mq_getattr will get status infomation and attributes of message queue. The result will return in mqstat argument. mq_getattr gets mq_flags value, which is set when message queue was opened and can be modified by mq_setattr calls. mq_getattr gets mq_maxmsg, mq_msgsize value, which will be returned when message queue was opened. mq_getattr gets mq_curmsgs value, which will be returned as the number of the message currently on the queue. mq_getattr will return 0 on success. mq_getattr shall return -1 and set errno to indicate the error. mq_getattr may fail with EBADF if the mqdes is not a valid message message queue descriptor.