nixpkgs/modules/system/activation/top-level.nix

{pkgs, config, modules, baseModules, ...}:

let

  options = {
  
    system.build = pkgs.lib.mkOption {
      default = {};
      description = ''
        Attribute set of derivations used to setup the system.
      '';
    };

    nesting.children = pkgs.lib.mkOption {
      default = [];
      description = ''
        Additional configurations to build.
      '';
    };

    nesting.clone = pkgs.lib.mkOption {
      default = [];
      description = ''
        Additional configurations to build based on the current
        configuration which is has a lower priority.
      '';
    };

    system.boot.loader.id = pkgs.lib.mkOption {
      default = "";
      description = ''
        Id string of the used bootloader.
      '';
    };

    system.boot.loader.kernelFile = pkgs.lib.mkOption {
      default = "";
      description = ''
        Name of the kernel file to be passed to the bootloader.
      '';
    };

    system.copySystemConfiguration = pkgs.lib.mkOption {
      default = false;
      description = ''
        If enabled, copies the NixOS configuration file
        <literal>$NIXOS_CONFIG</literal> (usually
        <filename>/etc/nixos/configuration.nix</filename>)
        to the system store path.
      '';
    };

    system.extraSystemBuilderCmds = pkgs.lib.mkOption {
      default = "";
      internal = true;
      merge = pkgs.lib.concatStringsSep "\n";
      description = ''
        This code will be added to the builder creating the system store path.
      '';
    };
    
  };

    
  # This attribute is responsible for creating boot entries for 
  # child configuration. They are only (directly) accessible
  # when the parent configuration is boot default. For example,
  # you can provide an easy way to boot the same configuration 
  # as you use, but with another kernel
  # !!! fix this
  cloner = inheritParent: list: with pkgs.lib;
    map (childConfig:
      (import ../../../lib/eval-config.nix {
        inherit baseModules;
        modules =
           (optionals inheritParent modules)
        ++ [ ./no-clone.nix ]
        ++ [ childConfig ];
      }).config.system.build.toplevel
    ) list;

  children =
     cloner false config.nesting.children
  ++ cloner true config.nesting.clone;


  systemBuilder =
    let
      kernelPath = "${config.boot.kernelPackages.kernel}/" +
        "${config.system.boot.loader.kernelFile}";
    in ''
      ensureDir $out

      if [ ! -f ${kernelPath} ]; then
        echo "The bootloader cannot find the proper kernel image."
        echo "(Expecting ${kernelPath})"
        false
      fi

      ln -s ${kernelPath} $out/kernel
      ln -s ${config.system.modulesTree} $out/kernel-modules
      if [ -n "$grub" ]; then 
        ln -s $grub $out/grub
      fi
      
      ln -s ${config.system.build.bootStage2} $out/init
      ln -s ${config.system.build.initialRamdisk}/initrd $out/initrd
      
      echo "$activationScript" > $out/activate
      substituteInPlace $out/activate --subst-var out
      chmod u+x $out/activate
      unset activationScript
      
      ln -s ${config.system.build.etc}/etc $out/etc
      ln -s ${config.system.path} $out/sw
      ln -s ${config.system.build.upstart} $out/upstart
      ln -s ${config.hardware.firmware} $out/firmware

      echo "$kernelParams" > $out/kernel-params
      echo "$configurationName" > $out/configuration-name
      echo "${toString config.system.build.upstart.interfaceVersion}" > $out/upstart-interface-version

      mkdir $out/fine-tune
      childCount=0;
      for i in $children; do
        childCount=$(( childCount + 1 ));
        ln -s $i $out/fine-tune/child-$childCount;
      done

      ensureDir $out/bin
      substituteAll ${./switch-to-configuration.sh} $out/bin/switch-to-configuration
      chmod +x $out/bin/switch-to-configuration

      ${config.system.extraSystemBuilderCmds}
    '';

  
  # Putting it all together.  This builds a store path containing
  # symlinks to the various parts of the built configuration (the
  # kernel, the Upstart services, the init scripts, etc.) as well as a
  # script `switch-to-configuration' that activates the configuration
  # and makes it bootable.
  system = pkgs.stdenv.mkDerivation {
    name = "system";
    buildCommand = systemBuilder;
    inherit children;
    kernelParams =
      config.boot.kernelParams ++ config.boot.extraKernelParams;
    menuBuilder = config.system.build.menuBuilder;
    initScriptBuilder = config.system.build.initScriptBuilder;
    activationScript = config.system.activationScripts.script;
    # Most of these are needed by grub-install.
    path = [
      pkgs.coreutils
      pkgs.gnused
      pkgs.gnugrep
      pkgs.findutils
      pkgs.diffutils
      config.system.build.upstart # for initctl
    ];

    # Boot loaders
    bootLoader = config.system.boot.loader.id;
    grub =
      if config.boot.loader.grub.enable
      then config.system.build.grub
      else null;
    grubVersion = 
      if config.boot.loader.grub.enable
      then (builtins.parseDrvName config.system.build.grub.name).version
      else "";
    grubDevice = config.boot.loader.grub.device;
    configurationName = config.boot.loader.grub.configurationName;
  };


in {
  require = [options];

  system.extraSystemBuilderCmds =
    pkgs.lib.optionalString
      config.system.copySystemConfiguration
      "cp ${pkgs.lib.maybeEnv "NIXOS_CONFIG" "/etc/nixos/configuration.nix"} $out";

  system.build.toplevel = system;
}