void open(final int flags, final int access, final int attrs, final int options) throws SmbException {
        if (isOpen()) {
            return;
        }
        fid = open0(flags, access, attrs, options);
        opened = true;
        tree_num = tree.tree_num;
    }

    boolean isOpen() {
        return opened && isConnected() && tree_num == tree.tree_num;
    }