ocfs2: temporarily remove extent map caching

The code in extent_map.c is not prepared to deal with a subtree being
rotated between lookups. This can happen when filling holes in sparse files.
Instead of a lengthy patch to update the code (which would likely lose the
benefit of caching subtree roots), we remove most of the algorithms and
implement a simple path based lookup. A less ambitious extent caching scheme
will be added in a later patch.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/alloc.h

@@ -80,4 +80,7 @@ int ocfs2_commit_truncate(struct ocfs2_super *osb,
 			  struct buffer_head *fe_bh,
 			  struct ocfs2_truncate_context *tc);
 
+int ocfs2_find_leaf(struct inode *inode, struct ocfs2_extent_list *root_el,
+		    u32 cpos, struct buffer_head **leaf_bh);
+
 #endif /* OCFS2_ALLOC_H */