178 lines
5.2 KiB
Groff
178 lines
5.2 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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.\" $Id: semctl.2,v 1.7 1997/03/18 23:57:17 bde Exp $
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.\"
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.Dd September 12, 1995
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.Dt SEMCTL 2
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.Os FreeBSD
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.Sh NAME
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.Nm semctl
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.Nd control operations on a semaphore set
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/ipc.h>
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.Fd #include <sys/sem.h>
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.Ft int
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.Fn semctl "int semid" "int semnum" "int cmd" ...
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.Sh DESCRIPTION
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.Fn Semctl
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performs the operation indicated by
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.Fa cmd
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on the semaphore set indicated by
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.Fa semid .
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A fourth argument, a
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.Fa "union semun arg" ,
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is required for certain values of
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.Fa cmd .
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For the commands that use the
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.Fa arg
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parameter,
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.Fa "union semun"
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is defined as follows:
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.Bd -literal
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.\"
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.\" From <sys/sem.h>:
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.\"
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union semun {
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int val; /* value for SETVAL */
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struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */
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u_short *array; /* array for GETALL & SETALL */
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};
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.Ed
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.Pp
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Commands are performed as follows:
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.\"
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.\" This section based on Stevens, _Advanced Programming in the UNIX
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.\" Environment_.
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.\"
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.Bl -tag -width IPC_RMIDXXX
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.It Dv IPC_STAT
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Fetch the semaphore set's
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.Fa "struct semid_ds" ,
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storing it in the memory pointed to by
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.Fa arg.buf .
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.It Dv IPC_SET
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Changes the
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.Fa sem_perm.uid ,
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.Fa sem_perm.gid ,
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and
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.Fa sem_perm.mode
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members of the semaphore set's
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.Fa "struct semid_ds"
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to match those of the struct pointed to by
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.Fa arg.buf .
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The calling process's effective uid must
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match either
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.Fa sem_perm.uid
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or
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.Fa sem_perm.cuid ,
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or it must have superuser privileges.
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.It IPC_RMID
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Immediately removes the semaphore set from the system. The calling
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process's effective uid must equal the semaphore set's
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.Fa sem_perm.uid
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or
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.Fa sem_perm.cuid ,
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or the process must have superuser privileges.
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.It Dv GETVAL
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Return the value of semaphore number
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.Fa semnum .
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.It Dv SETVAL
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Set the value of semaphore number
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.Fa semnum
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to
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.Fa arg.val .
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.It Dv GETPID
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Return the pid of the last process to perform an operation on
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semaphore number
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.Fa semnum .
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.It Dv GETNCNT
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Return the number of processes waiting for semaphore number
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.Fa semnum Ns 's
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value to become greater than its current value.
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.It Dv GETZCNT
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Return the number of processes waiting for semaphore number
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.Fa semnum Ns 's
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value to become 0.
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.It Dv GETALL
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Fetch the value of all of the semaphores in the set into the
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array pointed to by
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.Fa arg.array .
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.It Dv SETALL
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Set the values of all of the semaphores in the set to the values
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in the array pointed to by
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.Fa arg.array .
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.El
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.Pp
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The
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.Fa "struct semid_ds"
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is defined as follows:
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.Bd -literal
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.\"
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.\" Taken straight from <sys/sem.h>.
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.\"
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struct semid_ds {
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struct ipc_perm sem_perm; /* operation permission struct */
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struct sem *sem_base; /* pointer to first semaphore in set */
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u_short sem_nsems; /* number of sems in set */
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time_t sem_otime; /* last operation time */
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long sem_pad1; /* SVABI/386 says I need this here */
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time_t sem_ctime; /* last change time */
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/* Times measured in secs since */
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/* 00:00:00 GMT, Jan. 1, 1970 */
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long sem_pad2; /* SVABI/386 says I need this here */
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long sem_pad3[4]; /* SVABI/386 says I need this here */
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};
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.Ed
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.Sh RETURN VALUES
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On success, when
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.Fa cmd
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is one of GETVAL, GETNCNT, or GETZCNT,
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.Fn semctl
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returns the corresponding value; otherwise, 0 is returned.
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On failure, -1 is returned, and
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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 Semctl
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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 semaphore set corresponds to
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.Fa semid .
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.It Bq Er EINVAL
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.Fa semnum
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is not in the range of valid semaphores for given semaphore set.
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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 semaphore set'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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semaphore set.
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.Sh SEE ALSO
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.Xr semget 2 ,
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.Xr semop 2
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