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/sb.c b/fs/ubifs/sb.c
index 3cbb904..4a2b4c3 100644
--- a/fs/ubifs/sb.c
+++ b/fs/ubifs/sb.c
@@ -163,6 +163,7 @@ static int create_default_filesystem(struct ubifs_info *c)
 	tmp64 = (long long)max_buds * c->leb_size;
 	if (big_lpt)
 		sup_flags |= UBIFS_FLG_BIGLPT;
+	sup_flags |= UBIFS_FLG_DOUBLE_HASH;
 
 	sup->ch.node_type  = UBIFS_SB_NODE;
 	sup->key_hash      = UBIFS_KEY_HASH_R5;
@@ -620,6 +621,7 @@ int ubifs_read_superblock(struct ubifs_info *c)
 	memcpy(&c->uuid, &sup->uuid, 16);
 	c->big_lpt = !!(sup_flags & UBIFS_FLG_BIGLPT);
 	c->space_fixup = !!(sup_flags & UBIFS_FLG_SPACE_FIXUP);
+	c->double_hash = !!(sup_flags & UBIFS_FLG_DOUBLE_HASH);
 
 	/* Automatically increase file system size to the maximum size */
 	c->old_leb_cnt = c->leb_cnt;