Btrfs, scrub: repair the common data on RAID5/6 if it is corrupted

This patch implement the RAID5/6 common data repair function, the
implementation is similar to the scrub on the other RAID such as
RAID1, the differentia is that we don't read the data from the
mirror, we use the data repair function of RAID5/6.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 08980fa..01094bb 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -393,6 +393,10 @@
 int btrfs_map_block(struct btrfs_fs_info *fs_info, int rw,
 		    u64 logical, u64 *length,
 		    struct btrfs_bio **bbio_ret, int mirror_num);
+int btrfs_map_sblock(struct btrfs_fs_info *fs_info, int rw,
+		     u64 logical, u64 *length,
+		     struct btrfs_bio **bbio_ret, int mirror_num,
+		     u64 **raid_map_ret);
 int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 		     u64 chunk_start, u64 physical, u64 devid,
 		     u64 **logical, int *naddrs, int *stripe_len);