HP-UX Reference (11i v2 03/08) - 2 System Calls (vol 5)

m
msgctl(2) msgctl(2)
NAME
msgctl - message control operations
SYNOPSIS
#include <sys/msg.h>
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
DESCRIPTION
msgctl() provides a variety of message control operations as specified by cmd. The following cmds are
available:
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
glossary (9).
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 either
msg_perm.uid or
msg_perm.cuid in the data structure associated with msqid . Only super-user
can raise the value of msg_qbytes.
WARNING: Programs compiled on HP-UX revisions prior to 11.11 use old 16-bit
msqid_ds structure fields (obtained via
IPC_STAT) which can describe queue sizes
only up to 64KBytes. Care must be taken such that queues shared with such pro-
grams are not made larger than 64KBytes (65535). Or, those existing programs
should be recompiled. Or, the system administrator should restrict the
MSGMNB
kernel tunable parameter to 64KBytes or less.
IPC_RMID Remove the message queue identifier specified by msqid from the system and des-
troy 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 either msg_perm.uid or msg_perm.cuid
in the data struc-
ture associated with msqid.
RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of −1 is returned and
errno is
set to indicate the error.
ERRORS
msgctl() fails if one or more of the following is true:
[EINVAL] msqid is not a valid message queue identifier.
[EINVAL] cmd is not a valid command, or the command contains invalid parameters.
[EACCES] cmd is equal to IPC_STAT and Read operation permission is denied to the calling pro-
cess (see message operation permissions in glossary (9)).
[EPERM] cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process
is not equal to that of a user who has appropriate privileges and it is not equal to the
value of either msg_perm.uid or msg_perm.cuid in the data structure associated
with msqid.
[EPERM] cmd 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.
[EFAULT] buf points to an illegal address. Reliable detection of this error is implementation depen-
dent.
HP-UX 11i Version 2: August 2003 − 1 − Hewlett-Packard Company Section 2−−189