| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
MQ_GETATTR(3) Linux Programmer's Manual MQ_GETATTR(3)
mq_getattr, mq_setattr - get/set message queue attributes
#include <mqueue.h>
int mq_getattr(mqd_t mqdes, struct mq_attr *attr);
int mq_setattr(mqd_t mqdes, struct mq_attr *newattr,
struct mq_attr *oldattr);
Link with -lrt.
mq_getattr() and mq_setattr() respectively retrieve and modify attributes of
the message queue referred to by the descriptor mqdes.
mq_getattr() returns an mq_attr structure in the buffer pointed by attr. This
structure is defined as:
struct mq_attr {
long mq_flags; /* Flags: 0 or O_NONBLOCK */
long mq_maxmsg; /* Max. # of messages on queue */
long mq_msgsize; /* Max. message size (bytes) */
long mq_curmsgs; /* # of messages currently in queue */
};
The mq_flags field contains flags associated with the open message queue
description. This field is initialized when the queue is created by
mq_open(3). The only flag that can appear in this field is O_NONBLOCK.
The mq_maxmsg and mq_msgsize fields are set when the message queue is created
by mq_open(3). The mq_maxmsg field is an upper limit on the number of
messages that may be placed on the queue using mq_send(3). The mq_msgsize
field is an upper limit on the size of messages that may be placed on the
queue. Both of these fields must have a value greater than zero. Two /proc
files that place ceilings on the values for these fields are described in
mq_open(3).
The mq_curmsgs field returns the number of messages currently held in the
queue.
mq_setattr() sets message queue attributes using information supplied in the
mq_attr structure pointed to by newattr. The only attribute that can be
modified is the setting of the O_NONBLOCK flag in mq_flags. The other fields
in newattr are ignored. If the oldattr field is not NULL, then the buffer
that it points to is used to return an mq_attr structure that contains the
same information that is returned by mq_getattr().
On success mq_getattr() and mq_setattr() return 0; on error, -1 is returned,
with errno set to indicate the error.
EBADF The descriptor specified in mqdes is invalid.
EINVAL newattr->mq_flags contained set bits other than O_NONBLOCK.
POSIX.1-2001.
On Linux, mq_getattr() and mq_setattr() are library functions layered on top
of the mq_getsetattr(2) system call.
mq_close(3), mq_notify(3), mq_open(3), mq_receive(3), mq_send(3),
mq_unlink(3), mq_overview(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-08-29 MQ_GETATTR(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface