minix/lib/libc/sys/msgctl.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
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
2012-02-14 14:52:02 +01:00

199 lines
5.5 KiB
Groff

.\" $NetBSD: msgctl.2,v 1.15 2010/03/22 19:30:55 joerg 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 25, 1999
.Dt MSGCTL 2
.Os
.Sh NAME
.Nm msgctl
.Nd message control operations
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/msg.h
.Ft int
.Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
.Sh DESCRIPTION
The
.Fn msgctl
system call performs control operations on the message queue specified
by
.Fa msqid .
.Pp
Each message queue has a
.Sy msqid_ds
structure associated with it which contains the following members:
.Bd -literal
struct ipc_perm msg_perm; /* msg queue permission bits */
msgqnum_t msg_qnum; /* # of msgs in the queue */
msglen_t 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
.Pp
The
.Sy ipc_perm
structure used inside the
.Sy msgid_ds
structure is defined in
.In sys/ipc.h
and contains the following members:
.Bd -literal
uid_t cuid; /* creator user id */
gid_t cgid; /* creator group id */
uid_t uid; /* user id */
gid_t gid; /* group id */
mode_t mode; /* permission (lower 9 bits) */
.Ed
.Pp
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
.Pf ( Dv MSGMNB
from
.In 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
.Pp
The permission to read from or write to a message queue (see
.Xr msgsnd 2
and
.Xr msgrcv 2 )
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
.Dv IPC_SET
or
.Dv 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.
.Pp
An attempt was made to increase the value of
.Va msg_qbytes
through
.Dv IPC_SET ,
but the caller is not the super-user.
.It Bq Er EACCES
.Fa cmd
is
.Dv 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.
.Pp
.Fa cmd
is not a valid command.
.It Bq Er EFAULT
.Fa buf
specifies an invalid address.
.El
.Sh SEE ALSO
.Xr msgget 2 ,
.Xr msgrcv 2 ,
.Xr msgsnd 2
.Sh STANDARDS
The
.Nm
system call conforms to
.St -xsh5 .
.Sh HISTORY
Message queues appeared in the first release of
.At V .