function writeConfigFile($file = null, $layer = 'user', $data = null)
    {
        $this->_lazyChannelSetup($layer);
        if ($layer == 'both' || $layer == 'all') {
            foreach ($this->files as $type => $file) {
                $err = $this->writeConfigFile($file, $type, $data);
                if (PEAR::isError($err)) {
                    return $err;
                }
            }
            return true;
        }

        if (empty($this->files[$layer])) {
            return $this->raiseError("unknown config file type `$layer'");
        }

        if ($file === null) {
            $file = $this->files[$layer];
        }

        $data = ($data === null) ? $this->configuration[$layer] : $data;
        $this->_encodeOutput($data);
        $opt = array('-p', dirname($file));
        if (!@System::mkDir($opt)) {
            return $this->raiseError("could not create directory: " . dirname($file));
        }

        if (file_exists($file) && is_file($file) && !is_writeable($file)) {
            return $this->raiseError("no write access to $file!");
        }

        $fp = @fopen($file, "w");
        if (!$fp) {
            return $this->raiseError("PEAR_Config::writeConfigFile fopen('$file','w') failed ($php_errormsg)");
        }

        $contents = "#PEAR_Config 0.9\n" . serialize($data);
        if (!@fwrite($fp, $contents)) {
            return $this->raiseError("PEAR_Config::writeConfigFile: fwrite failed ($php_errormsg)");
        }
        return true;
    }