Btrfs: superblock duplication

This patch implements superblock duplication. Superblocks
are stored at offset 16K, 64M and 256G on every devices.
Spaces used by superblocks are preserved by the allocator,
which uses a reverse mapping function to find the logical
addresses that correspond to superblocks. Thank you,

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 717e94811e4e..c0ff404c31b7 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -19,8 +19,20 @@
 #ifndef __DISKIO__
 #define __DISKIO__
 
-#define BTRFS_SUPER_INFO_OFFSET (16 * 1024)
+#define BTRFS_SUPER_INFO_OFFSET (64 * 1024)
 #define BTRFS_SUPER_INFO_SIZE 4096
+
+#define BTRFS_SUPER_MIRROR_MAX   3
+#define BTRFS_SUPER_MIRROR_SHIFT 12
+
+static inline u64 btrfs_sb_offset(int mirror)
+{
+        u64 start = 16 * 1024;
+        if (mirror)
+                return start << (BTRFS_SUPER_MIRROR_SHIFT * mirror);
+        return BTRFS_SUPER_INFO_OFFSET;
+}
+
 struct btrfs_device;
 struct btrfs_fs_devices;
 
@@ -37,7 +49,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                               char *options);
 int close_ctree(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
-                      struct btrfs_root *root);
+                      struct btrfs_root *root, int max_mirrors);
+struct buffer_head *btrfs_read_dev_super(struct block_device *bdev);
 int btrfs_commit_super(struct btrfs_root *root);
 struct extent_buffer *btrfs_find_tree_block(struct btrfs_root *root,
                                             u64 bytenr, u32 blocksize);