.\"	$OpenBSD: shm_open.3,v 1.3 2013/08/14 06:32:27 jmc Exp $
.\"
.\" Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: August 14 2013 $
.Dt SHM_OPEN 3
.Os
.Sh NAME
.Nm shm_open ,
.Nm shm_unlink ,
.Nm shm_mkstemp
.Nd create and destroy shared memory objects
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn shm_open "const char *path" "int flags" "mode_t mode"
.Ft int
.Fn shm_unlink "const char *path"
.Ft int
.Fn shm_mkstemp "char *template"
.Sh DESCRIPTION
The
.Fn shm_open
function opens a shared memory object and returns a file descriptor suitable
for use with
.Xr mmap 2 .
The
.Fa flags
argument has the same meaning as provided to
.Xr open 2
and must include at least
.Dv O_RDONLY
or
.Dv O_RDWR
and may also include a combination of
.Dv O_CREAT , O_EXCL ,
or
.Dv O_TRUNC .
This implementation forces the
.Fa mode
to be 0600 or 0400, and prohibits sharing between different UIDs.
.Pp
.Fn shm_unlink
is used to remove a shared memory object.
The object is not freed until all references to it have been released via
.Xr close 2 .
.Pp
If a temporary shared memory object is desired, the
.Fn shm_mkstemp
function should be preferred as it avoids several possible security
holes that tend to appear in programs trying to create their own unique
temporary names.
The
.Fa template
argument is a string with at least six trailing Xs as described in
.Xr mkstemp 3 .
.Sh RETURN VALUES
.Fn shm_open
and
.Fn shm_mkstemp
return a file descriptor on successful completion.
They may fail for any of the reasons listed in
.Xr open 2 .
.Sh SEE ALSO
.Xr mmap 2
.Sh STANDARDS
.Fn shm_open
and
.Fn shm_unlink
appear in
.St -p1003.1-2001 .
This implementation deviates from the standard by permitting less sharing.
.Pp
.Fn shm_mkstemp
is an extension.
.Sh AUTHORS
.An Ted Unangst Aq Mt tedu@openbsd.org .