nm: Find interfaces with default gateway for DNS configuration

Find interfaces with IPv4/IPv6 default gateway for desired DNS
configuration via `nm.dns.find_interfaces_for_dns_conf()`.

Introduce `nm.dns.DNS_PRIORITY_STATIC_BASE` for the DNS priority
on the first name server, the dns priority for remaining name server
could be increase 1 from it.

Signed-off-by: Gris Ge <fge@redhat.com>

libnmstate/nm/dns.py

@@ -21,7 +21,9 @@ from libnmstate import iplib
 from libnmstate.error import NmstateInternalError
 from libnmstate.nm import nmclient
 from libnmstate.nm import active_connection as nm_ac
+from libnmstate.nm import route as nm_route
 from libnmstate.schema import DNS
+from libnmstate.schema import Interface
 
 
 DNS_DEFAULT_PRIORITY_VPN = 50
@@ -29,6 +31,9 @@ DNS_DEFAULT_PRIORITY_OTHER = 100
 DNS_METADATA = '_dns'
 DNS_METADATA_PRIORITY = '_priority'
 DEFAULT_DNS_PRIORITY = 0
+# The 40 is chose as default DHCP DNS priority is 100, and VPN DNS priority is
+# 50, the static DNS configuration should be list before them.
+DNS_PRIORITY_STATIC_BASE = 40
 
 IPV6_ADDRESS_LENGTH = 128
 
@@ -118,3 +123,14 @@ def get_dns_config_iface_names(acs_and_ipv4_profiles, acs_and_ipv6_profiles):
         if ip_profile.props.dns or ip_profile.props.dns_search:
             iface_names.append(nm_ac.ActiveConnection(ac).devname)
     return iface_names
+
+
+def find_interfaces_for_name_servers(iface_routes):
+    """
+    Find interfaces to store the DNS configurations:
+        * Interface with static gateway configured.
+    Return two interface names for IPv4 and IPv6 name servers.
+    The interface name will be None if failed to find proper interface.
+    """
+    return (nm_route.get_static_gateway_iface(Interface.IPV4, iface_routes),
+            nm_route.get_static_gateway_iface(Interface.IPV6, iface_routes))

libnmstate/nm/route.py

@@ -18,11 +18,14 @@
 from operator import itemgetter
 import socket
 
+import six
+
 from libnmstate import iplib
 from libnmstate.error import NmstateInternalError
 from libnmstate.error import NmstateNotImplementedError
 from libnmstate.nm import nmclient
 from libnmstate.nm import active_connection as nm_ac
+from libnmstate.schema import Interface
 from libnmstate.schema import Route
 
 NM_ROUTE_TABLE_ATTRIBUTE = 'table'
@@ -178,3 +181,18 @@ def _add_route_gateway(setting_ip, route):
                                              Route.USE_DEFAULT_ROUTE_TABLE)
     setting_ip.props.route_metric = route.get(Route.METRIC,
                                               Route.USE_DEFAULT_METRIC)
+
+
+def get_static_gateway_iface(family, iface_routes):
+    """
+    Return one interface with gateway for given IP family.
+    Return None if not found.
+    """
+    destination = (IPV6_DEFAULT_GATEWAY_DESTINATION
+                   if family == Interface.IPV6
+                   else IPV4_DEFAULT_GATEWAY_DESTINATION)
+    for iface_name, routes in six.viewitems(iface_routes):
+        for route in routes:
+            if route[Route.DESTINATION] == destination:
+                return iface_name
+    return None

tests/lib/nm/dns_test.py

@@ -17,11 +17,17 @@
 
 import pytest
 
-from libnmstate.schema import DNS
 import libnmstate.nm.connection as nm_connection
 import libnmstate.nm.dns as nm_dns
 import libnmstate.nm.ipv4 as nm_ipv4
 import libnmstate.nm.ipv6 as nm_ipv6
+from libnmstate.schema import DNS
+from libnmstate.schema import Route
+
+
+TEST_IPV4_GATEWAY_IFACE = 'eth1'
+TEST_IPV6_GATEWAY_IFACE = 'eth2'
+TEST_STATIC_ROUTE_IFACE = 'eth3'
 
