr sigvec 2 ,
|
|
.Xr wait 2 ,
|
|
.Sh DIAGNOSTICS
|
|
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
|
|
.Xr vfork 2
|
|
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
|
|
.Nm
|
|
function call appeared in
|
|
.Bx 3.0 .
|