ovl: helper to iterate layers

Add helper to iterate through all the layers, starting from the upper layer
(if exists) and continuing down through the lower layers.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

2 files changed, 22 insertions, 0 deletions

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index d39eaa8f5e47..d176b679f526 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -135,6 +135,7 @@ void ovl_dentry_version_inc(struct dentry *dentry);
 void ovl_path_upper(struct dentry *dentry, struct path *path);
 void ovl_path_lower(struct dentry *dentry, struct path *path);
 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path);
+int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
 struct dentry *ovl_dentry_upper(struct dentry *dentry);
 struct dentry *ovl_dentry_lower(struct dentry *dentry);
 struct dentry *ovl_dentry_real(struct dentry *dentry);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 460d866b97a2..07e4c576e93e 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -305,6 +305,27 @@ static inline struct dentry *ovl_lookup_real(struct dentry *dir,
         return dentry;
 }
 
+/*
+ * Returns next layer in stack starting from top.
+ * Returns -1 if this is the last layer.
+ */
+int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        BUG_ON(idx < 0);
+        if (idx == 0) {
+                ovl_path_upper(dentry, path);
+                if (path->dentry)
+                        return oe->numlower ? 1 : -1;
+                idx++;
+        }
+        BUG_ON(idx > oe->numlower);
+        *path = oe->lowerstack[idx - 1];
+
+        return (idx < oe->numlower) ? idx + 1 : -1;
+}
+
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                           unsigned int flags)
 {