btrfs: split bios to the fs sector size boundary

Btrfs like other file systems can't really deal with I/O not aligned to
it's internal block size (which strangely is called sector size in
btrfs, for historical reasons), but the block layer split helper doesn't
even know about that.

Round down the split boundary so that all I/Os are aligned.

Fixes: d5e4377 ("btrfs: split zone append bios in btrfs_submit_bio")
CC: [email protected] # 6.12
Reviewed-by: Johannes Thumshirn <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: Christoph Hellwig

fs/btrfs/bio.c

@@ -649,8 +649,14 @@ static u64 btrfs_append_map_length(struct btrfs_bio *bbio, u64 map_length)
 	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;
+	if (sector_offset) {
+		/*
+		 * bio_split_rw_at() could split at a size smaller than our
+		 * sectorsize and thus cause unaligned I/Os.  Fix that by
+		 * always rounding down to the nearest boundary.
+		 */
+		return ALIGN_DOWN(sector_offset << SECTOR_SHIFT, bbio->fs_info->sectorsize);
+	}
 	return map_length;
 }