241 lines
5.5 KiB
Groff
241 lines
5.5 KiB
Groff
.\" $NetBSD: shm_open.3,v 1.2 2013/12/20 13:48:45 wiz Exp $
|
|
.\"
|
|
.\" Copyright 2000 Massachusetts Institute of Technology
|
|
.\"
|
|
.\" Permission to use, copy, modify, and distribute this software and
|
|
.\" its documentation for any purpose and without fee is hereby
|
|
.\" granted, provided that both the above copyright notice and this
|
|
.\" permission notice appear in all copies, that both the above
|
|
.\" copyright notice and this permission notice appear in all
|
|
.\" supporting documentation, and that the name of M.I.T. not be used
|
|
.\" in advertising or publicity pertaining to distribution of the
|
|
.\" software without specific, written prior permission. M.I.T. makes
|
|
.\" no representations about the suitability of this software for any
|
|
.\" purpose. It is provided "as is" without express or implied
|
|
.\" warranty.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
|
|
.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
|
|
.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
|
|
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
|
|
.\" SHALL M.I.T. 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd December 19, 2013
|
|
.Dt SHM_OPEN 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm shm_open , shm_unlink
|
|
.Nd "shared memory object operations"
|
|
.Sh LIBRARY
|
|
.Lb librt
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/mman.h
|
|
.In fcntl.h
|
|
.Ft int
|
|
.Fn shm_open "const char *name" "int flags" "mode_t mode"
|
|
.Ft int
|
|
.Fn shm_unlink "const char *name"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn shm_open
|
|
function creates or opens a
|
|
.Tn POSIX
|
|
shared memory object named
|
|
.Fa name .
|
|
The
|
|
.Fa flags
|
|
argument contains a subset of the flags used by
|
|
.Xr open 2 .
|
|
An access mode of either
|
|
.Dv O_RDONLY
|
|
or
|
|
.Dv O_RDWR
|
|
must be included in
|
|
.Fa flags .
|
|
The optional flags
|
|
.Dv O_CREAT ,
|
|
.Dv O_EXCL ,
|
|
and
|
|
.Dv O_TRUNC
|
|
may also be specified.
|
|
.Pp
|
|
If
|
|
.Dv O_CREAT
|
|
is specified,
|
|
then a new shared memory object named
|
|
.Fa name
|
|
will be created if it does not exist.
|
|
In this case,
|
|
the shared memory object is created with mode
|
|
.Fa mode
|
|
subject to the process' umask value.
|
|
If both the
|
|
.Dv O_CREAT
|
|
and
|
|
.Dv O_EXCL
|
|
flags are specified and a shared memory object named
|
|
.Fa path
|
|
already exists,
|
|
then
|
|
.Fn shm_open
|
|
will fail with
|
|
.Er EEXIST .
|
|
.Pp
|
|
Newly created objects start off with a size of zero.
|
|
If an existing shared memory object is opened with
|
|
.Dv O_RDWR
|
|
and the
|
|
.Dv O_TRUNC
|
|
flag is specified,
|
|
then the shared memory object will be truncated to a size of zero.
|
|
The size of the object can be adjusted via
|
|
.Xr ftruncate 2
|
|
and queried via
|
|
.Xr fstat 2 .
|
|
.Pp
|
|
The new descriptor is set to close during
|
|
.Xr execve 2
|
|
system calls;
|
|
see
|
|
.Xr close 2
|
|
and
|
|
.Xr fcntl 2 .
|
|
.Pp
|
|
The
|
|
.Fn shm_unlink
|
|
system call removes a shared memory object named
|
|
.Fa path .
|
|
.Sh RETURN VALUES
|
|
If successful,
|
|
.Fn shm_open
|
|
returns a non-negative integer,
|
|
and
|
|
.Fn shm_unlink
|
|
returns zero.
|
|
Both functions return -1 on failure, and set
|
|
.Va errno
|
|
to indicate the error.
|
|
.Sh COMPATIBILITY
|
|
The
|
|
.Fa path
|
|
argument does not necessarily represent a pathname (although it does in
|
|
most other implementations).
|
|
Two processes opening the same
|
|
.Fa path
|
|
are guaranteed to access the same shared memory object if and only if
|
|
.Fa path
|
|
begins with a slash
|
|
.Pq Ql \&/
|
|
character.
|
|
.Pp
|
|
Only the
|
|
.Dv O_RDONLY ,
|
|
.Dv O_RDWR ,
|
|
.Dv O_CREAT ,
|
|
.Dv O_EXCL ,
|
|
and
|
|
.Dv O_TRUNC
|
|
flags may be used in portable programs.
|
|
.Pp
|
|
The result of using
|
|
.Xr open 2 ,
|
|
.Xr read 2 ,
|
|
or
|
|
.Xr write 2
|
|
on a shared memory object, or on the descriptor returned by
|
|
.Fn shm_open ,
|
|
is undefined.
|
|
It is also undefined whether the shared memory object itself, or its
|
|
contents, persist across reboots.
|
|
.Sh ERRORS
|
|
The following errors are defined for
|
|
.Fn shm_open :
|
|
.Bl -tag -width Er
|
|
.It Bq Er EACCES
|
|
The required permissions (for reading or reading and writing) are denied.
|
|
.It Bq Er EEXIST
|
|
.Dv O_CREAT
|
|
and
|
|
.Dv O_EXCL
|
|
are specified and the named shared memory object does exist.
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa path
|
|
argument points outside the process' allocated address space.
|
|
.It Bq Er EINVAL
|
|
A flag other than
|
|
.Dv O_RDONLY ,
|
|
.Dv O_RDWR ,
|
|
.Dv O_CREAT ,
|
|
.Dv O_EXCL ,
|
|
or
|
|
.Dv O_TRUNC
|
|
was included in
|
|
.Fa flags ;
|
|
or the
|
|
.Fa path
|
|
does not begin with a slash
|
|
.Pq Ql \&/
|
|
character.
|
|
.It Bq Er EMFILE
|
|
The process has already reached its limit for open file descriptors.
|
|
.It Bq Er ENAMETOOLONG
|
|
The entire pathname exceeded
|
|
.Brq Dv PATH_MAX
|
|
characters.
|
|
.It Bq Er ENFILE
|
|
The system file table is full.
|
|
.It Bq Er ENOENT
|
|
.Dv O_CREAT
|
|
is specified and the named shared memory object does not exist.
|
|
.It Bq Er ENOTSUP
|
|
Not supported, most likely due to missing or incorrect
|
|
.Pa /var/shm
|
|
mount.
|
|
.El
|
|
.Pp
|
|
The following errors are defined for
|
|
.Fn shm_unlink :
|
|
.Bl -tag -width Er
|
|
.It Bq Er EACCES
|
|
The required permissions are denied.
|
|
.Fn shm_unlink
|
|
requires write permission to the shared memory object.
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa path
|
|
argument points outside the process' allocated address space.
|
|
.It Bq Er ENAMETOOLONG
|
|
The entire pathname exceeded
|
|
.Brq Dv PATH_MAX
|
|
characters.
|
|
.It Bq Er ENOENT
|
|
The named shared memory object does not exist.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr close 2 ,
|
|
.Xr fstat 2 ,
|
|
.Xr ftruncate 2 ,
|
|
.Xr mmap 2 ,
|
|
.Xr munmap 2
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn shm_open
|
|
and
|
|
.Fn shm_unlink
|
|
functions are expected to conform to
|
|
.St -p1003.1b-93 .
|
|
.Sh HISTORY
|
|
These functions first appeared in
|
|
.Nx 7.0 .
|