msgctl(S)
msgctl --
message control operations
Syntax
cc ... -lc
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgctl (msqid, cmd, buf)
int msqid, cmd;
struct msqid_ds *buf;
Description
The
msgctl
system call
provides a variety of message control operations as specified by
cmd.
The following
cmds
are available:
IPC_RMID-
Remove the message queue identifier specified by
msqid
from the system and destroy the message queue and data structure
associated with it.
This cmd can only be executed by a process that has an effective user
ID
equal to either that of super user, or to the value of
msg_perm.cuid
or
msg_perm.uid
in the data structure associated with
msqid.
IPC_SET-
Set the value of the following members of the data structure associated with
msqid
to the corresponding value found in the structure pointed to by
buf:
msg_perm.uid
msg_perm.gid
msg_perm.mode /* only low 9 bits */
msg_qbytes
This cmd can only be executed by a process that
has an effective user ID
equal to either
that of super user,
or to the value of
msg_perm.cuid
or
msg_perm.uid
in the data structure associated with
msqid.
Only super user can raise the value of
msg_qbytes.
IPC_STAT-
Place the current value of each member of the data structure
associated with
msqid
into the structure pointed to by
buf.
The contents of this structure are defined in
Intro(S).
The
msgctl
system call
fails if one or more of the following is true:
[EACCES]-
The
cmd
argument
is equal to
IPC_STAT
and
{READ}
operation permission is denied to the calling process.
[EFAULT]-
The
buf
argument
points to an illegal address.
[EINVAL]-
1. The msqid argument is not a valid message queue identifier.
2. The cmd argument is not a valid command.
[EPERM]-
1. The cmd argument is equal to IPC_RMID
or IPC_SET. The effective user ID
of the calling process is not equal to that of super user,
or to the value of
msg_perm.cuid or
msg_perm.uid in the data structure associated with
msqid.
2. The cmd argument is equal to IPC_SET,
an attempt is being made to increase to the value of
msg_qbytes, and the effective user ID
of the calling process is not equal to that of super user.
Diagnostics
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned, and
errno
is set to indicate the error.
See also
Intro(S),
msgget(S),
msgop(S)
Standards conformance
msgctl is conformant with:
X/Open Portability Guide, Issue 3, 1989
.
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003