code: INodeDirectory addToParent(byte[] localname,
                               INode newNode,
                               INodeDirectory parent,
                               boolean inheritPermission,
                               boolean propagateModTime,
                               int childIndex
                              ) throws FileNotFoundException {
      // insert into the parent children list
      newNode.name = localname;
      if(parent.addChild(newNode, inheritPermission, propagateModTime, childIndex) == null)
        return null;
      return parent;
    }
docs: Add new inode to the parent if specified.
  Optimized version of addNode() if parent is not null.
  
  @return  parent INode if new inode is inserted
  or null if it already exists.
  @throws  FileNotFoundException if parent does not exist or
  is not a directory.