Ensure gateway is set for prefix delegated subnets

With [1] gateway is no longer set for subnet created
with prefix delegation, but when adding the subnet
to the router it fails as it expects gateway to be
set.

This patch ensures gateway is set temporary to the first IP
of the subnet as it used to be just like the temporary CIDR.
Also need to ensure dhcp configuration is skipped to avoid the
original issue[2].

[1] https://review.opendev.org/c/openstack/neutron/+/699465
[2] https://bugs.launchpad.net/neutron/+bug/1856675

Closes-Bug: #1962306
Related-Bug: #1856675
Change-Id: I512f7d98ac99bb0ef06fd2acba09482e3436d18d
(cherry picked from commit 820b2e2665)

neutron/agent/linux/dhcp.py

@@ -1429,7 +1429,8 @@ class DeviceManager(object):
             skip_subnet = (
                 subnet.ip_version != ip_version or
                 not subnet.enable_dhcp or
-                subnet.gateway_ip is None)
+                subnet.gateway_ip is None or
+                subnet.subnetpool_id == constants.IPV6_PD_POOL_ID)
 
             if skip_subnet:
                 continue

neutron/db/db_base_plugin_common.py

@@ -160,7 +160,7 @@ class DbBasePluginCommon(object):
                'standard_attr_id': standard_attr_id,
                }
         res['gateway_ip'] = str(
-                subnet['gateway_ip']) if subnet['gateway_ip'] else None
+            subnet['gateway_ip']) if subnet['gateway_ip'] is not None else None
         # TODO(korzen) this method can get subnet as DB object or Subnet OVO,
         # so temporary workaround will be to fill in the fields in separate
         # ways. After converting all code pieces to use Subnet OVO, the latter

neutron/db/ipam_backend_mixin.py

@@ -58,9 +58,6 @@ class IpamBackendMixin(db_base_plugin_common.DbBasePluginCommon):
         if subnet.get('gateway_ip') is const.ATTR_NOT_SPECIFIED:
             if subnet.get('ip_version') == const.IP_VERSION_6:
                 gateway_ip = netaddr.IPNetwork(cidr_net).network
-                pd_net = netaddr.IPNetwork(const.PROVISIONAL_IPV6_PD_PREFIX)
-                if gateway_ip == pd_net.network:
-                    return
             else:
                 gateway_ip = netaddr.IPNetwork(cidr_net).network + 1
             return str(gateway_ip)

neutron/tests/fullstack/test_subnet.py

@@ -87,7 +87,12 @@ class TestSubnet(base.BaseFullStackTestCase):
                                      ipv6_ra_mode='slaac',
                                      subnetpool_id='prefix_delegation')
         subnet = self._show_subnet(subnet['id'])
-        self.assertIsNone(subnet['subnet']['gateway_ip'])
+        cidr = subnet['subnet']['cidr']
+        self.assertEqual(subnet['subnet']['gateway_ip'],
+                         str(netaddr.IPNetwork(cidr).network))
+        router = self.safe_client.create_router(self._project_id)
+        self.safe_client.add_router_interface(
+            router['id'], subnet['subnet']['id'])
 
     def test_create_subnet_ipv4_with_subnetpool(self):
         subnetpool_cidr = self.useFixture(

neutron/tests/functional/agent/linux/test_dhcp.py

@@ -16,6 +16,7 @@ from unittest import mock
 
 from neutron_lib import constants
 from oslo_config import cfg
+from oslo_utils import uuidutils
 
 from neutron.agent.linux import dhcp
 from neutron.agent.linux import ip_lib
@@ -47,6 +48,7 @@ class TestDhcp(functional_base.BaseSudoTestCase):
     def test_cleanup_stale_devices(self):
         plugin = mock.MagicMock()
         dev_mgr = dhcp.DeviceManager(self.conf, plugin)
+        spool_id = uuidutils.generate_uuid()
         network = {
             'id': 'foo_id',
             'tenant_id': 'foo_tenant',
@@ -57,6 +59,7 @@ class TestDhcp(functional_base.BaseSudoTestCase):
                                                   'ipv6_address_mode': None,
                                                   'ipv6_ra_mode': None,
                                                   'cidr': '10.0.0.0/24',
+                                                  'subnetpool_id': spool_id,
                                                   'ip_version':
                                                       constants.IP_VERSION_4,
                                                   'gateway_ip': '10.0.0.1'})]}

