blk-mq: initial support for multiple queue maps

Add a queue offset to the tag map. This enables users to map
iteratively, for each queue map type they support.

Bump maximum number of supported maps to 2, we're now fully
able to support more than 1 map.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-cpumap.c

@@ -14,9 +14,10 @@
 #include "blk.h"
 #include "blk-mq.h"
 
-static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
+static int cpu_to_queue_index(struct blk_mq_queue_map *qmap,
+			      unsigned int nr_queues, const int cpu)
 {
-	return cpu % nr_queues;
+	return qmap->queue_offset + (cpu % nr_queues);
 }
 
 static int get_first_sibling(unsigned int cpu)
@@ -44,11 +45,11 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 		 * performace optimizations.
 		 */
 		if (cpu < nr_queues) {
-			map[cpu] = cpu_to_queue_index(nr_queues, cpu);
+			map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
 		} else {
 			first_sibling = get_first_sibling(cpu);
 			if (first_sibling == cpu)
-				map[cpu] = cpu_to_queue_index(nr_queues, cpu);
+				map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
 			else
 				map[cpu] = map[first_sibling];
 		}

block/blk-mq-pci.c

@@ -43,7 +43,7 @@ int blk_mq_pci_map_queues(struct blk_mq_queue_map *qmap, struct pci_dev *pdev,
 			goto fallback;
 
 		for_each_cpu(cpu, mask)
-			qmap->mq_map[cpu] = queue;
+			qmap->mq_map[cpu] = qmap->queue_offset + queue;
 	}
 
 	return 0;

block/blk-mq-virtio.c

@@ -44,7 +44,7 @@ int blk_mq_virtio_map_queues(struct blk_mq_queue_map *qmap,
 			goto fallback;
 
 		for_each_cpu(cpu, mask)
-			qmap->mq_map[cpu] = queue;
+			qmap->mq_map[cpu] = qmap->queue_offset + queue;
 	}
 
 	return 0;

include/linux/blk-mq.h

@@ -78,10 +78,11 @@ struct blk_mq_hw_ctx {
 struct blk_mq_queue_map {
 	unsigned int *mq_map;
 	unsigned int nr_queues;
+	unsigned int queue_offset;
 };
 
 enum {
-	HCTX_MAX_TYPES = 1,
+	HCTX_MAX_TYPES = 2,
 };
 
 struct blk_mq_tag_set {