227 lines
6.2 KiB
Groff
227 lines
6.2 KiB
Groff
.\" $NetBSD: semctl.2,v 1.4 1997/11/27 10:25:04 mikel Exp $
|
|
.\"
|
|
.\" Copyright (c) 1995 Frank van der Linden
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed for the NetBSD Project
|
|
.\" by Frank van der Linden
|
|
.\" 4. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd August 17, 1995
|
|
.Dt SEMCTL 2
|
|
.Os NetBSD
|
|
.Sh NAME
|
|
.Nm semctl
|
|
.Nd semaphore control operations
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/types.h>
|
|
.Fd #include <sys/ipc.h>
|
|
.Fd #include <sys/sem.h>
|
|
.Ft int
|
|
.Fn semctl "int semid" "int semnum" "int cmd" "union semun arg"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn semctl
|
|
system call provides a number of control operations on the semaphore specified
|
|
by
|
|
.Fa semnum
|
|
and
|
|
.Fa semid .
|
|
The operation to be performed is specified in
|
|
.Fa cmd
|
|
(see below).
|
|
.Fa arg
|
|
is a union of the following fields:
|
|
.Bd -literal
|
|
int val; /* value for SETVAL */
|
|
struct semid_ds *buf; /* buffer for IPC_{STAT,SET} */
|
|
u_short *array; /* array for GETALL & SETALL */
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Bf -literal
|
|
semid_ds
|
|
.Ef
|
|
structure used in the
|
|
.Dv IPC_SET
|
|
and
|
|
.Dv IPC_STAT
|
|
commands is defined as follows in
|
|
.Aq Pa sys/sem.h :
|
|
.Bd -literal
|
|
struct semid_ds {
|
|
struct ipc_perm sem_perm; /* operation permissions */
|
|
struct sem *sem_base; /* semaphore set */
|
|
u_short sem_nsems; /* number of sems in set */
|
|
time_t sem_otime; /* last operation time */
|
|
time_t sem_ctime; /* last change time */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Bf -literal
|
|
ipc_perm
|
|
.Ef
|
|
structure used inside the
|
|
.Bf -literal
|
|
semid_ds
|
|
.Ef
|
|
structure is defined in
|
|
.Aq Pa sys/ipc.h
|
|
and looks like this:
|
|
.Bd -literal
|
|
struct ipc_perm {
|
|
ushort cuid; /* creator user id */
|
|
ushort cgid; /* creator group id */
|
|
ushort uid; /* user id */
|
|
ushort gid; /* group id */
|
|
ushort mode; /* r/w permission (see chmod(2)) */
|
|
ushort seq; /* sequence # (to generate unique msg/sem/shm id) */
|
|
key_t key; /* user specified msg/sem/shm key */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
.Fn semctl
|
|
provides the following operations:
|
|
.Bl -tag -width IPC_RMIDX
|
|
.It Dv GETVAL
|
|
Return the value of the semaphore.
|
|
.It Dv SETVAL
|
|
Set the value of the semaphore to
|
|
.Fa arg.val .
|
|
.It Dv GETPID
|
|
Return the pid of the last process that did an operation on this semaphore.
|
|
.It Dv GETNCNT
|
|
Return the number of processes waiting to acquire the semaphore.
|
|
.It Dv GETZCNT
|
|
Return the number of processes waiting for the value of the semaphore to
|
|
reach 0.
|
|
.It Dv GETALL
|
|
Return the values of all the semaphores associated with
|
|
.Fa semid .
|
|
.It Dv SETALL
|
|
Set the values of all the semaphores that are associated with the semaphore
|
|
identifier
|
|
.Fa semid
|
|
to the corresponding values in
|
|
.Fa arg.array .
|
|
.It Dv IPC_STAT
|
|
Gather statistics about a semaphore and place the information in the
|
|
.Bf -literal
|
|
semid_ds
|
|
.Ef
|
|
structure pointed to by
|
|
.Fa arg.buf
|
|
(see above).
|
|
.It Dv IPC_SET
|
|
Set the value of the
|
|
.Va sem_perm.uid ,
|
|
.Va sem_perm.gid
|
|
and
|
|
.Va sem_perm.mode
|
|
fields in the structure associated with the semaphore.
|
|
The values are taken from the corresponding fields in the structure
|
|
pointed to by
|
|
.Fa arg.buf .
|
|
This operation can only be executed by the super-user, or a process that
|
|
has an effective user id equal to either
|
|
.Va sem_perm.cuid
|
|
or
|
|
.Va sem_perm.uid
|
|
in the data structure associated with the message queue.
|
|
.It Dv IPC_RMID
|
|
Remove the semaphores associated with
|
|
.Fa semid
|
|
from the system and destroy the data structures associated with it. Only the
|
|
super-user or a process with an effective uid equal to the
|
|
.Va sem_perm.cuid
|
|
or
|
|
.Va sem_perm.uid
|
|
values in the data structure associated with the semaphore can do this.
|
|
.El
|
|
.Pp
|
|
The permission to read or change a message queue (see
|
|
.Xr semop 2 )
|
|
is determined by the
|
|
.Va sem_perm.mode
|
|
field in the same way as is
|
|
done with files (see
|
|
.Xr chmod 2 ),
|
|
but the effective uid can match either the
|
|
.Va sem_perm.cuid
|
|
field or the
|
|
.Va sem_perm.uid
|
|
field, and the
|
|
effective gid can match either
|
|
.Va sem_perm.cgid
|
|
or
|
|
.Va sem_perm.gid .
|
|
.Sh RETURN VALUES
|
|
For the
|
|
.Dv GETVAL ,
|
|
.Dv GETPID ,
|
|
.Dv GETNCNT ,
|
|
and
|
|
.Dv GETZCNT
|
|
operations,
|
|
.Fn semctl
|
|
returns one of the values described above if successful. All other operations
|
|
will make
|
|
.Fn semctl
|
|
return 0 if no errors occur. Otherwise -1 is returned and
|
|
.Va errno
|
|
set to reflect the error.
|
|
.Sh ERRORS
|
|
.Fn semctl
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EPERM
|
|
.Fa cmd
|
|
is equal to
|
|
.Dv IPC_SET
|
|
or
|
|
.Dv IPC_RMID
|
|
and the caller is not the super-user, nor does
|
|
the effective uid match either the
|
|
.Va sem_perm.uid
|
|
or
|
|
.Va sem_perm.cuid
|
|
fields of the data structure associated with the message queue.
|
|
.It Bq Er EACCES
|
|
The caller has no operation permission for this semaphore.
|
|
.It Bq Er EINVAL
|
|
.Fa semid
|
|
is not a valid message semaphore identifier.
|
|
.Pp
|
|
.Va cmd
|
|
is not a valid command.
|
|
.It Bq Er EFAULT
|
|
.Fa arg.buf
|
|
specifies an invalid address.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr semget 2 ,
|
|
.Xr semop 2
|