def _openTunnel(self, name, mode):
        """
        Open the named tunnel using the given mode.

        @param name: The name of the tunnel to open.
        @type name: L{bytes}

        @param mode: Flags from L{TunnelFlags} with exactly one of
            L{TunnelFlags.IFF_TUN} or L{TunnelFlags.IFF_TAP} set.

        @return: A L{_TunnelDescription} representing the newly opened tunnel.
        """
        flags = (
            self._system.O_RDWR | self._system.O_CLOEXEC |
            self._system.O_NONBLOCK)
        config = struct.pack("%dsH" % (_IFNAMSIZ,), name, mode.value)
        fileno = self._system.open(_TUN_KO_PATH, flags)
        result = self._system.ioctl(fileno, _TUNSETIFF, config)
        return _TunnelDescription(fileno, result[:_IFNAMSIZ].strip(b'\x00'))

        Open the named tunnel using the given mode.

        @param name: The name of the tunnel to open.
        @type name: L{bytes}

        @param mode: Flags from L{TunnelFlags} with exactly one of
            L{TunnelFlags.IFF_TUN} or L{TunnelFlags.IFF_TAP} set.

        @return: A L{_TunnelDescription} representing the newly opened tunnel.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/pair/tuntap.py