nixpkgs/nixos/modules/system/boot/loader/generic-extlinux-compatible/default.nix

{ config, lib, pkgs, ... }:

with lib;

let
  blCfg = config.boot.loader;
  dtCfg = config.hardware.deviceTree;
  cfg = blCfg.generic-extlinux-compatible;

  timeoutStr = if blCfg.timeout == null then "-1" else toString blCfg.timeout;

  # The builder used to write during system activation
  builder = import ./extlinux-conf-builder.nix { inherit pkgs; };
  # The builder exposed in populateCmd, which runs on the build architecture
  populateBuilder = import ./extlinux-conf-builder.nix { pkgs = pkgs.buildPackages; };
in
{
  options = {
    boot.loader.generic-extlinux-compatible = {
      enable = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether to generate an extlinux-compatible configuration file
          under <literal>/boot/extlinux.conf</literal>.  For instance,
          U-Boot's generic distro boot support uses this file format.

          See <link xlink:href="http://git.denx.de/?p=u-boot.git;a=blob;f=doc/README.distro;hb=refs/heads/master">U-boot's documentation</link>
          for more information.
        '';
      };

      configurationLimit = mkOption {
        default = 20;
        example = 10;
        type = types.int;
        description = ''
          Maximum number of configurations in the boot menu.
        '';
      };

      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
    builderArgs = "-g ${toString cfg.configurationLimit} -t ${timeoutStr}" + lib.optionalString (dtCfg.name != null) " -n ${dtCfg.name}";
  in
    mkIf cfg.enable {
      system.build.installBootLoader = "${builder} ${builderArgs} -c";
      system.boot.loader.id = "generic-extlinux-compatible";

      boot.loader.generic-extlinux-compatible.populateCmd = "${populateBuilder} ${builderArgs}";
    };
}