ea7e7006db
Based on the description in Linux man page. Reviewed by: markj, ngie (previous version) Sponsored by: Mellanox Technologies MFC after: 1 week Differential revision: https://reviews.freebsd.org/D18837
157 lines
3.7 KiB
Groff
157 lines
3.7 KiB
Groff
.\"
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.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
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.\"
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``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 DEVELOPERS 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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.\" $FreeBSD$
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.\"
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.Dd January 14, 2019
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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 attach or detach shared memory
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/ipc.h
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.In sys/shm.h
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.Ft void *
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.Fn shmat "int shmid" "const void *addr" "int flag"
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.Ft int
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.Fn shmdt "const void *addr"
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.Sh DESCRIPTION
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The
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.Fn shmat
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system call
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attaches the shared memory segment identified by
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.Fa shmid
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to the calling process's address space.
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The address where the segment
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is attached is determined as follows:
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.\"
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.\" These are cribbed almost exactly from Stevens, _Advanced Programming in
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.\" the UNIX Environment_.
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.\"
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.Bl -bullet
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.It
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If
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.Fa addr
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is 0, the segment is attached at an address selected by the
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kernel.
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.It
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If
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.Fa addr
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is nonzero and
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.Va SHM_RND
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is not specified in
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.Fa flag ,
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the segment is attached the specified address.
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.It
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If
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.Fa addr
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is specified and
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.Va SHM_RND
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is specified,
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.Fa addr
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is rounded down to the nearest multiple of SHMLBA.
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.El
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.Pp
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If the
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.Va SHM_REMAP
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flag is specified and the passed
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.Fa addr
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is not
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.Dv NULL ,
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any existing mappings in the virtual addresses range are
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cleared before the segment is attached.
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If the flag is not specified,
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.Fa addr
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is not
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.Dv NULL ,
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and the virtual address range contains
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some pre-existing mappings, the
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.Fn shmat
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call fails.
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.Pp
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The
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.Fn shmdt
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system call
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detaches the shared memory segment at the address specified by
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.Fa addr
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from the calling process's address space.
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.Sh RETURN VALUES
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Upon success,
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.Fn shmat
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returns the address where the segment is attached; otherwise, -1
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is returned and
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.Va errno
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is set to indicate the error.
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.Pp
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.Rv -std shmdt
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.Sh ERRORS
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The
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.Fn shmat
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system call
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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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No shared memory segment was found corresponding to
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.Fa shmid .
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.It Bq Er EINVAL
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The
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.Fa addr
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argument
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was not an acceptable address.
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.It Bq Er ENOMEM
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The specified
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.Fa addr
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cannot be used for mapping, for instance due to the amount of available
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space being smaller than the segment size,
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or because pre-existing mappings are in the range and no
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.Va SHM_REMAP
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flag was provided.
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.It Bq Er EMFILE
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Failed to attach the shared memory segment because the per-process
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.Va kern.ipc.shmseg
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.Xr sysctl 3
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limit was reached.
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.El
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.Pp
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The
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.Fn shmdt
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system call
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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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The
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.Fa addr
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argument
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does not point to a shared memory segment.
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.El
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.Sh "SEE ALSO"
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.Xr shmctl 2 ,
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.Xr shmget 2
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