Btrfs: dummy extent buffers for tree mod log

The tree modification log needs two ways to create dummy extent buffers,
once by allocating a fresh one (to rebuild an old root) and once by
cloning an existing one (to make private rewind modifications) to it.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index b516c3b8dec6..96434a61d7c2 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -39,6 +39,7 @@
 #define EXTENT_BUFFER_STALE 6
 #define EXTENT_BUFFER_WRITEBACK 7
 #define EXTENT_BUFFER_IOERR 8
+#define EXTENT_BUFFER_DUMMY 9
 
 /* these are flags for extent_clear_unlock_delalloc */
 #define EXTENT_CLEAR_UNLOCK_PAGE 0x1
@@ -265,6 +266,8 @@ void set_page_extent_mapped(struct page *page);
 
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                                           u64 start, unsigned long len);
+struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len);
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
 struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
                                          u64 start, unsigned long len);
 void free_extent_buffer(struct extent_buffer *eb);