Btrfs: create special free space cache inode

In order to save free space cache, we need an inode to hold the data, and we
need a special item to point at the right inode for the right block group.  So
first, create a special item that will point to the right inode, and the number
of extent entries we will have and the number of bitmaps we will have.  We
truncate and pre-allocate space everytime to make sure it's uptodate.

This feature will be turned on as soon as you mount with -o space_cache, however
it is safe to boot into old kernels, they will just generate the cache the old
fashion way.  When you boot back into a newer kernel we will notice that we
modified and not the cache and automatically discard the cache.

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index 890a8e79011b..45be29e5f01e 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -27,6 +27,17 @@ struct btrfs_free_space {
         struct list_head list;
 };
 
+struct inode *lookup_free_space_inode(struct btrfs_root *root,
+                                      struct btrfs_block_group_cache
+                                      *block_group, struct btrfs_path *path);
+int create_free_space_inode(struct btrfs_root *root,
+                            struct btrfs_trans_handle *trans,
+                            struct btrfs_block_group_cache *block_group,
+                            struct btrfs_path *path);
+int btrfs_truncate_free_space_cache(struct btrfs_root *root,
+                                    struct btrfs_trans_handle *trans,
+                                    struct btrfs_path *path,
+                                    struct inode *inode);
 int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
                          u64 bytenr, u64 size);
 int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,