160 lines
4.1 KiB
Groff
160 lines
4.1 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 February 7, 2016
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.Dt SEMGET 2
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.Os
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.Sh NAME
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.Nm semget
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.Nd obtain a semaphore id
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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/sem.h
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.Ft int
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.Fn semget "key_t key" "int nsems" "int flag"
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.Sh DESCRIPTION
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Based on the values of
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.Fa key
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and
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.Fa flag ,
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.Fn semget
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returns the identifier of a newly created or previously existing
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set of semaphores.
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.\"
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.\" This is copied verbatim from the shmget manpage. Perhaps
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.\" it should go in a common manpage, such as .Xr ipc 2
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.\"
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The key
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is analogous to a filename: it provides a handle that names an
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IPC object.
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There are three ways to specify a key:
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.Bl -bullet
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.It
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IPC_PRIVATE may be specified, in which case a new IPC object
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will be created.
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.It
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An integer constant may be specified.
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If no IPC object corresponding
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to
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.Fa key
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is specified and the IPC_CREAT bit is set in
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.Fa flag ,
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a new one will be created.
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.It
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The
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.Xr ftok 3
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function
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may be used to generate a key from a pathname.
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.El
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.\"
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.\" Likewise for this section, except SHM_* becomes SEM_*.
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.\"
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.Pp
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The mode of a newly created IPC object is determined by
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.Em OR Ns 'ing
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the following constants into the
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.Fa flag
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argument:
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.Bl -tag -width XSEM_WXX6XXX
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.It Dv SEM_R
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Read access for user.
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.It Dv SEM_A
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Alter access for user.
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.It Dv ( SEM_R>>3 )
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Read access for group.
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.It Dv ( SEM_A>>3 )
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Alter access for group.
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.It Dv ( SEM_R>>6 )
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Read access for other.
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.It Dv ( SEM_A>>6 )
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Alter access for other.
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.El
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.Pp
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If a new set of semaphores is being created,
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.Fa nsems
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is used to indicate the number of semaphores the set should contain.
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Otherwise,
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.Fa nsems
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may be specified as 0.
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.Sh RETURN VALUES
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The
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.Fn semget
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system call
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returns the id of a semaphore set if successful; 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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.Sh ERRORS
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The
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.Fn semget
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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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.\" ipcperm could fail (we are opening to read and write, as it were)
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.It Bq Er EACCES
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Access permission failure.
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.\"
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.\" sysv_sem.c is quite explicit about these, so I'm pretty sure
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.\" this is accurate
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.\"
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.It Bq Er EEXIST
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IPC_CREAT and IPC_EXCL were specified, and a semaphore set
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corresponding to
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.Fa key
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already exists.
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.It Bq Er EINVAL
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The number of semaphores requested exceeds the system imposed maximum
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per set.
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.It Bq Er EINVAL
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A semaphore set corresponding to
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.Fa key
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already exists and contains fewer semaphores than
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.Fa nsems .
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.It Bq Er EINVAL
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A semaphore set corresponding to
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.Fa key
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does not exist and
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.Fa nsems
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is 0 or negative.
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.It Bq Er ENOSPC
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Insufficiently many semaphores are available.
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.It Bq Er ENOSPC
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The kernel could not allocate a
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.Fa "struct semid_ds" .
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.It Bq Er ENOENT
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No semaphore set was found corresponding to
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.Fa key ,
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and IPC_CREAT was not specified.
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.El
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.Sh SEE ALSO
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.Xr semctl 2 ,
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.Xr semop 2 ,
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.Xr ftok 3
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