NAME
msgctl - XSI message control operations
SYNOPSIS
#include <sys/msg.h>
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
DESCRIPTION
The msgctl() function operates on XSI message queues (see the Base
Definitions volume of IEEE Std 1003.1-2001, Section 3.224, Message
Queue). It is unspecified whether this function interoperates with the
realtime interprocess communication facilities defined in Realtime .
The msgctl() function shall provide message control operations as
specified by cmd. The following values for cmd, and the message control
operations they specify, are:
IPC_STAT
Place the current value of each member of the msqid_ds data
structure associated with msqid into the structure pointed to by
buf. The contents of this structure are defined in <sys/msg.h>.
IPC_SET
Set the value of the following members of the msqid_ds 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
msg_qbytes
IPC_SET can only be executed by a process with appropriate privileges
or that has an effective user ID equal to the value of msg_perm.cuid or
msg_perm.uid in the msqid_ds data structure associated with msqid. Only
a process with appropriate privileges can raise the value of
msg_qbytes.
IPC_RMID
Remove the message queue identifier specified by msqid from the
system and destroy the message queue and msqid_ds data structure
associated with it. IPC_RMD can only be executed by a process
with appropriate privileges or one that has an effective user ID
equal to the value of msg_perm.cuid or msg_perm.uid in the
msqid_ds data structure associated with msqid.
RETURN VALUE
Upon successful completion, msgctl() shall return 0; otherwise, it
shall return -1 and set errno to indicate the error.
ERRORS
The msgctl() function shall fail if:
EACCES The argument cmd is IPC_STAT and the calling process does not
have read permission; see XSI Interprocess Communication .
EINVAL The value of msqid is not a valid message queue identifier; or
the value of cmd is not a valid command.
EPERM The argument cmd is IPC_RMID or IPC_SET and the effective user
ID of the calling process is not equal to that of a process with
appropriate privileges and it is not equal to the value of
msg_perm.cuid or msg_perm.uid in the data structure associated
with msqid.
EPERM The argument cmd is IPC_SET, an attempt is being made to
increase to the value of msg_qbytes, and the effective user ID
of the calling process does not have appropriate privileges.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The POSIX Realtime Extension defines alternative interfaces for
interprocess communication (IPC). Application developers who need to
use IPC should design their applications so that modules using the IPC
routines described in XSI Interprocess Communication can be easily
modified to use the alternative interfaces.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
XSI Interprocess Communication , Realtime , mq_close() , mq_getattr() ,
mq_notify() , mq_open() , mq_receive() , mq_send() , mq_setattr() ,
mq_unlink() , msgget() , msgrcv() , msgsnd() , the Base Definitions
volume of IEEE Std 1003.1-2001, <sys/msg.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .