block/rq_qos: add rq_qos_merge()

Add a merge hook for rq_qos.  This will be used by io.weight.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -604,6 +604,7 @@ bool bio_attempt_back_merge(struct request *req, struct bio *bio,
 		return false;
 
 	trace_block_bio_backmerge(req->q, req, bio);
+	rq_qos_merge(req->q, req, bio);
 
 	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
 		blk_rq_set_mixed_merge(req);
@@ -625,6 +626,7 @@ bool bio_attempt_front_merge(struct request *req, struct bio *bio,
 		return false;
 
 	trace_block_bio_frontmerge(req->q, req, bio);
+	rq_qos_merge(req->q, req, bio);
 
 	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
 		blk_rq_set_mixed_merge(req);
@@ -650,6 +652,8 @@ bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
 	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 		goto no_merge;
 
+	rq_qos_merge(q, req, bio);
+
 	req->biotail->bi_next = bio;
 	req->biotail = bio;
 	req->__data_len += bio->bi_iter.bi_size;

block/blk-rq-qos.c

@@ -83,6 +83,15 @@ void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
 	} while (rqos);
 }
 
+void __rq_qos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio)
+{
+	do {
+		if (rqos->ops->merge)
+			rqos->ops->merge(rqos, rq, bio);
+		rqos = rqos->next;
+	} while (rqos);
+}
+
 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
 {
 	do {

block/blk-rq-qos.h

@@ -35,6 +35,7 @@ struct rq_qos {
 struct rq_qos_ops {
 	void (*throttle)(struct rq_qos *, struct bio *);
 	void (*track)(struct rq_qos *, struct request *, struct bio *);
+	void (*merge)(struct rq_qos *, struct request *, struct bio *);
 	void (*issue)(struct rq_qos *, struct request *);
 	void (*requeue)(struct rq_qos *, struct request *);
 	void (*done)(struct rq_qos *, struct request *);
@@ -135,6 +136,7 @@ void __rq_qos_issue(struct rq_qos *rqos, struct request *rq);
 void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq);
 void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio);
 void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio);
+void __rq_qos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio);
 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio);
 
 static inline void rq_qos_cleanup(struct request_queue *q, struct bio *bio)
@@ -185,6 +187,13 @@ static inline void rq_qos_track(struct request_queue *q, struct request *rq,
 		__rq_qos_track(q->rq_qos, rq, bio);
 }
 
+static inline void rq_qos_merge(struct request_queue *q, struct request *rq,
+				struct bio *bio)
+{
+	if (q->rq_qos)
+		__rq_qos_merge(q->rq_qos, rq, bio);
+}
+
 void rq_qos_exit(struct request_queue *);
 
 #endif