network: introduce network- and protocol-independent default for UseDomains=

Follow-up for fb57300743.

Prompted by #32273.

src/network/networkd-dns.c

@@ -31,7 +31,7 @@ UseDomains link_get_use_domains(Link *link, NetworkConfigSource proto) {
         case NETWORK_CONFIG_SOURCE_NDISC:
                 n = link->network->ndisc_use_domains;
                 c = _USE_DOMAINS_INVALID;
-                m = _USE_DOMAINS_INVALID;
+                m = link->manager->ndisc_use_domains;
                 break;
         default:
                 assert_not_reached();
@@ -45,12 +45,16 @@ UseDomains link_get_use_domains(Link *link, NetworkConfigSource proto) {
         if (c >= 0)
                 return c;
 
+        /* If per-network but protocol-independent setting is specified, use it. */
+        if (link->network->use_domains >= 0)
+                return link->network->use_domains;
+
         /* If global per-protocol setting is specified, use it. */
         if (m >= 0)
                 return m;
 
-        /* Otherwise, defaults to no. */
-        return USE_DOMAINS_NO;
+        /* If none of them are specified, use the global protocol-independent value. */
+        return link->manager->use_domains;
 }
 
 bool link_get_use_dns(Link *link, NetworkConfigSource proto) {

src/network/networkd-gperf.gperf

@@ -31,6 +31,8 @@ Network.RouteTable,                      config_parse_route_table_names,
 Network.IPv4Forwarding,                  config_parse_tristate,                  0,          offsetof(Manager, ip_forwarding[0])
 Network.IPv6Forwarding,                  config_parse_tristate,                  0,          offsetof(Manager, ip_forwarding[1])
 Network.IPv6PrivacyExtensions,           config_parse_ipv6_privacy_extensions,   0,          offsetof(Manager, ipv6_privacy_extensions)
+Network.UseDomains,                      config_parse_use_domains,               0,          offsetof(Manager, use_domains)
+IPv6AcceptRA.UseDomains,                 config_parse_use_domains,               0,          offsetof(Manager, ndisc_use_domains)
 DHCPv4.UseDomains,                       config_parse_use_domains,               0,          offsetof(Manager, dhcp_use_domains)
 DHCPv4.DUIDType,                         config_parse_duid_type,                 0,          offsetof(Manager, dhcp_duid)
 DHCPv4.DUIDRawData,                      config_parse_duid_rawdata,              0,          offsetof(Manager, dhcp_duid)

src/network/networkd-manager.c

@@ -601,6 +601,7 @@ int manager_new(Manager **ret, bool test_mode) {
                 .persistent_storage_fd = persistent_storage_open(),
                 .dhcp_use_domains = _USE_DOMAINS_INVALID,
                 .dhcp6_use_domains = _USE_DOMAINS_INVALID,
+                .ndisc_use_domains = _USE_DOMAINS_INVALID,
                 .dhcp_duid.type = DUID_TYPE_EN,
                 .dhcp6_duid.type = DUID_TYPE_EN,
                 .duid_product_uuid.type = DUID_TYPE_UUID,

src/network/networkd-manager.h

@@ -64,8 +64,10 @@ struct Manager {
         OrderedSet *address_pools;
         Set *dhcp_pd_subnet_ids;
 
+        UseDomains use_domains; /* default for all protocols */
         UseDomains dhcp_use_domains;
         UseDomains dhcp6_use_domains;
+        UseDomains ndisc_use_domains;
 
         DUID dhcp_duid;
         DUID dhcp6_duid;

src/network/networkd-network-gperf.gperf

@@ -118,6 +118,7 @@ Network.EmitLLDP,                            config_parse_lldp_multicast_mode,
 Network.Address,                             config_parse_address,                                     0,                             0
 Network.Gateway,                             config_parse_gateway,                                     0,                             0
 Network.Domains,                             config_parse_domains,                                     0,                             0
+Network.UseDomains,                          config_parse_use_domains,                                 0,                             offsetof(Network, use_domains)
 Network.DNS,                                 config_parse_dns,                                         0,                             0
 Network.DNSDefaultRoute,                     config_parse_tristate,                                    0,                             offsetof(Network, dns_default_route)
 Network.LLMNR,                               config_parse_resolve_support,                             0,                             offsetof(Network, llmnr)

src/network/networkd-network.c

@@ -377,6 +377,8 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
 
                 .keep_configuration = manager->keep_configuration,
 
+                .use_domains = _USE_DOMAINS_INVALID,
+
                 .compat_dhcp_use_domains = _USE_DOMAINS_INVALID,
                 .compat_dhcp_use_dns = -1,
                 .compat_dhcp_use_ntp = -1,
@@ -489,6 +491,7 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                 .ndisc_use_hop_limit = true,
                 .ndisc_use_reachable_time = true,
                 .ndisc_use_retransmission_time = true,
+                .ndisc_use_domains = _USE_DOMAINS_INVALID,
                 .ndisc_route_table = RT_TABLE_MAIN,
                 .ndisc_route_metric_high = IPV6RA_ROUTE_METRIC_HIGH,
                 .ndisc_route_metric_medium = IPV6RA_ROUTE_METRIC_MEDIUM,

src/network/networkd-network.h

@@ -113,6 +113,9 @@ struct Network {
         bool default_route_on_device;
         AddressFamily ip_masquerade;
 
+        /* Protocol independent settings */
+        UseDomains use_domains;
+
         /* For backward compatibility, only applied to DHCPv4 and DHCPv6. */
         UseDomains compat_dhcp_use_domains;
         int compat_dhcp_use_dns;

src/network/networkd.conf

@@ -24,16 +24,20 @@
 #ManageForeignNextHops=yes
 #RouteTable=
 #IPv6PrivacyExtensions=no
+#UseDomains=no
+
+[IPv6AcceptRA]
+#UseDomains=
 
 [DHCPv4]
 #DUIDType=vendor
 #DUIDRawData=
-#UseDomains=no
+#UseDomains=
 
 [DHCPv6]
 #DUIDType=vendor
 #DUIDRawData=
-#UseDomains=no
+#UseDomains=
 
 [DHCPServer]
 #PersistLeases=yes