1 .\" $NetBSD: msgctl.2,v 1.1 1995/10/16 23:49:15 jtc Exp $
3 .\" Copyright (c) 1995 Frank van der Linden
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17 .\" by Frank van der Linden
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32 .\" $FreeBSD: src/lib/libc/gen/msgctl.3,v 1.8.2.7 2003/03/13 18:05:37 trhodes Exp $
33 .\" $DragonFly: src/lib/libc/gen/msgctl.3,v 1.3 2006/05/26 19:39:36 swildner Exp $
40 .Nd message control operations
48 .Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
52 system call performs some control operations on the message queue specified
56 Each message queue has a data structure associated with it, parts of which
59 and parts of which determine the actions of
61 The data structure is defined in
63 and contains (amongst others) the following members:
66 struct ipc_perm msg_perm; /* msg queue permission bits */
67 struct msg *msg_first; /* first message in the queue */
68 struct msg *msg_last; /* last message in the queue */
69 u_long msg_cbytes; /* number of bytes in use on the queue */
70 u_long msg_qnum; /* number of msgs in the queue */
71 u_long msg_qbytes; /* max # of bytes on the queue */
72 pid_t msg_lspid; /* pid of last msgsnd() */
73 pid_t msg_lrpid; /* pid of last msgrcv() */
74 time_t msg_stime; /* time of last msgsnd() */
76 time_t msg_rtime; /* time of last msgrcv() */
78 time_t msg_ctime; /* time of last msgctl() */
86 structure used inside the
88 structure is defined in
93 ushort cuid; /* creator user id */
94 ushort cgid; /* creator group id */
95 ushort uid; /* user id */
96 ushort gid; /* group id */
97 ushort mode; /* r/w permission */
98 ushort seq; /* sequence # (to generate unique msg/sem/shm id) */
99 key_t key; /* user specified msg/sem/shm key */
103 The operation to be performed by
108 .Bl -tag -width IPC_RMIDX
110 Gather information about the message queue and place it in the
111 structure pointed to by
120 fields in the structure associated with
122 The values are taken from the corresponding fields in the structure
125 This operation can only be executed by the super-user, or a process that
126 has an effective user id equal to either
130 in the data structure associated with the message queue.
133 can only be increased by the super-user.
136 that exceed the system limit (MSGMNB from
138 are silently truncated to that limit.
140 Remove the message queue specified by
142 and destroy the data associated with it.
143 Only the super-user or a process
144 with an effective uid equal to the
148 values in the data structure associated with the queue can do this.
151 The permission to read from or write to a message queue (see
157 field in the same way as is
160 but the effective uid can match either the
165 effective gid can match either
181 is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does
182 the effective uid match either the
186 fields of the data structure associated with the message queue.
188 An attempt is made to increase the value of
191 but the caller is not the super-user.
193 The command is IPC_STAT
194 and the caller has no read permission for this message queue.
199 is not a valid message queue identifier.
202 is not a valid command.
207 specifies an invalid address.
214 Message queues appeared in the first release of