block: move the call to get_max_io_size out of blk_bio_segment_split

Prepare for reusing blk_bio_segment_split for (file system controlled)
splits of REQ_OP_ZONE_APPEND bios by letting the caller control the
maximum size of the bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20220727162300.3089193-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/blk-merge.c

@@ -250,11 +250,12 @@ static bool bvec_split_segs(const struct request_queue *q,
  * @q:    [in] request queue pointer
  * @segs: [out] number of segments in the bio with the first half of the sectors
  * @bs:	  [in] bio set to allocate the clone from
+ * @max_bytes: [in] maximum number of bytes per bio
  *
  * Clone @bio, update the bi_iter of the clone to represent the first sectors
  * of @bio and update @bio->bi_iter to represent the remaining sectors. The
  * following is guaranteed for the cloned bio:
- * - That it has at most get_max_io_size(@bio, @q) sectors.
+ * - That it has at most @max_bytes worth of data
  * - That it has at most queue_max_segments(@q) segments.
  *
  * Except for discard requests the cloned bio will point at the bi_io_vec of
@@ -264,12 +265,11 @@ static bool bvec_split_segs(const struct request_queue *q,
  * split bio has finished.
  */
 static struct bio *bio_split_rw(struct bio *bio, struct request_queue *q,
-		unsigned *segs, struct bio_set *bs)
+		unsigned *segs, struct bio_set *bs, unsigned max_bytes)
 {
 	struct bio_vec bv, bvprv, *bvprvp = NULL;
 	struct bvec_iter iter;
 	unsigned nsegs = 0, bytes = 0;
-	const unsigned max_bytes = get_max_io_size(bio, q) << 9;
 	const unsigned max_segs = queue_max_segments(q);
 
 	bio_for_each_bvec(bv, bio, iter) {
@@ -343,7 +343,8 @@ struct bio *__bio_split_to_limits(struct bio *bio, struct request_queue *q,
 		split = bio_split_write_zeroes(bio, q, nr_segs, bs);
 		break;
 	default:
-		split = bio_split_rw(bio, q, nr_segs, bs);
+		split = bio_split_rw(bio, q, nr_segs, bs,
+				get_max_io_size(bio, q) << SECTOR_SHIFT);
 		break;
 	}