def _setup_reserved_dhcp_port(self, network, device_id, dhcp_subnets):
        LOG.debug('DHCP port %(device_id)s on network %(network_id)s'
                  ' does not yet exist. Checking for a reserved port.',
                  {'device_id': device_id, 'network_id': network.id})
        for port in network.ports:
            port_device_id = getattr(port, 'device_id', None)
            if port_device_id == n_const.DEVICE_ID_RESERVED_DHCP_PORT:
                try:
                    port = self.plugin.update_dhcp_port(
                        port.id, {'port': {'network_id': network.id,
                                           'device_id': device_id}})
                except oslo_messaging.RemoteError as e:
                    if e.exc_type == n_exc.DhcpPortInUse:
                        LOG.info(_LI("Skipping DHCP port %s as it is "
                                     "already in use"), port.id)
                        continue
                    raise
                if port:
                    return port
Setup the reserved DHCP port, if there is one.
dataset/ETHPy150Open openstack/neutron/neutron/agent/linux/dhcp.py/DeviceManager._setup_reserved_dhcp_port