int hpsb_get_tlabel (struct hpsb_packet * packet, int wait);
Every asynchronous transaction on the 1394 bus needs a transaction label to match the response to the request. This label has to be different from any other transaction label in an outstanding request to the same node to make matching possible without ambiguity.
There are 64 different tlabels, so an allocated tlabel has to be freed with hpsb_free_tlabel after the transaction is complete (unless it's reused again for the same target node).
wait cannot be set if in_interrupt
Zero on success, otherwise non-zero. A non-zero return generally means there are no available tlabels.