use specializations to have multiple kernel versions

hosts/skipper/default.nix

@@ -9,6 +9,7 @@
     ./rollback.nix
     ./secureboot.nix
     ./security.nix
+    ./specialisations.nix
     ./virtualisation.nix
   ];
 

hosts/skipper/hardware/kernel.nix

@@ -18,7 +18,7 @@
       systemd.enable = true;
     };
     kernelModules = [ "kvm-intel" ];
-    kernelPackages = pkgs.linuxPackages_xanmod_latest;
+    kernelPackages = lib.mkDefault pkgs.linuxPackages_latest;
     kernelParams = [ "quiet" ];
     kernel.sysctl = {
       "vm.swappiness" = 10;

hosts/skipper/specialisations.nix

@@ -0,0 +1,25 @@
+{ lib
+, pkgs
+, ...
+}: {
+  specialisation = {
+    xanmod = {
+      inheritParentConfig = true;
+      configuration = {
+        boot = {
+          kernelPackages = lib.mkForce pkgs.linuxPackages_xanmod_latest;
+        };
+        system.nixos.tags = [ "with-xanmod" ];
+      };
+    };
+    zen = {
+      inheritParentConfig = true;
+      configuration = {
+        boot = {
+          kernelPackages = lib.mkForce pkgs.linuxPackages_zen;
+        };
+        system.nixos.tags = [ "with-zen" ];
+      };
+    };
+  };
+}