block: simplify blk_recalc_rq_segments

Return the segement and let the callers assign them, which makes the code
a littler more obvious.  Also pass the request instead of q plus bio
chain, allowing for the use of rq_for_each_bvec.
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1152,7 +1152,7 @@ static int blk_cloned_rq_check_limits(struct request_queue *q,
 	 * Recalculate it to check the request correctly on this queue's
 	 * limitation.
 	 */
-	blk_recalc_rq_segments(rq);
+	rq->nr_phys_segments = blk_recalc_rq_segments(rq);
 	if (rq->nr_phys_segments > queue_max_segments(q)) {
 		printk(KERN_ERR "%s: over max segments limit. (%hu > %hu)\n",
 			__func__, rq->nr_phys_segments, queue_max_segments(q));
@@ -1421,7 +1421,7 @@ bool blk_update_request(struct request *req, blk_status_t error,
 		}
 
 		/* recalculate the number of segments */
-		blk_recalc_rq_segments(req);
+		req->nr_phys_segments = blk_recalc_rq_segments(req);
 	}
 
 	return true;

block/blk-merge.c

@@ -310,17 +310,16 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
 }
 EXPORT_SYMBOL(blk_queue_split);
 
-static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
-					     struct bio *bio)
+unsigned int blk_recalc_rq_segments(struct request *rq)
 {
 	unsigned int nr_phys_segs = 0;
-	struct bvec_iter iter;
+	struct req_iterator iter;
 	struct bio_vec bv;
 
-	if (!bio)
+	if (!rq->bio)
 		return 0;
 
-	switch (bio_op(bio)) {
+	switch (bio_op(rq->bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_SECURE_ERASE:
 	case REQ_OP_WRITE_ZEROES:
@@ -329,19 +328,11 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 		return 1;
 	}
 
-	for_each_bio(bio) {
-		bio_for_each_bvec(bv, bio, iter)
-			bvec_split_segs(q, &bv, &nr_phys_segs, NULL, UINT_MAX);
-	}
-
+	rq_for_each_bvec(bv, rq, iter)
+		bvec_split_segs(rq->q, &bv, &nr_phys_segs, NULL, UINT_MAX);
 	return nr_phys_segs;
 }
 
-void blk_recalc_rq_segments(struct request *rq)
-{
-	rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
-}
-
 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
 		struct scatterlist *sglist)
 {

block/blk.h

@@ -211,7 +211,7 @@ struct request *attempt_back_merge(struct request_queue *q, struct request *rq);
 struct request *attempt_front_merge(struct request_queue *q, struct request *rq);
 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 				struct request *next);
-void blk_recalc_rq_segments(struct request *rq);
+unsigned int blk_recalc_rq_segments(struct request *rq);
 void blk_rq_set_mixed_merge(struct request *rq);
 bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio);