202 lines
5.8 KiB
Groff
202 lines
5.8 KiB
Groff
.\" $NetBSD: msgctl.2,v 1.1 1995/10/16 23:49:15 jtc 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 MSGCTL 3
|
|
.Os NetBSD
|
|
.Sh NAME
|
|
.Nm msgctl
|
|
.Nd message control operations
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/types.h>
|
|
.Fd #include <sys/ipc.h>
|
|
.Fd #include <sys/msg.h>
|
|
.Ft int
|
|
.Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn msgctl
|
|
system call performs some control operations on the message queue specified
|
|
by
|
|
.Fa msqid .
|
|
|
|
Each message queue has a data structure associated with it, parts of which
|
|
may be altered by
|
|
.Fn msgctl
|
|
and parts of which determine the actions of
|
|
.Fn msgctl .
|
|
The data structure is defined in
|
|
.Aq Pa sys/msg.h
|
|
and contains (amongst others) the following members:
|
|
.Bd -literal
|
|
struct msqid_ds {
|
|
struct ipc_perm msg_perm; /* msg queue permission bits */
|
|
u_long msg_cbytes; /* # of bytes in use on the queue */
|
|
u_long msg_qnum; /* # of msgs in the queue */
|
|
u_long msg_qbytes; /* max # of bytes on the queue */
|
|
pid_t msg_lspid; /* pid of last msgsnd() */
|
|
pid_t msg_lrpid; /* pid of last msgrcv() */
|
|
time_t msg_stime; /* time of last msgsnd() */
|
|
time_t msg_rtime; /* time of last msgrcv() */
|
|
time_t msg_ctime; /* time of last msgctl() */
|
|
};
|
|
.Ed
|
|
|
|
The
|
|
.Bf -literal
|
|
ipc_perm
|
|
.Ef
|
|
structure used inside the
|
|
.Bf -literal
|
|
shmid_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; /* permission (9 bits, see chmod(2)) */
|
|
ushort seq; /* sequence # (to generate unique id) */
|
|
key_t key; /* user specified msg/sem/shm key */
|
|
};
|
|
.Ed
|
|
|
|
The operation to be performed by
|
|
.Fn msgctl
|
|
is specified in
|
|
.Fa cmd
|
|
and is one of:
|
|
.Bl -tag -width IPC_RMIDX
|
|
.It Dv IPC_STAT
|
|
Gather information about the message queue and place it in the
|
|
structure pointed to by
|
|
.Fa buf .
|
|
.It Dv IPC_SET
|
|
Set the value of the
|
|
.Va msg_perm.uid ,
|
|
.Va msg_perm.gid ,
|
|
.Va msg_perm.mode
|
|
and
|
|
.Va msg_qbytes
|
|
fields in the structure associated with
|
|
.Fa msqid .
|
|
The values are taken from the corresponding fields in the structure
|
|
pointed to by
|
|
.Fa buf .
|
|
This operation can only be executed by the super-user, or a process that
|
|
has an effective user id equal to either
|
|
.Va msg_perm.cuid
|
|
or
|
|
.Va msg_perm.uid
|
|
in the data structure associated with the message queue.
|
|
The value of
|
|
.Va msg_qbytes
|
|
can only be increased by the super-user. Values for
|
|
.Va msg_qbytes
|
|
that exceed the system limit (MSGMNB from
|
|
.Aq Pa sys/msg.h )
|
|
are silently truncated to that limit.
|
|
|
|
.It Dv IPC_RMID
|
|
Remove the message queue specified by
|
|
.Fa msqid
|
|
and destroy the data associated with it. Only the super-user or a process
|
|
with an effective uid equal to the
|
|
.Va msg_perm.cuid
|
|
or
|
|
.Va msg_perm.uid
|
|
values in the data structure associated with the queue can do this.
|
|
.El
|
|
|
|
The permission to read from or write to a message queue (see
|
|
.Xr msgsnd 3
|
|
and
|
|
.Xr msgrcv 3 )
|
|
is determined by the
|
|
.Va msg_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 msg_perm.cuid
|
|
field or the
|
|
.Va msg_perm.uid
|
|
field, and the
|
|
effective gid can match either
|
|
.Va msg_perm.cgid
|
|
or
|
|
.Va msg_perm.gid .
|
|
.Sh RETURN VALUES
|
|
Upon successful completion, a value of 0 is returned. Otherwise, -1 is
|
|
returned and the global variable
|
|
.Va errno
|
|
is set to indicate the error.
|
|
.Sh ERRORS
|
|
.Fn msgctl
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EPERM
|
|
.Fa cmd
|
|
is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does
|
|
the effective uid match either the
|
|
.Va msg_perm.uid
|
|
or
|
|
.Va msg_perm.cuid
|
|
fields of the data structure associated with the message queue.
|
|
|
|
An attempt is made to increase the value of
|
|
.Va msg_qbytes
|
|
through IPC_SET
|
|
but the caller is not the super-user.
|
|
.It Bq Er EACCESS
|
|
The command is IPC_STAT
|
|
and the caller has no read permission for this message queue.
|
|
.It Bq Er EINVAL
|
|
.Fa msqid
|
|
is not a valid message queue identifier.
|
|
|
|
.Va cmd
|
|
is not a valid command.
|
|
.It Bq Er EFAULT
|
|
.Fa buf
|
|
specifies an invalid address.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr msgsnd 3 ,
|
|
.Xr msgrcv 3 ,
|
|
.Xr msgget 3
|
|
.Sh HISTORY
|
|
Message queues appeared in the first release of AT&T Unix System V.
|