[PATCH RFC 02/11] btrfs: refactor btrfs_map_bio()

[Qu Wenruo <wqu@suse.com>]

Currently in btrfs_map_bio() we call __btrfs_map_block(), then using the
returned bioc to submit real stripes.

This is fine if we're only going to handle one bio a time.

For the incoming bio split at btrfs_map_bio() time, we want to handle
several differnet bios, thus there we introduce a new helper,
submit_one_mapped_range() to handle the submission part, making it much
easier to make it work in a loop.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/volumes.c | 65 ++++++++++++++++++++++++++++------------------
 1 file changed, 40 insertions(+), 25 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3dc1de376966..1d40f4fa64a3 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6772,29 +6772,15 @@ static void bioc_error(struct btrfs_io_context *bioc, struct bio *bio, u64 logic
 	}
 }
 
-blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
-			   int mirror_num)
+static int submit_one_mapped_range(struct btrfs_fs_info *fs_info, struct bio *bio,
+				   struct btrfs_io_context *bioc, u64 map_length,
+				   int mirror_num)
 {
-	struct btrfs_device *dev;
 	struct bio *first_bio = bio;
-	u64 logical = bio->bi_iter.bi_sector << 9;
-	u64 length = 0;
-	u64 map_length;
-	int ret;
-	int dev_nr;
+	u64 logical = bio->bi_iter.bi_sector << SECTOR_SHIFT;
 	int total_devs;
-	struct btrfs_io_context *bioc = NULL;
-
-	length = bio->bi_iter.bi_size;
-	map_length = length;
-
-	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);
-	}
+	int dev_nr;
+	int ret;
 
 	total_devs = bioc->num_stripes;
 	bioc->orig_bio = first_bio;
@@ -6813,18 +6799,19 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 						    mirror_num, 1);
 		}
 
-		btrfs_bio_counter_dec(fs_info);
-		return errno_to_blk_status(ret);
+		return ret;
 	}
 
-	if (map_length < length) {
+	if (map_length < bio->bi_iter.bi_size) {
 		btrfs_crit(fs_info,
-			   "mapping failed logical %llu bio len %llu len %llu",
-			   logical, length, map_length);
+			   "mapping failed logical %llu bio len %u len %llu",
+			   logical, bio->bi_iter.bi_size, map_length);
 		BUG();
 	}
 
 	for (dev_nr = 0; dev_nr < total_devs; dev_nr++) {
+		struct btrfs_device *dev;
+
 		dev = bioc->stripes[dev_nr].dev;
 		if (!dev || !dev->bdev || test_bit(BTRFS_DEV_STATE_MISSING,
 						   &dev->dev_state) ||
@@ -6841,6 +6828,34 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 
 		submit_stripe_bio(bioc, bio, bioc->stripes[dev_nr].physical, dev);
 	}
+	return 0;
+}
+
+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;
+	int ret;
+	struct btrfs_io_context *bioc = NULL;
+
+	length = bio->bi_iter.bi_size;
+	map_length = length;
+
+	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 = submit_one_mapped_range(fs_info, bio, bioc, map_length, mirror_num);
+	if (ret < 0) {
+		btrfs_bio_counter_dec(fs_info);
+		return errno_to_blk_status(ret);
+	}
 	btrfs_bio_counter_dec(fs_info);
 	return BLK_STS_OK;
 }
-- 
2.34.0