[dm-devel] [PATCH 13/17] btrfs: allow btrfs_map_bio() to split bio according to chunk stripe boundaries

[Qu Wenruo]

With the new btrfs_bio_split() helper, we are able to split bio
according to chunk stripe boundaries at btrfs_map_bio() time.

Although currently due bio split at buffered/compressed/direct IO time,
this ability is not yet utilized.

Signed-off-by: Qu Wenruo <wqu at suse.com>
---
 fs/btrfs/volumes.c | 48 ++++++++++++++++++++++++++++++----------------
 1 file changed, 31 insertions(+), 17 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 365e43bbfd14..35ba1ea95295 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6893,29 +6893,43 @@ static int submit_one_mapped_range(struct btrfs_fs_info *fs_info, struct bio *bi
 blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 			   int mirror_num)
 {
-	u64 logical = bio->bi_iter.bi_sector << 9;
-	u64 length = 0;
-	u64 map_length;
+	const u64 orig_logical = bio->bi_iter.bi_sector << SECTOR_SHIFT;
+	const unsigned int orig_length = bio->bi_iter.bi_size;
+	const enum btrfs_map_op op = btrfs_op(bio);
+	u64 cur_logical = orig_logical;
 	int ret;
-	struct btrfs_io_context *bioc = NULL;
 
-	length = bio->bi_iter.bi_size;
-	map_length = length;
+	while (cur_logical < orig_logical + orig_length) {
+		u64 map_length = orig_logical + orig_length - cur_logical;
+		struct btrfs_io_context *bioc = NULL;
+		struct bio *cur_bio;
 
-	btrfs_bio_counter_inc_blocked(fs_info);
-	ret = __btrfs_map_block(fs_info, btrfs_op(bio), logical,
-				&map_length, &bioc, mirror_num, 1);
-	if (ret) {
-		btrfs_bio_counter_dec(fs_info);
-		return errno_to_blk_status(ret);
-	}
+		ret = __btrfs_map_block(fs_info, op, cur_logical, &map_length,
+					&bioc, mirror_num, 1);
+		if (ret)
+			return errno_to_blk_status(ret);
 
-	ret = submit_one_mapped_range(fs_info, bio, bioc, map_length, mirror_num);
-	if (ret < 0) {
+		if (cur_logical + map_length < orig_logical + orig_length) {
+			/*
+			 * For now zoned write should never cross stripe
+			 * boundary
+			 */
+			ASSERT(bio_op(bio) != REQ_OP_ZONE_APPEND);
+
+			/* Split the bio */
+			cur_bio = btrfs_bio_split(fs_info, bio, map_length);
+		} else {
+			/* Use the existing bio directly */
+			cur_bio = bio;
+		}
+		btrfs_bio_counter_inc_blocked(fs_info);
+		ret = submit_one_mapped_range(fs_info, cur_bio, bioc,
+					      map_length, mirror_num);
 		btrfs_bio_counter_dec(fs_info);
-		return errno_to_blk_status(ret);
+		if (ret < 0)
+			return errno_to_blk_status(ret);
+		cur_logical += map_length;
 	}
-	btrfs_bio_counter_dec(fs_info);
 	return BLK_STS_OK;
 }
 
-- 
2.34.1