neutron/tests/functional/agent/test_dhcp_agent.py

@@ -108,6 +108,7 @@ class DHCPAgentOVSTestFramework(base.BaseSudoTestCase):
                            ip_version=lib_const.IP_VERSION_4,
                            prefix_override=None):
         cidr = self._IP_ADDRS[ip_version]['cidr']
+        spool_id = uuidutils.generate_uuid()
         if prefix_override is not None:
             cidr = '/'.join((cidr.split('/')[0], str(prefix_override)))
         sn_dict = dhcp.DictModel(
@@ -115,6 +116,7 @@ class DHCPAgentOVSTestFramework(base.BaseSudoTestCase):
             network_id=net_id,
             ip_version=ip_version,
             cidr=cidr,
+            subnetpool_id=spool_id,
             gateway_ip=self._IP_ADDRS[ip_version]['gateway'],
             enable_dhcp=dhcp_enabled,
             dns_nameservers=[],

neutron/tests/unit/agent/dhcp/test_agent.py

@@ -53,6 +53,8 @@ FAKE_NETWORK_UUID = '12345678-1234-5678-1234567890ab'
 FAKE_NETWORK_DHCP_NS = "qdhcp-%s" % FAKE_NETWORK_UUID
 FAKE_TENANT_ID = 'aaaaaaaa-aaaa-aaaa-aaaaaaaaaaaa'
 FAKE_PRIORITY = 6
+FAKE_V4_SUBNETPOOL_ID = 'kkkkkkkk-kkkk-kkkk-kkkk-kkkkkkkkkkkk'
+FAKE_V6_SUBNETPOOL_ID = 'jjjjjjjj-jjjj-jjjj-jjjj-jjjjjjjjjjjj'
 
 
 fake_subnet1_allocation_pools = dhcp.DictModel(id='', start='172.9.9.2',
@@ -64,6 +66,7 @@ fake_subnet1 = dhcp.DictModel(id='bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbb',
                               gateway_ip='172.9.9.1', host_routes=[],
                               dns_nameservers=[],
                               ip_version=const.IP_VERSION_4,
+                              subnetpool_id=FAKE_V4_SUBNETPOOL_ID,
                               ipv6_ra_mode=None, ipv6_address_mode=None,
                               allocation_pools=fake_subnet1_allocation_pools)
 
@@ -1744,6 +1747,7 @@ class FakeV4Subnet(object):
         self.cidr = '192.168.0.0/24'
         self.gateway_ip = '192.168.0.1'
         self.enable_dhcp = True
+        self.subnetpool_id = FAKE_V4_SUBNETPOOL_ID
 
 
 class FakeV6Subnet(object):
@@ -1753,6 +1757,7 @@ class FakeV6Subnet(object):
         self.cidr = '2001:db8:0:1::/64'
         self.gateway_ip = '2001:db8:0:1::1'
         self.enable_dhcp = True
+        self.subnetpool_id = FAKE_V6_SUBNETPOOL_ID
 
 
 class FakeV4SubnetOutsideGateway(FakeV4Subnet):

neutron/tests/unit/agent/linux/test_dhcp.py

@@ -436,6 +436,7 @@ class FakeV4Subnet(Dictable):
         self.enable_dhcp = True
         self.host_routes = [FakeV4HostRoute()]
         self.dns_nameservers = ['8.8.8.8']
+        self.subnetpool_id = 'kkkkkkkk-kkkk-kkkk-kkkk-kkkkkkkkkkkk'
 
 
 class FakeV4Subnet2(FakeV4Subnet):
@@ -563,6 +564,7 @@ class FakeV6Subnet(object):
         self.dns_nameservers = ['2001:0200:feed:7ac0::1']
         self.ipv6_ra_mode = None
         self.ipv6_address_mode = None
+        self.subnetpool_id = 'jjjjjjjj-jjjj-jjjj-jjjj-jjjjjjjjjjjj'
 
 
 class FakeV4SubnetNoDHCP(object):
@@ -587,6 +589,7 @@ class FakeV6SubnetDHCPStateful(Dictable):
         self.dns_nameservers = ['2001:0200:feed:7ac0::1']
         self.ipv6_ra_mode = None
         self.ipv6_address_mode = constants.DHCPV6_STATEFUL
+        self.subnetpool_id = 'mmmmmmmm-mmmm-mmmm-mmmm-mmmmmmmmmmmm'
 
 
 class FakeV6SubnetSlaac(object):

neutron/tests/unit/db/test_db_base_plugin_v2.py

@@ -3971,8 +3971,9 @@ class TestSubnetsV2(NeutronDbPluginV2TestCase):
                                  ipv6_ra_mode=constants.DHCPV6_STATELESS,
                                  ipv6_address_mode=constants.DHCPV6_STATELESS)
         # If gateway_ip is not specified and the subnet is using prefix
-        # delegation, until the CIDR is assigned, this value should be "None"
+        # delegation, until the CIDR is assigned, this value should be first
-        expected = {'gateway_ip': None,
+        # IP from the subnet
+        expected = {'gateway_ip': str(netaddr.IPNetwork(cidr).network),
                     'cidr': cidr}
         self._test_create_subnet(expected=expected,
                                  cidr=cidr, ip_version=constants.IP_VERSION_6,