ovl: add ovl_allow_offline_changes() helper

Allows to check whether any of extended features are enabled
Signed-off-by: Vyacheslav Yurkov <Vyacheslav.Yurkov@bruker.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/overlayfs.h

@@ -263,6 +263,18 @@ static inline bool ovl_open_flags_need_copy_up(int flags)
 	return ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC));
 }
 
+static inline bool ovl_allow_offline_changes(struct ovl_fs *ofs)
+{
+	/*
+	 * To avoid regressions in existing setups with overlay lower offline
+	 * changes, we allow lower changes only if none of the new features
+	 * are used.
+	 */
+	return (!ofs->config.index && !ofs->config.metacopy &&
+		!ofs->config.redirect_dir && ofs->config.xino != OVL_XINO_ON);
+}
+
+
 /* util.c */
 int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);

fs/overlayfs/super.c

@@ -1599,9 +1599,7 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
 	 * user opted-in to one of the new features that require following the
 	 * lower inode of non-dir upper.
 	 */
-	if (!ofs->config.index && !ofs->config.metacopy &&
-	    !ofs->config.redirect_dir && ofs->config.xino != OVL_XINO_ON &&
-	    uuid_is_null(uuid))
+	if (ovl_allow_offline_changes(ofs) && uuid_is_null(uuid))
 		return false;
 
 	for (i = 0; i < ofs->numfs; i++) {