gen/msgctl.3

   1 .\"     $NetBSD: msgctl.2,v 1.1 1995/10/16 23:49:15 jtc Exp $
   2 .\"
   3 .\" Copyright (c) 1995 Frank van der Linden
   4 .\" All rights reserved.
   5 .\"
   6 .\" Redistribution and use in source and binary forms, with or without
   7 .\" modification, are permitted provided that the following conditions
   8 .\" are met:
   9 .\" 1. Redistributions of source code must retain the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer.
  11 .\" 2. Redistributions in binary form must reproduce the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer in the
  13 .\"    documentation and/or other materials provided with the distribution.
  14 .\" 3. All advertising materials mentioning features or use of this software
  15 .\"    must display the following acknowledgement:
  16 .\"      This product includes software developed for the NetBSD Project
  17 .\"      by Frank van der Linden
  18 .\" 4. The name of the author may not be used to endorse or promote products
  19 .\"    derived from this software without specific prior written permission
  20 .\"
  21 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  22 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  23 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  24 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  25 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  26 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  27 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  28 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  29 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  30 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  31 .\"
  32 .\" $FreeBSD: src/lib/libc/gen/msgctl.3,v 1.16 2001/10/01 16:08:51 ru Exp $
  33 .\"/
  34 .Dd November 24, 1997
  35 .Dt MSGCTL 3
  36 .Os
  37 .Sh NAME
  38 .Nm msgctl
  39 .Nd message control operations
  40 .Sh LIBRARY
  41 .Lb libc
  42 .Sh SYNOPSIS
  43 .In sys/types.h
  44 .In sys/ipc.h
  45 .In sys/msg.h
  46 .Ft int
  47 .Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
  48 .Sh DESCRIPTION
  49 The
  50 .Fn msgctl
  51 system call performs some control operations on the message queue specified
  52 by
  53 .Fa msqid .
  54 .Pp
  55 Each message queue has a data structure associated with it, parts of which
  56 may be altered by
  57 .Fn msgctl
  58 and parts of which determine the actions of
  59 .Fn msgctl .
  60 The data structure is defined in
  61 .Aq Pa sys/msg.h
  62 and contains (amongst others) the following members:
  63 .Bd -literal
  64 struct msqid_ds {
  65         struct  ipc_perm msg_perm;      /* msg queue permission bits */
  66         struct  msg *msg_first; /* first message in the queue */
  67         struct  msg *msg_last;  /* last message in the queue */
  68         u_long  msg_cbytes;     /* number of bytes in use on the queue */
  69         u_long  msg_qnum;       /* number of msgs in the queue */
  70         u_long  msg_qbytes;     /* max # of bytes on the queue */
  71         pid_t   msg_lspid;      /* pid of last msgsnd() */
  72         pid_t   msg_lrpid;      /* pid of last msgrcv() */
  73         time_t  msg_stime;      /* time of last msgsnd() */
  74         long    msg_pad1;
  75         time_t  msg_rtime;      /* time of last msgrcv() */
  76         long    msg_pad2;
  77         time_t  msg_ctime;      /* time of last msgctl() */
  78         long    msg_pad3;
  79         long    msg_pad4[4];
  80 };
  81 .Ed
  82 .Pp
  83 The
  84 .Vt ipc_perm
  85 structure used inside the
  86 .Vt shmid_ds
  87 structure is defined in
  88 .Aq Pa sys/ipc.h
  89 and looks like this:
  90 .Bd -literal
  91 struct ipc_perm {
  92         ushort  cuid;   /* creator user id */
  93         ushort  cgid;   /* creator group id */
  94         ushort  uid;    /* user id */
  95         ushort  gid;    /* group id */
  96         ushort  mode;   /* r/w permission */
  97         ushort  seq;    /* sequence # (to generate unique msg/sem/shm id) */
  98         key_t   key;    /* user specified msg/sem/shm key */
  99 };
 100 .Ed
 101 .Pp
 102 The operation to be performed by
 103 .Fn msgctl
 104 is specified in
 105 .Fa cmd
 106 and is one of:
 107 .Bl -tag -width IPC_RMIDX
 108 .It Dv IPC_STAT
 109 Gather information about the message queue and place it in the
 110 structure pointed to by
 111 .Fa buf .
 112 .It Dv IPC_SET
 113 Set the value of the
 114 .Va msg_perm.uid ,
 115 .Va msg_perm.gid ,
 116 .Va msg_perm.mode
 117 and
 118 .Va msg_qbytes
 119 fields in the structure associated with
 120 .Fa msqid .
 121 The values are taken from the corresponding fields in the structure
 122 pointed to by
 123 .Fa buf .
 124 This operation can only be executed by the super-user, or a process that
 125 has an effective user id equal to either
 126 .Va msg_perm.cuid
 127 or
 128 .Va msg_perm.uid
 129 in the data structure associated with the message queue.
 130 The value of
 131 .Va msg_qbytes
 132 can only be increased by the super-user.
 133 Values for
 134 .Va msg_qbytes
 135 that exceed the system limit (MSGMNB from
 136 .Aq Pa sys/msg.h )
 137 are silently truncated to that limit.
 138 .It Dv IPC_RMID
 139 Remove the message queue specified by
 140 .Fa msqid
 141 and destroy the data associated with it.
 142 Only the super-user or a process
 143 with an effective uid equal to the
 144 .Va msg_perm.cuid
 145 or
 146 .Va msg_perm.uid
 147 values in the data structure associated with the queue can do this.
 148 .El
 149 .Pp
 150 The permission to read from or write to a message queue (see
 151 .Xr msgsnd 3
 152 and
 153 .Xr msgrcv 3 )
 154 is determined by the
 155 .Va msg_perm.mode
 156 field in the same way as is
 157 done with files (see
 158 .Xr chmod 2 ) ,
 159 but the effective uid can match either the
 160 .Va msg_perm.cuid
 161 field or the
 162 .Va msg_perm.uid
 163 field, and the
 164 effective gid can match either
 165 .Va msg_perm.cgid
 166 or
 167 .Va msg_perm.gid .
 168 .Sh RETURN VALUES
 169 .Rv -std msgctl
 170 .Sh ERRORS
 171 .Fn msgctl
 172 will fail if:
 173 .Bl -tag -width Er
 174 .It Bq Er EPERM
 175 .Fa cmd
 176 is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does
 177 the effective uid match either the
 178 .Va msg_perm.uid
 179 or
 180 .Va msg_perm.cuid
 181 fields of the data structure associated with the message queue.
 182 .Pp
 183 An attempt is made to increase the value of
 184 .Va msg_qbytes
 185 through IPC_SET
 186 but the caller is not the super-user.
 187 .It Bq Er EACCES
 188 The command is IPC_STAT
 189 and the caller has no read permission for this message queue.
 190 .It Bq Er EINVAL
 191 .Fa msqid
 192 is not a valid message queue identifier.
 193 .Pp
 194 .Va cmd
 195 is not a valid command.
 196 .It Bq Er EFAULT
 197 .Fa buf
 198 specifies an invalid address.
 199 .El
 200 .Sh SEE ALSO
 201 .Xr msgget 3 ,
 202 .Xr msgrcv 3 ,
 203 .Xr msgsnd 3
 204 .Sh HISTORY
 205 Message queues appeared in the first release of
 206 .At V .