blk-mq: factor out a blk_mq_alloc_sq_tag_set helper

Factour out a helper to initialize a simple single hw queue tag_set from
blk_mq_init_sq_queue.  This will allow to phase out blk_mq_init_sq_queue
in favor of a more symmetric and general API.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210602065345.355274-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -3152,24 +3152,12 @@ struct request_queue *blk_mq_init_sq_queue(struct blk_mq_tag_set *set,
 	struct request_queue *q;
 	int ret;
 
-	memset(set, 0, sizeof(*set));
-	set->ops = ops;
-	set->nr_hw_queues = 1;
-	set->nr_maps = 1;
-	set->queue_depth = queue_depth;
-	set->numa_node = NUMA_NO_NODE;
-	set->flags = set_flags;
-
-	ret = blk_mq_alloc_tag_set(set);
+	ret = blk_mq_alloc_sq_tag_set(set, ops, queue_depth, set_flags);
 	if (ret)
 		return ERR_PTR(ret);
-
 	q = blk_mq_init_queue(set);
-	if (IS_ERR(q)) {
+	if (IS_ERR(q))
 		blk_mq_free_tag_set(set);
-		return q;
-	}
-
 	return q;
 }
 EXPORT_SYMBOL(blk_mq_init_sq_queue);
@@ -3589,6 +3577,22 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 }
 EXPORT_SYMBOL(blk_mq_alloc_tag_set);
 
+/* allocate and initialize a tagset for a simple single-queue device */
+int blk_mq_alloc_sq_tag_set(struct blk_mq_tag_set *set,
+		const struct blk_mq_ops *ops, unsigned int queue_depth,
+		unsigned int set_flags)
+{
+	memset(set, 0, sizeof(*set));
+	set->ops = ops;
+	set->nr_hw_queues = 1;
+	set->nr_maps = 1;
+	set->queue_depth = queue_depth;
+	set->numa_node = NUMA_NO_NODE;
+	set->flags = set_flags;
+	return blk_mq_alloc_tag_set(set);
+}
+EXPORT_SYMBOL_GPL(blk_mq_alloc_sq_tag_set);
+
 void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 {
 	int i, j;

include/linux/blk-mq.h

@@ -439,6 +439,9 @@ struct request_queue *blk_mq_init_sq_queue(struct blk_mq_tag_set *set,
 void blk_mq_unregister_dev(struct device *, struct request_queue *);
 
 int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set);
+int blk_mq_alloc_sq_tag_set(struct blk_mq_tag_set *set,
+		const struct blk_mq_ops *ops, unsigned int queue_depth,
+		unsigned int set_flags);
 void blk_mq_free_tag_set(struct blk_mq_tag_set *set);
 
 void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule);