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

NAME

       mq_getattr, mq_setattr - get/set message queue attributes

SYNOPSIS

       #include <mqueue.h>

       mqd_t mq_getattr(mqd_t mqdes, struct mq_attr *attr);

       mqd_t 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_overview(7)

COLOPHON

       This page is part of release 3.25 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								    2008-09-29							     MQ_GETATTR(3)