def save_config(self, fname, output_dir, cp=None):
        """ Writes configuration file to disk and returns a pycbc.workflow.File
        instance for the configuration file.

        Parameters
        -----------
        fname : string
            The filename of the configuration file written to disk.
        output_dir : string
            The directory where the file is written to disk.
        cp : ConfigParser object
            The ConfigParser object to write. If None then uses self.cp.

        Returns
        -------
        FileList
            The FileList object with the configuration file.
        """
        cp = self.cp if cp is None else cp
        ini_file_path = os.path.join(output_dir, fname)
        with open(ini_file_path, "wb") as fp:
            cp.write(fp)
        ini_file = FileList([File(self.ifos, "",
                                  self.analysis_time,
                                  file_url="file://" + ini_file_path)])
        return ini_file