minix/lib/libc/sys/vfork.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

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Groff

.\" $NetBSD: vfork.2,v 1.24 2003/08/07 16:44:11 agc 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:
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.\" 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. 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 January 3, 1998
.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
.Nm
system call creates a new process that does not have a new
virtual address space, but rather shares address space with the
parent, thus avoiding potentially expensive copy-on-write operations
normally associated with creating a new process.
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
.Nm
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
.Nm
system call returns 0 in the child's context and (later) the pid
of the child in the parent's context.
.Pp
The
.Nm
system call 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
standard I/O data structures
in the parent process.
(Even with
.Xr fork 2
it is wrong to call
.Xr exit 3
since buffered data would then be flushed twice.)
.Sh RETURN VALUES
Same as for
.Xr fork 2 .
.Sh ERRORS
Same as for
.Xr fork 2 .
.Sh SEE ALSO
.Xr execve 2 ,
.Xr fork 2 ,
.Xr sigaction 2 ,
.Xr wait 2
.Sh HISTORY
The
.Fn vfork
function call appeared in
.Bx 3.0 .
In
.Bx 4.4 ,
the semantics were changed to only suspend the parent.
The original semantics were reintroduced in
.Nx 1.4 .
.Sh BUGS
.\" XXX We reintroduced the original semantics.
.\" 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 other ways of speeding up the fork process may be developed in
the future.
.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.