block: Kill bio_segments()/bi_vcnt usage

When we start sharing biovecs, keeping bi_vcnt accurate for splits is
going to be error prone - and unnecessary, if we refactor some code.

So bio_segments() has to go - but most of the existing users just needed
to know if the bio had multiple segments, which is easier - add a
bio_multiple_segments() for them.

(Two of the current uses of bio_segments() are going to go away in a
couple patches, but the current implementation of bio_segments() is
unsafe as soon as we start doing driver conversions for immutable
biovecs - so implement a dumb version for bisectability, it'll go away
in a couple patches)

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Neil Brown <neilb@suse.de>
Cc: Nagalakshmi Nandigama <Nagalakshmi.Nandigama@lsi.com>
Cc: Sreekanth Reddy <Sreekanth.Reddy@lsi.com>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>

3 files changed, 25 insertions, 32 deletions

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index 9b5b6a41a9b6..6e04f3bb0286 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -24,7 +24,8 @@ static void bch_generic_make_request_hack(struct bio *bio)
 	if (bio->bi_iter.bi_idx) {
 		struct bio_vec bv;
 		struct bvec_iter iter;
-		struct bio *clone = bio_alloc(GFP_NOIO, bio_segments(bio));
+		unsigned segs = bio_segments(bio);
+		struct bio *clone = bio_alloc(GFP_NOIO, segs);
 
 		bio_for_each_segment(bv, bio, iter)
 			clone->bi_io_vec[clone->bi_vcnt++] = bv;
@@ -32,7 +33,7 @@ static void bch_generic_make_request_hack(struct bio *bio)
 		clone->bi_iter.bi_sector = bio->bi_iter.bi_sector;
 		clone->bi_bdev		= bio->bi_bdev;
 		clone->bi_rw		= bio->bi_rw;
-		clone->bi_vcnt		= bio_segments(bio);
+		clone->bi_vcnt		= segs;
 		clone->bi_iter.bi_size	= bio->bi_iter.bi_size;
 
 		clone->bi_private	= bio;
@@ -133,40 +134,32 @@ out:
 
 static unsigned bch_bio_max_sectors(struct bio *bio)
 {
-	unsigned ret = bio_sectors(bio);
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-	unsigned max_segments = min_t(unsigned, BIO_MAX_PAGES,
-				      queue_max_segments(q));
+	struct bio_vec bv;
+	struct bvec_iter iter;
+	unsigned ret = 0, seg = 0;
 
 	if (bio->bi_rw & REQ_DISCARD)
-		return min(ret, q->limits.max_discard_sectors);
-
-	if (bio_segments(bio) > max_segments ||
-	    q->merge_bvec_fn) {
-		struct bio_vec bv;
-		struct bvec_iter iter;
-		unsigned seg = 0;
-
-		ret = 0;
+		return min(bio_sectors(bio), q->limits.max_discard_sectors);
 
-		bio_for_each_segment(bv, bio, iter) {
-			struct bvec_merge_data bvm = {
-				.bi_bdev	= bio->bi_bdev,
-				.bi_sector	= bio->bi_iter.bi_sector,
-				.bi_size	= ret << 9,
-				.bi_rw		= bio->bi_rw,
-			};
-
-			if (seg == max_segments)
-				break;
+	bio_for_each_segment(bv, bio, iter) {
+		struct bvec_merge_data bvm = {
+			.bi_bdev	= bio->bi_bdev,
+			.bi_sector	= bio->bi_iter.bi_sector,
+			.bi_size	= ret << 9,
+			.bi_rw		= bio->bi_rw,
+		};
+
+		if (seg == min_t(unsigned, BIO_MAX_PAGES,
+				 queue_max_segments(q)))
+			break;
 
-			if (q->merge_bvec_fn &&
-			    q->merge_bvec_fn(q, &bvm, &bv) < (int) bv.bv_len)
-				break;
+		if (q->merge_bvec_fn &&
+		    q->merge_bvec_fn(q, &bvm, &bv) < (int) bv.bv_len)
+			break;
 
-			seg++;
-			ret += bv.bv_len >> 9;
-		}
+		seg++;
+		ret += bv.bv_len >> 9;
 	}
 
 	ret = min(ret, queue_max_sectors(q));
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index e38d1d3226f3..8ee1a6c658b4 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -528,7 +528,7 @@ static void raid0_make_request(struct mddev *mddev, struct bio *bio)
 		sector_t sector = bio->bi_iter.bi_sector;
 		struct bio_pair *bp;
 		/* Sanity check -- queue functions should prevent this happening */
-		if (bio_segments(bio) > 1)
+		if (bio_multiple_segments(bio))
 			goto bad_map;
 		/* This is a one page bio that upper layers
 		 * refuse to split for us, so we need to split it.
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index dbf3b63c2754..ac4bfa438c57 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1188,7 +1188,7 @@ static void make_request(struct mddev *mddev, struct bio * bio)
 			 || conf->prev.near_copies < conf->prev.raid_disks))) {
 		struct bio_pair *bp;
 		/* Sanity check -- queue functions should prevent this happening */
-		if (bio_segments(bio) > 1)
+		if (bio_multiple_segments(bio))
 			goto bad_map;
 		/* This is a one page bio that upper layers
 		 * refuse to split for us, so we need to split it.