 
 def _get_test_dns_v4():
@@ -124,3 +130,88 @@ def _assert_dns(setting_ip, dns_conf):
     priority = dns_conf.get(nm_dns.DNS_METADATA_PRIORITY,
                             nm_dns.DEFAULT_DNS_PRIORITY)
     assert setting_ip.props.dns_priority == priority
+
+
+def test_find_interfaces_for_dns_with_ipv6_and_ipv4_static_gateways():
+    iface_routes = _get_test_iface_routes()
+    assert ((TEST_IPV4_GATEWAY_IFACE, TEST_IPV6_GATEWAY_IFACE) ==
+            nm_dns.find_interfaces_for_name_servers(iface_routes))
+
+
+def test_find_interfaces_for_dns_with_ipv6_static_gateway_only():
+    iface_routes = {
+        TEST_IPV6_GATEWAY_IFACE: _get_test_ipv6_gateway(),
+        TEST_STATIC_ROUTE_IFACE: _get_test_static_routes()
+    }
+    assert ((None, TEST_IPV6_GATEWAY_IFACE) ==
+            nm_dns.find_interfaces_for_name_servers(iface_routes))
+
+
+def test_find_interfaces_for_dns_with_ipv4_static_gateway_only():
+    iface_routes = {
+        TEST_IPV4_GATEWAY_IFACE: _get_test_ipv4_gateway(),
+        TEST_STATIC_ROUTE_IFACE: _get_test_static_routes()
+    }
+    assert ((TEST_IPV4_GATEWAY_IFACE, None) ==
+            nm_dns.find_interfaces_for_name_servers(iface_routes))
+
+
+def test_find_interfaces_for_dns_with_no_routes():
+    iface_routes = {}
+    assert ((None, None) ==
+            nm_dns.find_interfaces_for_name_servers(iface_routes))
+
+
+def test_find_interfaces_for_dns_with_no_gateway():
+    iface_routes = {
+        TEST_STATIC_ROUTE_IFACE: _get_test_static_routes()
+    }
+    assert ((None, None) ==
+            nm_dns.find_interfaces_for_name_servers(iface_routes))
+
+
+def _get_test_ipv4_gateway():
+    return [{
+        Route.DESTINATION: '0.0.0.0/0',
+        Route.METRIC: 200,
+        Route.NEXT_HOP_ADDRESS: '192.0.2.1',
+        Route.NEXT_HOP_INTERFACE: TEST_IPV4_GATEWAY_IFACE,
+        Route.TABLE_ID: 54
+    }]
+
+
+def _get_test_ipv6_gateway():
+    return [{
+        Route.DESTINATION: '::/0',
+        Route.METRIC: 201,
+        Route.NEXT_HOP_ADDRESS: '2001:db8:2::f',
+        Route.NEXT_HOP_INTERFACE: TEST_IPV6_GATEWAY_IFACE,
+        Route.TABLE_ID: 54
+    }]
+
+
+def _get_test_static_routes():
+    return [
+        {
+            Route.DESTINATION: '2001:db8:3::1',
+            Route.METRIC: 201,
+            Route.NEXT_HOP_ADDRESS: '2001:db8:2::f',
+            Route.NEXT_HOP_INTERFACE: TEST_STATIC_ROUTE_IFACE,
+            Route.TABLE_ID: 54
+        },
+        {
+            Route.DESTINATION: '198.51.100.0/24',
+            Route.METRIC: 201,
+            Route.NEXT_HOP_ADDRESS: '192.0.2.1',
+            Route.NEXT_HOP_INTERFACE: TEST_STATIC_ROUTE_IFACE,
+            Route.TABLE_ID: 54
+        }
+    ]
+
+
+def _get_test_iface_routes():
+    return {
+        TEST_IPV4_GATEWAY_IFACE: _get_test_ipv4_gateway(),
+        TEST_IPV6_GATEWAY_IFACE: _get_test_ipv6_gateway(),
+        TEST_STATIC_ROUTE_IFACE: _get_test_static_routes(),
+    }