1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
138 lines
3.8 KiB
Groff
138 lines
3.8 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 September 12, 1995
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.Dt SEMGET 2
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.Os FreeBSD
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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 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 "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. 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. 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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.Fn ftok
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may be used to generate a key from a pathname. See
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.Xr ftok 3 .
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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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parameter:
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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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.Fn Semget
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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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.Fn Semget
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will fail if:
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.Bl -tag -width Er
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.\" ipcperm could fail (we're 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 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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.Sh SEE ALSO
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.Xr semctl 2 ,
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.Xr semop 2
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