ubifs: Implement UBIFS_FLG_DOUBLE_HASH

This feature flag indicates that all directory entry nodes have a 32bit
cookie set and therefore UBIFS is allowed to perform lookups by hash.

Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/fs/ubifs/ubifs-media.h b/fs/ubifs/ubifs-media.h
index 249124d..0cbdc6b 100644
--- a/fs/ubifs/ubifs-media.h
+++ b/fs/ubifs/ubifs-media.h
@@ -418,10 +418,13 @@
  *
  * UBIFS_FLG_BIGLPT: if "big" LPT model is used if set
  * UBIFS_FLG_SPACE_FIXUP: first-mount "fixup" of free space within LEBs needed
+ * UBIFS_FLG_DOUBLE_HASH: store a 32bit cookie in directory entry nodes to
+ *			  support 64bit cookies for lookups by hash
  */
 enum {
 	UBIFS_FLG_BIGLPT = 0x02,
 	UBIFS_FLG_SPACE_FIXUP = 0x04,
+	UBIFS_FLG_DOUBLE_HASH = 0x08,
 };
 
 /**