def add_decrypt_chunk(
            self, final_path, internal_fdstart, offsets, symkey, iv,
            hmac_datafile):
        # type: (CryptoOffload, str, int, blobxfer.models.download.Offsets,
        #        bytes, bytes, str) -> None
        """Add a chunk to decrypt
        :param CryptoOffload self: this
        :param str final_path: final path
        :param int internal_fdstart: internal fd offset start
        :param blobxfer.models.download.Offsets offsets: offsets
        :param bytes symkey: symmetric key
        :param bytes iv: initialization vector
        :param str hmac_datafile: encrypted data file
        """
        self._task_queue.put(
            (CryptoAction.Decrypt, final_path, internal_fdstart, offsets,
             symkey, iv, hmac_datafile)
        )
Add a chunk to decrypt
        :param CryptoOffload self: this
        :param str final_path: final path
        :param int internal_fdstart: internal fd offset start
        :param blobxfer.models.download.Offsets offsets: offsets
        :param bytes symkey: symmetric key
        :param bytes iv: initialization vector
        :param str hmac_datafile: encrypted data file