blk-mq: allow the driver to pass in a queue mapping

This allows drivers specify their own queue mapping by overriding the
setup-time function that builds the mq_map.  This can be used for
example to build the map based on the MSI-X vector mapping provided
by the core interrupt layer for PCI devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f01379f..6737fd7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -104,6 +104,7 @@
 		bool);
 typedef void (busy_tag_iter_fn)(struct request *, void *, bool);
 typedef int (poll_fn)(struct blk_mq_hw_ctx *, unsigned int);
+typedef int (map_queues_fn)(struct blk_mq_tag_set *set);
 
 
 struct blk_mq_ops {
@@ -144,6 +145,8 @@
 	init_request_fn		*init_request;
 	exit_request_fn		*exit_request;
 	reinit_request_fn	*reinit_request;
+
+	map_queues_fn		*map_queues;
 };
 
 enum {