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Linux 2.6 - man page for mq_setattr (linux section 3)

MQ_GETATTR(3)			    Linux Programmer's Manual			    MQ_GETATTR(3)

NAME
       mq_getattr, mq_setattr - get/set message queue attributes

SYNOPSIS
       #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.

DESCRIPTION
       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().

RETURN VALUE
       On success mq_getattr() and mq_setattr() return 0; on error, -1 is  returned,  with  errno
       set to indicate the error.

ERRORS
       EBADF  The descriptor specified in mqdes is invalid.

       EINVAL newattr->mq_flags contained set bits other than O_NONBLOCK.

CONFORMING TO
       POSIX.1-2001.

NOTES
       On  Linux,  mq_getattr()  and  mq_setattr()  are  library  functions layered on top of the
       mq_getsetattr(2) system call.

SEE ALSO
       mq_close(3), mq_notify(3), mq_open(3), mq_receive(3), mq_send(3),  mq_unlink(3),  mq_over-
       view(7)

COLOPHON
       This  page  is  part of release 3.55 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)


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