def getFeatureReport(self, report_num=0, length=63):
        """
        Receive a feature report.
        Blocks, unless you configured provided file (descriptor) to be
        non-blocking.
        """
        length += 1
        buf = bytearray(length)
        buf[0] = report_num
        self._ioctl(
            _HIDIOCGFEATURE(length),
            (ctypes.c_char * length).from_buffer(buf),
            True,
        )
        return buf