code: private void loadEnabledPermissionCheckingDirs(Configuration conf) 
        throws IOException {
      if (this.isPermissionEnabled) {
        String[] permissionCheckingDirs = 
            conf.getStrings("dfs.permissions.checking.paths", "/");
        int numDirs = permissionCheckingDirs.length;
        if (numDirs == 0) {
          return;
        }
        this.permissionEnabled = new INode[numDirs];
        int i = 0;
        for (String src : permissionCheckingDirs) {
          INode permissionEnabledNode = this.dir.getINode(src);
          if (permissionEnabledNode == null) {
            throw new IOException(
                "Non-existent path for disabling permission Checking: " + src);
          }
          permissionEnabled[i++] = permissionEnabledNode;
        }
      }
    }
docs: Load the predefined paths that should enable permission checking,
  each of which represents the root of a subtree
  whose nodes should check permission
  
  @param conf configuration
  @throws IOException if a predefine path does not exist