2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
170 lines
5.1 KiB
Groff
170 lines
5.1 KiB
Groff
.\" $NetBSD: semop.2,v 1.17 2010/03/22 19:30:55 joerg Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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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.Dd November 3, 2005
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.Dt SEMOP 2
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.Os
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.Sh NAME
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.Nm semop
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.Nd semaphore operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/sem.h
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.Ft int
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.Fn semop "int semid" "struct sembuf *sops" "size_t nsops"
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.Sh DESCRIPTION
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.Fn semop
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provides a number of atomic operations on a set of semaphores.
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The semaphore set is specified by
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.Fa semid ,
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.Fa sops
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is an array of semaphore operations, and
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.Fa nsops
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is the number of operations in this array.
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The
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.Va sembuf
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structures in the array contain the following members:
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.Bd -literal
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unsigned short sem_num; /* semaphore # */
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short sem_op; /* semaphore operation */
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short sem_flg; /* operation flags */
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.Ed
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.Pp
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Each operation (specified in
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.Va sem_op )
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is applied to semaphore number
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.Va sem_num
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in the set of semaphores specified by
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.Fa semid .
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The value of
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.Va sem_op
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determines the action taken in the following way:
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.Bl -bullet
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.It
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.Va sem_op
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is less than 0.
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The current process is blocked until the value of the
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semaphore is greater than or equal to the absolute value of
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.Va sem_op .
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The absolute value of
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.Va sem_op
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is then subtracted from the value of the semaphore, and the calling
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process continues.
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Negative values of
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.Va sem_op
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are thus used to enter critical regions.
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.It
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.Va sem_op
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is greater than 0.
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Its value is added to the value of the specified semaphore.
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This is used to leave critical regions.
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.It
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.Va sem_op
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is equal to 0.
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The calling process is blocked until the value of the
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specified semaphore reaches 0.
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.El
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.Pp
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The behaviour of each operation is influenced by the flags set in
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.Va sem_flg
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in the following way:
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.Bl -tag -width IPC_NOWAITX
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.It Dv IPC_NOWAIT
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In the case where the calling process would normally block, waiting
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for a semaphore to reach a certain value,
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.Dv IPC_NOWAIT
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makes the
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call return immediately, returning a value of \-1 and setting
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.Va errno
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to
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.Er EAGAIN .
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.It SEM_UNDO
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Keep track of the changes that this call makes to the value of a semaphore,
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so that they can be undone when the calling process terminates.
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This is useful to prevent other processes waiting on a semaphore to block
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forever, should the process that has the semaphore locked terminate in a
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critical section.
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.El
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.Sh RETURN VALUES
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Upon successful completion, a value of 0 is returned.
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Otherwise, \-1 is returned and the global variable
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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 semop
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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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There is no semaphore associated with
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.Fa semid .
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.It Bq Er EIDRM
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The semaphore set was removed while the process was waiting for one of
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its semaphores to reach a certain value.
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.It Bq Er EACCES
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The calling process has no permission to access the specified semaphore set.
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.It Bq Er E2BIG
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The value of
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.Fa nsops
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is too big.
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The maximum is defined as
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.Dv MAX_SOPS
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in
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.In sys/sem.h .
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.It Bq Er EFBIG
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.Va sem_num
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in one of the sem_buf structures is less than 0, or greater than the actual
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number of semaphores in the set specified by
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.Fa semid .
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.It Bq Er ENOSPC
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.Dv SEM_UNDO
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was requested, and there is not enough space left in the kernel to
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store the undo information.
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.It Bq Er EAGAIN
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The requested operation can not immediately be performed, and
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.Dv IPC_NOWAIT
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was set in
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.Va sem_flg .
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.It Bq Er EFAULT
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.Fa sops
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points to an illegal address.
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.El
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.Sh SEE ALSO
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.Xr semctl 2 ,
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.Xr semget 2
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Semaphores appeared in the first release of
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.At V .
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