block: rework bio splitting

The current setup with bio_may_exceed_limit and __bio_split_to_limits
is a bit of a mess.

Change it so that __bio_split_to_limits does all the work and is just
a variant of bio_split_to_limits that returns nr_segs.  This is done
by inlining it and instead have the various bio_split_* helpers directly
submit the potentially split bios.

To support btrfs, the rw version has a lower level helper split out
that just returns the offset to split.  This turns out to nicely clean
up the btrfs flow as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Sterba <dsterba@suse.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Link: https://lore.kernel.org/r/20240826173820.1690925-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 18 insertions, 12 deletions

diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
index f04d93109960..5ae769184907 100644
--- a/fs/btrfs/bio.c
+++ b/fs/btrfs/bio.c
@@ -73,20 +73,13 @@ struct btrfs_bio *btrfs_bio_alloc(unsigned int nr_vecs, blk_opf_t opf,
 
 static struct btrfs_bio *btrfs_split_bio(struct btrfs_fs_info *fs_info,
 					 struct btrfs_bio *orig_bbio,
-					 u64 map_length, bool use_append)
+					 u64 map_length)
 {
 	struct btrfs_bio *bbio;
 	struct bio *bio;
 
-	if (use_append) {
-		unsigned int nr_segs;
-
-		bio = bio_split_rw(&orig_bbio->bio, &fs_info->limits, &nr_segs,
-				   &btrfs_clone_bioset, map_length);
-	} else {
-		bio = bio_split(&orig_bbio->bio, map_length >> SECTOR_SHIFT,
-				GFP_NOFS, &btrfs_clone_bioset);
-	}
+	bio = bio_split(&orig_bbio->bio, map_length >> SECTOR_SHIFT, GFP_NOFS,
+			&btrfs_clone_bioset);
 	bbio = btrfs_bio(bio);
 	btrfs_bio_init(bbio, fs_info, NULL, orig_bbio);
 	bbio->inode = orig_bbio->inode;
@@ -664,6 +657,19 @@ static bool btrfs_wq_submit_bio(struct btrfs_bio *bbio,
 	return true;
 }
 
+static u64 btrfs_append_map_length(struct btrfs_bio *bbio, u64 map_length)
+{
+	unsigned int nr_segs;
+	int sector_offset;
+
+	map_length = min(map_length, bbio->fs_info->max_zone_append_size);
+	sector_offset = bio_split_rw_at(&bbio->bio, &bbio->fs_info->limits,
+					&nr_segs, map_length);
+	if (sector_offset)
+		return sector_offset << SECTOR_SHIFT;
+	return map_length;
+}
+
 static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
 {
 	struct btrfs_inode *inode = bbio->inode;
@@ -691,10 +697,10 @@ static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
 
 	map_length = min(map_length, length);
 	if (use_append)
-		map_length = min(map_length, fs_info->max_zone_append_size);
+		map_length = btrfs_append_map_length(bbio, map_length);
 
 	if (map_length < length) {
-		bbio = btrfs_split_bio(fs_info, bbio, map_length, use_append);
+		bbio = btrfs_split_bio(fs_info, bbio, map_length);
 		bio = &bbio->bio;
 	}