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Diffstat (limited to 'lib/libc/gen/msgctl.3')
| -rw-r--r-- | lib/libc/gen/msgctl.3 | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/lib/libc/gen/msgctl.3 b/lib/libc/gen/msgctl.3 new file mode 100644 index 0000000..7978725 --- /dev/null +++ b/lib/libc/gen/msgctl.3 @@ -0,0 +1,214 @@ +.\" $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. +.\" +.\" $FreeBSD$ +.\"/ +.Dd November 24, 1997 +.Dt MSGCTL 3 +.Os +.Sh NAME +.Nm msgctl +.Nd message control operations +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In sys/types.h +.In sys/ipc.h +.In 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 . +.Pp +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 +.In sys/msg.h +and contains (amongst others) the following members: +.Bd -literal +struct msqid_ds { + struct ipc_perm msg_perm; /* msg queue permission bits */ + struct msg *msg_first; /* first message in the queue */ + struct msg *msg_last; /* last message in the queue */ + u_long msg_cbytes; /* number of bytes in use on the queue */ + u_long msg_qnum; /* number 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() */ + long msg_pad1; + time_t msg_rtime; /* time of last msgrcv() */ + long msg_pad2; + time_t msg_ctime; /* time of last msgctl() */ + long msg_pad3; + long msg_pad4[4]; +}; +.Ed +.Pp +The +.Vt ipc_perm +structure used inside the +.Vt msqid_ds +structure is defined in +.In 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 */ + ushort seq; /* sequence # (to generate unique msg/sem/shm id) */ + key_t key; /* user specified msg/sem/shm key */ +}; +.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 (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 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 +.Rv -std msgctl +.Sh ERRORS +The +.Fn msgctl +function +will fail if: +.Bl -tag -width Er +.It Bq Er EPERM +The +.Fa cmd +argument +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. +.Pp +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 EACCES +The command is IPC_STAT +and the caller has no read permission for this message queue. +.It Bq Er EINVAL +The +.Fa msqid +argument +is not a valid message queue identifier. +.Pp +.Va cmd +is not a valid command. +.It Bq Er EFAULT +The +.Fa buf +argument +specifies an invalid address. +.El +.Sh SEE ALSO +.Xr msgget 3 , +.Xr msgrcv 3 , +.Xr msgsnd 3 +.Sh HISTORY +Message queues appeared in the first release of +.At V . |
