nixos/wireless: link config to /etc by default

This links the generated configuration to /etc/wpa_supplicant.conf
unless `allowAuxiliaryImperativeNetworks`. In the latter case the
file in /etc should be writable and the generated one remains only
in the Nix store.

nixos/modules/services/networking/wpa_supplicant.nix

@@ -50,15 +50,6 @@ let
     ++ optional cfg.scanOnLowSignal ''bgscan="simple:30:-70:3600"''
     ++ optional (cfg.extraConfig != "") cfg.extraConfig);
 
-  configIsGenerated = with cfg;
-    networks != {} || extraConfig != "" || userControlled.enable;
-
-  # the original configuration file
-  configFile =
-    if configIsGenerated
-      then pkgs.writeText "wpa_supplicant.conf" generatedConfig
-      else "/etc/wpa_supplicant.conf";
-
   # Creates a network block for wpa_supplicant.conf
   mkNetwork = opts:
   let
@@ -90,8 +81,8 @@ let
     let
       deviceUnit = optional (iface != null) "sys-subsystem-net-devices-${utils.escapeSystemdPath iface}.device";
       configStr = if cfg.allowAuxiliaryImperativeNetworks
-        then "-c /etc/wpa_supplicant.conf -I ${configFile}"
-        else "-c ${configFile}";
+        then "-c /etc/wpa_supplicant.conf -I ${pkgs.writeText "wpa_supplicant.conf" generatedConfig}"
+        else "-c /etc/wpa_supplicant.conf";
     in {
       description = "WPA Supplicant instance" + optionalString (iface != null) " for interface ${iface}";
 
@@ -112,12 +103,6 @@ let
 
       script =
       ''
-        ${optionalString (configIsGenerated && !cfg.allowAuxiliaryImperativeNetworks) ''
-          if [ -f /etc/wpa_supplicant.conf ]; then
-            echo >&2 "<3>/etc/wpa_supplicant.conf present but ignored. Generated ${configFile} is used instead."
-          fi
-        ''}
-
         # ensure wpa_supplicant.conf exists, or the daemon will fail to start
         ${optionalString cfg.allowAuxiliaryImperativeNetworks ''
           touch /etc/wpa_supplicant.conf
@@ -531,6 +516,9 @@ in {
 
     hardware.wirelessRegulatoryDatabase = true;
 
+    environment.etc."wpa_supplicant.conf" =
+      lib.mkIf (!cfg.allowAuxiliaryImperativeNetworks) { text = generatedConfig; };
+
     environment.systemPackages = [ pkgs.wpa_supplicant ];
     services.dbus.packages = optional cfg.dbusControlled pkgs.wpa_supplicant;
 

nixos/tests/wpa_supplicant.nix

@@ -123,16 +123,14 @@ in
     };
 
     testScript = ''
+      config_file = "/etc/static/wpa_supplicant.conf"
+
       with subtest("Daemon is running and accepting connections"):
           machine.wait_for_unit("wpa_supplicant.service")
           status = machine.wait_until_succeeds("wpa_cli status")
           assert "Failed to connect" not in status, \
                  "Failed to connect to the daemon"
 
-      # get the configuration file
-      cmdline = machine.succeed("cat /proc/$(pgrep wpa)/cmdline").split('\x00')
-      config_file = cmdline[cmdline.index("-c") + 1]
-
       with subtest("WPA2 fallbacks have been generated"):
           assert int(machine.succeed(f"grep -c sae-only {config_file}")) == 1
           assert int(machine.succeed(f"grep -c mixed-wpa {config_file}")) == 2