working

modules/kboot-conf/default.nix

@@ -0,0 +1,60 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.boot.loader.kboot-conf;
+
+  # The builder used to write during system activation
+  builder = pkgs.substituteAll {
+    src = ./generate-kboot-conf.sh;
+    isExecutable = true;
+    path = [pkgs.coreutils pkgs.gnused pkgs.gnugrep];
+    inherit (pkgs) bash;
+  };
+  # The builder exposed in populateCmd, which runs on the build architecture
+  populateBuilder = pkgs.buildPackages.substituteAll {
+    src = ./generate-kboot-conf.sh;
+    isExecutable = true;
+    path = with pkgs.buildPackages; [coreutils gnused gnugrep];
+    inherit (pkgs.buildPackages) bash;
+  };
+in
+{
+  options = {
+    boot.loader.kboot-conf = {
+      enable = mkOption {
+        default = false;
+        type = types.bool;
+        description = ''
+          Whether to create petitboot-compatible /kboot.conf
+        '';
+      };
+      configurationLimit = mkOption {
+        default = 10;
+        example = 5;
+        type = types.int;
+        description = ''
+          Maximum number of configurations in the generated kboot.conf.
+        '';
+      };
+      populateCmd = mkOption {
+        type = types.str;
+        readOnly = true;
+        description = ''
+          Contains the builder command used to populate an image,
+          honoring all options except the <literal>-c &lt;path-to-default-configuration&gt;</literal>
+          argument.
+          Useful to have for sdImage.populateRootCommands
+        '';
+      };
+    };
+  };
+  config = let
+    args = "-g ${toString cfg.configurationLimit} -n ${config.hardware.deviceTree.name}";
+  in mkIf cfg.enable {
+    system.build.installBootLoader = lib.mkForce "${builder} ${args} -c";
+    system.boot.loader.id = "kboot-conf";
+    boot.loader.kboot-conf.populateCmd = "${populateBuilder} ${args}";
+  };
+}