block: export bio_split_rw

bio_split_rw can be used by file systems to split and incoming write
bio into multiple bios fitting the hardware limit for use as ZONE_APPEND
bios.  Export it for initial use in btrfs.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

block/blk-merge.c

@@ -276,7 +276,7 @@ static bool bvec_split_segs(const struct queue_limits *lim,
  * responsible for ensuring that @bs is only destroyed after processing of the
  * split bio has finished.
  */
-static struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
+struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
 		unsigned *segs, struct bio_set *bs, unsigned max_bytes)
 {
 	struct bio_vec bv, bvprv, *bvprvp = NULL;
@@ -336,6 +336,7 @@ static struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
 	bio_clear_polled(bio);
 	return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
 }
+EXPORT_SYMBOL_GPL(bio_split_rw);
 
 /**
  * __bio_split_to_limits - split a bio to fit the queue limits

include/linux/bio.h

@@ -12,6 +12,8 @@
 
 #define BIO_MAX_VECS		256U
 
+struct queue_limits;
+
 static inline unsigned int bio_max_segs(unsigned int nr_segs)
 {
 	return min(nr_segs, BIO_MAX_VECS);
@@ -375,6 +377,8 @@ static inline void bip_set_seed(struct bio_integrity_payload *bip,
 void bio_trim(struct bio *bio, sector_t offset, sector_t size);
 extern struct bio *bio_split(struct bio *bio, int sectors,
 			     gfp_t gfp, struct bio_set *bs);
+struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
+		unsigned *segs, struct bio_set *bs, unsigned max_bytes);
 
 /**
  * bio_next_split - get next @sectors from a bio, splitting if necessary