ovl: generalize the lower_layers[] array

Rename lower_layers[] array to layers[], extend its size by one and
initialize layers[0] with upper layer values.  Lower layers are now
addressed with index 1..numlower.  layers[0] is reserved even with lower
only overlay.

[SzM: replace ofs->numlower with ofs->numlayer, the latter's value is
incremented by one]

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 28348c4..64baf04 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -45,10 +45,10 @@ struct ovl_path {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
 	struct vfsmount *upper_mnt;
-	unsigned int numlower;
+	unsigned int numlayer;
 	/* Number of unique lower sb that differ from upper sb */
 	unsigned int numlowerfs;
-	struct ovl_layer *lower_layers;
+	struct ovl_layer *layers;
 	struct ovl_sb *lower_fs;
 	/* workbasedir is the path at workdir= mount option */
 	struct dentry *workbasedir;