136 lines
4.1 KiB
Groff
136 lines
4.1 KiB
Groff
.\" $NetBSD: shmat.2,v 1.11 2001/09/16 01:39:02 wiz Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd August 25, 1999
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.Dt SHMAT 2
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.Os
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.Sh NAME
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.Nm shmat ,
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.Nm shmdt
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.Nd map/unmap shared memory
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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/shm.h>
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.Ft void *
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.Fn shmat "int shmid" "const void *shmaddr" "int shmflg"
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.Ft int
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.Fn shmdt "const void *shmaddr"
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.Sh DESCRIPTION
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.Fn shmat
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maps the shared memory segment associated with the shared memory identifier
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.Fa shmid
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into the address space of the calling process. The address at which the
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segment is mapped is determined by the
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.Fa shmaddr
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parameter. If it is equal to 0, the system will pick an address itself.
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Otherwise, an attempt is made to map the shared memory segment at the
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address
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.Fa shmaddr
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specifies. If
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.Dv SHM_RND
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is set in
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.Fa shmflg ,
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the system will round the address down to a multiple of
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.Dv SHMLBA
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bytes
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.Pf ( Dv SHMLBA
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is defined in
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.Aq Pa sys/shm.h ) .
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.Pp
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A shared memory segment can be mapped read-only by specifying the
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.Dv SHM_RDONLY
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flag in
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.Fa shmflg .
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.Pp
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.Fn shmdt
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unmaps the shared memory segment that is currently mapped at
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.Fa shmaddr
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from the calling process' address space.
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.Fa shmaddr
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must be a value returned by a prior
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.Fn shmat
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call. A shared memory segment will remain in existence until it is
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removed by a call to
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.Xr shmctl 2
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with the
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.Dv IPC_RMID
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command.
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.Sh RETURN VALUES
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.Fn shmat
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returns the address at which the shared memory segment has been mapped into
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the calling process' address space when successful,
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.Fn shmdt
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returns 0 on successful completion. Otherwise, a value of -1 is returned,
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and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn shmat
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The calling process has no permission to access this shared memory segment.
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.It Bq Er ENOMEM
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There is not enough available data space for the calling process to
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map the shared memory segment.
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.It Bq Er EINVAL
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.Fa shmid
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is not a valid shared memory identifier.
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.Pp
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.Fa shmaddr
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specifies an illegal address.
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.It Bq Er EMFILE
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The number of shared memory segments has reached the system-wide limit.
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.El
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.Pp
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.Fn shmdt
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa shmaddr
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is not the start address of a mapped shared memory segment.
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.El
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.Sh SEE ALSO
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.Xr mmap 2 ,
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.Xr shmctl 2 ,
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.Xr shmget 2
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.Sh STANDARDS
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The
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.Nm shmat
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and
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.Nm shmdt
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system calls conform to
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.St -xsh5 .
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.Sh HISTORY
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Shared memory segments appeared in the first release of
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.At V .
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