mq_getattr(3c)

NAME
     mq_getattr - get attributes of a message queue

C SYNOPSIS
     #include <mqueue.h>

     int mq_getattr (mqd_t mqd, struct mq_attr *mqstat);

DESCRIPTION
     mq_getattr saves the attributes and status information of the message
     queue named by mqd into the mq_attr structure at address mqstat.  The
     following fields of the mq_attr structure are updated after a successful
     call to mq_getattr:

        long mq_flags;        /* message queue flags */
        long mq_maxmsg;       /* maximum number of messages */
        long mq_msgsize;      /* maximum size of a message*/
        long mq_curmsgs;      /* number of messages currently on queue */

     The fields have the following meanings:

     mq_flags  The set of flags which may be applied to the message queue on a
               queue descriptor mqd basis, rather than to the queue itself.
               The following flags are supported:

               O_NONBLOCK If set, mq_send and mq_receive operations on the
               queue named by mqd will not block when the queue is full or
               empty, respectively.

     mq_maxmsg The maximum number of messages that can be queued at any one
               time.  mq_send will fail, if O_NONBLOCK flag is set, or block
               after this many messages are queued. This attribute of the
               queue can be set only at time of queue creation.

     mq_msgsize
               The maximum size of a message that can be sent to or received
               from the queue.  This attribute of the queue can be set only at
               the time of queue creation.

     mq_curmsgs
               The number of messages currently on the message queue. This
               attribute can only be queried and cannot be explicitly set.

     mq_getattr will fail if one or more of the following conditions are true:

     [EBADF]        The message queue descriptor, mqd, is not valid.

     [EINTR]        A signal interrupted the mq_getattr function call.
SEE ALSO
     mq_open(3c), intro(3c), mq_unlink(3c), mq_receive(3c), mq_send(3c),
     mq_setattr(3c), mq_notify(3c)

DIAGNOSTICS
     Upon successful completion, a value of 0 is returned and the attributes
     of the queue are written into the mq_attr structure pointed to by mqstat.
     Otherwise, a value of -1 is returned and errno is set to indicate the
     error.