Originální popis anglicky:
msgctl - XSI message control operations
Návod, kniha: POSIX Programmer's Manual
#include <sys/msg.h>
int msgctl(int
msqid, int
cmd, struct msqid_ds
*buf);
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.
Upon successful completion,
msgctl() shall return 0; otherwise, it shall
return -1 and set
errno to indicate the error.
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.
None.
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.
None.
None.
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>
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
.
