ovl: store layer index in ovl_layer

Store the fs root layer index inside ovl_layer struct, so we can
get the root fs layer index from merge dir lower layer instead of
find it with ovl_find_layer() helper.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/namei.c

@@ -572,18 +572,6 @@ int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 	return (idx < oe->numlower) ? idx + 1 : -1;
 }
 
-static int ovl_find_layer(struct ovl_fs *ofs, struct ovl_path *path)
-{
-	int i;
-
-	for (i = 0; i < ofs->numlower; i++) {
-		if (ofs->lower_layers[i].mnt == path->layer->mnt)
-			break;
-	}
-
-	return i;
-}
-
 /* Fix missing 'origin' xattr */
 static int ovl_fix_origin(struct dentry *dentry, struct dentry *lower,
 			  struct dentry *upper)
@@ -733,11 +721,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 		if (d.redirect && d.redirect[0] == '/' && poe != roe) {
 			poe = roe;
-
 			/* Find the current layer on the root dentry */
-			i = ovl_find_layer(ofs, &lower);
-			if (WARN_ON(i == ofs->numlower))
-				break;
+			i = lower.layer->idx - 1;
 		}
 	}
 

fs/overlayfs/ovl_entry.h

@@ -22,6 +22,8 @@ struct ovl_config {
 struct ovl_layer {
 	struct vfsmount *mnt;
 	dev_t pseudo_dev;
+	/* Index of this layer in fs root (upper == 0) */
+	int idx;
 };
 
 struct ovl_path {

fs/overlayfs/super.c

@@ -1106,6 +1106,7 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 
 		ofs->lower_layers[ofs->numlower].mnt = mnt;
 		ofs->lower_layers[ofs->numlower].pseudo_dev = dev;
+		ofs->lower_layers[ofs->numlower].idx = i + 1;
 		ofs->numlower++;
 
 		/* Check if all lower layers are on same sb */