195 lines
4.5 KiB
Groff
195 lines
4.5 KiB
Groff
.\"
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.\" Copyright 2000 Massachusetts Institute of Technology
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.\"
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.\" Permission to use, copy, modify, and distribute this software and
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.\" its documentation for any purpose and without fee is hereby
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.\" granted, provided that both the above copyright notice and this
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.\" permission notice appear in all copies, that both the above
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.\" copyright notice and this permission notice appear in all
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.\" supporting documentation, and that the name of M.I.T. not be used
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.\" in advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission. M.I.T. makes
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.\" no representations about the suitability of this software for any
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.\" purpose. It is provided "as is" without express or implied
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.\" warranty.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 24, 2000
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.Dt SHM_OPEN 3
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.Os
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.Sh NAME
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.Nm shm_open
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.Nd open or create a shared memory object
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.Nm shm_unlink
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.Nd remove a shared memory object
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/mman.h>
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.Ft int
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.Fn shm_open "const char *path" "int flags" "mode_t mode"
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.Ft int
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.Fn shm_unlink "const char *path"
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.Sh DESCRIPTION
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The
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.Nm shm_open
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function opens (or optionally creates) a
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.Tn POSIX
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shared memory object named
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.Fa path .
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The
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.Nm shm_unlink
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function removes a shared memory object named
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.Fa path .
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.Pp
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In the
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.Fx
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implementation,
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.Tn POSIX
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shared memory objects are implemented as ordinary files.
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The
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.Nm shm_open
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and
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.Nm shm_unlink
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act as wrappers around the
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.Xr open 2
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and
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.Xr unlink 2
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routines, and
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.Fa path ,
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.Fa flags ,
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and
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.Fa mode
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arguments are as specified for those functions.
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The
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.Fa flags
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argument is checked to ensure that the access mode specified is not
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.Dv O_WRONLY
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(which is not defined for shared memory objects).
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.Pp
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In addition, the
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.Fx
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implementation causes
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.Fn mmap
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of a descriptor returned by
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.Nm shm_open
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to behave as if the
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.Dv MAP_NOSYNC
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flag had been specified to
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.Xr mmap 2 .
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(It does so by setting a special file flag using
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.Xr fcntl 2 . )
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.Pp
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The
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.Nm shm_unlink
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function makes no effort to ensure that
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.Fa path
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refers to a shared memory object.
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.Sh PORTABILITY
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The
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.Fa path
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argument does not necessarily represent a pathname (although it does in this
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and most other implementations).
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Two processes opening the same
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.Fa path
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are guaranteed to access the same shared memory object if and only if
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.Fa path
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begins with a slash
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.Pq Ql \&/
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character.
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.Pp
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Only the
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.Dv O_RDONLY ,
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.Dv O_RDWR ,
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.Dv O_CREAT ,
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.Dv O_EXCL ,
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and
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.Dv O_TRUNC
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flags may be used in portable programs.
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.Pp
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The result of using
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.Xr open 2 ,
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.Xr read 2 ,
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or
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.Xr write 2
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on a shared memory object, or on the descriptor returned by
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.Fn shm_open ,
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is undefined.
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It is also undefined whether the shared memory object itself, or its
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contents, persist across reboots.
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.Sh RETURN VALUES
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If successful,
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.Fn shm_open
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returns a non-negative integer;
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.Fn shm_unlink
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returns zero.
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Both functions return -1 on failure, and set
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.Va errno
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to indicate the error.
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.Sh ERRORS
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The
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.Fn shm_open
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and
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.Fn shm_unlink
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functions can fail with any error defined for
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.Fn open
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and
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.Fn unlink ,
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respectively. In addition, the following errors are defined for
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.Fn shm_open :
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The object named by
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.Fa path
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is not a shared memory object
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(i.e., it is not a regular file).
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.It Bq Er EINVAL
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The
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.Fa flags
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argument to
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.Fn shm_open
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specifies an access mode of
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.Dv O_WRONLY .
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.El
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.Sh SEE ALSO
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.Xr mmap 2 ,
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.Xr munmap 2 ,
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.Xr open 2 ,
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.Xr unlink 2
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.Sh STANDARDS
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The
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.Nm shm_open
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and
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.Nm shm_unlink
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functions are believed to conform to
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.St -p1003.1b .
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.Sh HISTORY
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The
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.Nm shm_open
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and
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.Nm shm_unlink
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functions first appeared in
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.Fx 5.0 .
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.Sh AUTHORS
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.An Garrett A. Wollman Aq wollman@FreeBSD.org
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(C library support and this manual page)
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.Pp
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.An Matthew Dillon Aq dillon@FreeBSD.org
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.Pq Dv MAP_NOSYNC
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