blk-mq-debugfs: support rq_qos

blk-mq-debugfs has been proved as very helpful for debug some
tough issues, such as IO hang.

We have seen blk-wbt related IO hang several times, even inside
Red Hat BZ, there is such report not sovled yet, so this patch
adds support debugfs on rq_qos.

Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
index a9160be..8c9012a 100644
--- a/block/blk-mq-debugfs.h
+++ b/block/blk-mq-debugfs.h
@@ -31,6 +31,10 @@ void blk_mq_debugfs_unregister_sched(struct request_queue *q);
 int blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
 				       struct blk_mq_hw_ctx *hctx);
 void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
+
+int blk_mq_debugfs_register_rqos(struct rq_qos *rqos);
+void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos);
+void blk_mq_debugfs_unregister_queue_rqos(struct request_queue *q);
 #else
 static inline int blk_mq_debugfs_register(struct request_queue *q)
 {
@@ -78,6 +82,19 @@ static inline int blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
 static inline void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx)
 {
 }
+
+static inline int blk_mq_debugfs_register_rqos(struct rq_qos *rqos)
+{
+	return 0;
+}
+
+static inline void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos)
+{
+}
+
+static inline void blk_mq_debugfs_unregister_queue_rqos(struct request_queue *q)
+{
+}
 #endif
 
 #ifdef CONFIG_BLK_DEBUG_FS_ZONED