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139 lines
4.3 KiB
Groff
139 lines
4.3 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 July 17, 1995
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.Dt SHMCTL 2
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.Os
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.Sh NAME
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.Nm shmctl
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.Nd shared memory control
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In machine/param.h
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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 int
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.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf"
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.Sh DESCRIPTION
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Performs the action specified by
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.Fa cmd
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on the shared memory segment identified by
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.Fa shmid :
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.Bl -tag -width SHM_UNLOCKX
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.It Dv IPC_STAT
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Fetch the segment's
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.Fa "struct shmid_ds" ,
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storing it in the memory pointed to by
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.Fa buf .
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.\"
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.\" XXX need to make sure that this is correct for FreeBSD
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.\"
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.It Dv IPC_SET
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Changes the
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.Fa shm_perm.uid ,
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.Fa shm_perm.gid ,
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and
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.Fa shm_perm.mode
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members of the segment's
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.Fa "struct shmid_ds"
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to match those of the struct pointed to by
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.Fa buf .
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The calling process's effective uid must
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match either
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.Fa shm_perm.uid
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or
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.Fa shm_perm.cuid ,
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or it must have superuser privileges.
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.It Dv IPC_RMID
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Removes the segment from the system. The removal will not take
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effect until all processes having attached the segment have exited;
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however, once the IPC_RMID operation has taken place, no further
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processes will be allowed to attach the segment. For the operation
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to succeed, the calling process's effective uid must match
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.Fa shm_perm.uid
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or
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.Fa shm_perm.cuid ,
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or the process must have superuser privileges.
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.\" .It Dv SHM_LOCK
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.\" Locks the segment in memory. The calling process must have
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.\" superuser privileges. Not implemented in FreeBSD.
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.\" .It Dv SHM_UNLOCK
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.\" Unlocks the segment from memory. The calling process must
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.\" have superuser privileges. Not implemented in FreeBSD.
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.El
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.Pp
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The
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.Vt shmid_ds
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structure is defined as follows:
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.\"
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.\" I fiddled with the spaces a bit to make it fit well when viewed
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.\" with nroff, but otherwise it's straight from sys/shm.h
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.\"
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.Bd -literal
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struct shmid_ds {
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struct ipc_perm shm_perm; /* operation permission structure */
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int shm_segsz; /* size of segment in bytes */
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pid_t shm_lpid; /* process ID of last shared memory op */
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pid_t shm_cpid; /* process ID of creator */
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short shm_nattch; /* number of current attaches */
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time_t shm_atime; /* time of last shmat() */
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time_t shm_dtime; /* time of last shmdt() */
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time_t shm_ctime; /* time of last change by shmctl() */
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void *shm_internal; /* sysv stupidity */
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};
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.Ed
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.Sh RETURN VALUES
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.Rv -std shmctl
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.Sh ERRORS
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The
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.Fn shmctl
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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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Invalid operation, or
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no shared memory segment was found corresponding to
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.Fa shmid .
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.\"
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.\" XXX I think the following is right: ipcperm() only returns EPERM
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.\" when an attempt is made to modify (IPC_M) by a non-creator
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.\" non-owner
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.It Bq Er EPERM
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The calling process's effective uid does not match the uid of
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the shared memory segment's owner or creator.
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.It Bq Er EACCES
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Permission denied due to mismatch between operation and mode of
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shared memory segment.
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.El
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.Sh "SEE ALSO"
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.Xr shmat 2 ,
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.Xr shmdt 2 ,
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.Xr shmget 2 ,
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.Xr ftok 3
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