_mqueue_recv
error = _mqueue_recv(mq, &msg, -1);
error = _mqueue_recv(mq, &msg, 0);
error = _mqueue_recv(mq, &msg, -1);
error = _mqueue_recv(mq, &msg, tvtohz(&tv));
static int _mqueue_recv(struct mqueue *mq, struct mqueue_msg **msg,