public function getConfigurationSources(ConfigInterface $conf)
    {
        if ($conf->hasOption('config-file')) {
            $file = $conf->getOption('config-file');
            if (isset($file)) {
                if (!strstr($file, '/')) {
                    $file = $conf->getOption('config-dir').$file;
                }

                return array($file);
            }
        }
        // load every xml file in config dir
        $dir = $conf->getOption('config-dir');
        $list = glob("{$dir}*.xml", GLOB_ERR);
        if ($list === false) {
            throw new IOException($dir, null,
                 "config-dir '$dir' is not readable",
                 IOException::FAILURE_NOT_READABLE);
        }

        return $list;
    }