nixos/networking: network is online if default gw set

Previously services depending on network-online.target would wait until
dhcpcd times out if it was enabled and a static network address
configuration was used. Setting the default gateway statically is enough
for the networking to be considered online.

This also adjusts the relevant networking tests to wait for
network-online.target instead of just network.target.

nixos/modules/services/networking/dhcpcd.nix

@@ -153,10 +153,14 @@ in
 
   config = mkIf enableDHCP {
 
-    systemd.services.dhcpcd =
+    systemd.services.dhcpcd = let
+      cfgN = config.networking;
+      hasDefaultGatewaySet = (cfgN.defaultGateway != null && cfgN.defaultGateway.address != "")
+                          || (cfgN.defaultGateway6 != null && cfgN.defaultGateway6.address != "");
+    in
       { description = "DHCP Client";
 
-        wantedBy = [ "network-online.target" ];
+        wantedBy = optional (!hasDefaultGatewaySet) "network-online.target";
         after = [ "network.target" ];
         wants = [ "network.target" ];
 

nixos/modules/tasks/network-interfaces-scripted.nix

@@ -73,6 +73,9 @@ let
           then [ "${dev}-netdev.service" ]
           else optional (dev != null && dev != "lo" && !config.boot.isContainer) (subsystemDevice dev);
 
+        hasDefaultGatewaySet = (cfg.defaultGateway != null && cfg.defaultGateway.address != "")
+                            || (cfg.defaultGateway6 != null && cfg.defaultGateway6.address != "");
+
         networkLocalCommands = {
           after = [ "network-setup.service" ];
           bindsTo = [ "network-setup.service" ];
@@ -85,7 +88,7 @@ let
             before = [ "network.target" "shutdown.target" ];
             wants = [ "network.target" ];
             conflicts = [ "shutdown.target" ];
-            wantedBy = [ "multi-user.target" ];
+            wantedBy = [ "multi-user.target" ] ++ optional hasDefaultGatewaySet "network-online.target";
 
             unitConfig.ConditionCapability = "CAP_NET_ADMIN";
 

nixos/tests/networking.nix

@@ -105,7 +105,7 @@ let
           startAll;
 
           $client->waitForUnit("network.target");
-          $router->waitForUnit("network.target");
+          $router->waitForUnit("network-online.target");
 
           # Make sure dhcpcd is not started
           $client->fail("systemctl status dhcpcd.service");
@@ -157,7 +157,7 @@ let
           startAll;
 
           $client->waitForUnit("network.target");
-          $router->waitForUnit("network.target");
+          $router->waitForUnit("network-online.target");
 
           # Wait until we have an ip address on each interface
           $client->waitUntilSucceeds("ip addr show dev eth1 | grep -q '192.168.1'");