irqbalance: using systemd service definition from the package itself

nixos/modules/services/hardware/irqbalance.nix

···
 
   config = mkIf cfg.enable {
 
-    systemd.services = {
-      irqbalance = {
-        description = "irqbalance daemon";
-        path = [ pkgs.irqbalance ];
-        serviceConfig = {
-          ExecStart = "${pkgs.irqbalance}/bin/irqbalance --foreground";
-          CapabilityBoundingSet = "";
-          NoNewPrivileges = "yes";
-          ReadOnlyPaths = "/";
-          ReadWritePaths = "/proc/irq";
-          RestrictAddressFamilies = "AF_UNIX";
-          RuntimeDirectory = "irqbalance/";
-        };
-        wantedBy = [ "multi-user.target" ];
-      };
-    };
+    environment.systemPackages = [ pkgs.irqbalance ];
 
-    environment.systemPackages = [ pkgs.irqbalance ];
+    systemd.packages = [ pkgs.irqbalance ];
 
   };
 

pkgs/os-specific/linux/irqbalance/default.nix

···
 
   LDFLAGS = "-lncurses";
 
+  postInstall =
+    ''
+      # Systemd service
+      mkdir -p $out/lib/systemd/system
+      grep -vi "EnvironmentFile" misc/irqbalance.service >$out/lib/systemd/system/irqbalance.service
+      substituteInPlace $out/lib/systemd/system/irqbalance.service \
+        --replace /usr/sbin/irqbalance $out/bin/irqbalance \
+        --replace ' $IRQBALANCE_ARGS' ""
+    '';
+
   meta = {
     homepage = https://github.com/Irqbalance/irqbalance;
     description = "A daemon to help balance the cpu load generated by interrupts across all of a systems cpus";