public function update($fileList)
    {
        $csums = array();

        foreach ($fileList as $file) {
            if (file_exists($file)) {
                $hash = $this->calculateHash($file);
                $csums[$this->_makeRelative($file)] = $hash;
            }
        }

        $this->data = $csums;

        $this->write();

        return $csums;
    }