iso-image.nix

# This module creates a bootable ISO image containing the given NixOS
# configuration.  The derivation for the ISO image will be placed in
# config.system.build.isoImage.

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

with lib;

let
  /**
   * Given a list of `options`, concats the result of mapping each options
   * to a menuentry for use in grub.
   *
   *  * defaults: {name, image, params, initrd}
   *  * options: [ option... ]
   *  * option: {name, params, class}
   */
  menuBuilderGrub2 =
  defaults: options: lib.concatStrings
    (
      map
      (option: ''
        menuentry '${defaults.name} ${
        # Name appended to menuentry defaults to params if no specific name given.
        option.name or (if option ? params then "(${option.params})" else "")
        }' ${if option ? class then " --class ${option.class}" else ""} {
          linux ${defaults.image} \''${isoboot} ${defaults.params} ${
            option.params or ""
          }
          initrd ${defaults.initrd}
        }
      '')
      options
    )
  ;

  /**
   * Given a `config`, builds the default options.
   */
  buildMenuGrub2 = config:
    buildMenuAdditionalParamsGrub2 config ""
  ;

  /**
   * Given a `config` and params to add to `params`, build a set of default options.
   * Use this one when creating a variant (e.g. hidpi)
   */
  buildMenuAdditionalParamsGrub2 = config: additional:
  let
    finalCfg = {
      name = "NixOS ${config.system.nixos.label}${config.isoImage.appendToMenuLabel}";
      params = "init=${config.system.build.toplevel}/init ${additional} ${toString config.boot.kernelParams}";
      image = "/boot/${config.system.boot.loader.kernelFile}";
      initrd = "/boot/initrd";
    };
  in
    menuBuilderGrub2
    finalCfg
    [
      { class = "installer"; }
      { class = "nomodeset"; params = "nomodeset"; }
      { class = "copytoram"; params = "copytoram"; }
      { class = "debug";     params = "debug"; }
    ]
  ;

  # Timeout in syslinux is in units of 1/10 of a second.
  # 0 is used to disable timeouts.
  syslinuxTimeout = if config.boot.loader.timeout == null then
      0
    else
      max (config.boot.loader.timeout * 10) 1;


  max = x: y: if x > y then x else y;

  # The configuration file for syslinux.

  # Notes on syslinux configuration and UNetbootin compatiblity:
  #   * Do not use '/syslinux/syslinux.cfg' as the path for this
  #     configuration. UNetbootin will not parse the file and use it as-is.
  #     This results in a broken configuration if the partition label does
  #     not match the specified config.isoImage.volumeID. For this reason
  #     we're using '/isolinux/isolinux.cfg'.
  #   * Use APPEND instead of adding command-line arguments directly after
  #     the LINUX entries.
  #   * COM32 entries (chainload, reboot, poweroff) are not recognized. They
  #     result in incorrect boot entries.

  baseIsolinuxCfg = ''
    SERIAL 0 115200
    TIMEOUT ${builtins.toString syslinuxTimeout}
    UI vesamenu.c32
    MENU TITLE NixOS
    MENU BACKGROUND /isolinux/background.png
    MENU RESOLUTION 800 600
    MENU CLEAR
    MENU ROWS 6
    MENU CMDLINEROW -4
    MENU TIMEOUTROW -3
    MENU TABMSGROW  -2
    MENU HELPMSGROW -1
    MENU HELPMSGENDROW -1
    MENU MARGIN 0

    #                                FG:AARRGGBB  BG:AARRGGBB   shadow
    MENU COLOR BORDER       30;44      #00000000    #00000000   none
    MENU COLOR SCREEN       37;40      #FF000000    #00E2E8FF   none
    MENU COLOR TABMSG       31;40      #80000000    #00000000   none
    MENU COLOR TIMEOUT      1;37;40    #FF000000    #00000000   none
    MENU COLOR TIMEOUT_MSG  37;40      #FF000000    #00000000   none
    MENU COLOR CMDMARK      1;36;40    #FF000000    #00000000   none
    MENU COLOR CMDLINE      37;40      #FF000000    #00000000   none
    MENU COLOR TITLE        1;36;44    #00000000    #00000000   none
    MENU COLOR UNSEL        37;44      #FF000000    #00000000   none
    MENU COLOR SEL          7;37;40    #FFFFFFFF    #FF5277C3   std

    DEFAULT boot

    LABEL boot
    MENU LABEL NixOS ${config.system.nixos.label}${config.isoImage.appendToMenuLabel}
    LINUX /boot/${config.system.boot.loader.kernelFile}
    APPEND init=${config.system.build.toplevel}/init ${toString config.boot.kernelParams}
    INITRD /boot/${config.system.boot.loader.initrdFile}

    # A variant to boot with 'nomodeset'
    LABEL boot-nomodeset
    MENU LABEL NixOS ${config.system.nixos.label}${config.isoImage.appendToMenuLabel} (nomodeset)
    LINUX /boot/${config.system.boot.loader.kernelFile}
    APPEND init=${config.system.build.toplevel}/init ${toString config.boot.kernelParams} nomodeset
    INITRD /boot/${config.system.boot.loader.initrdFile}

    # A variant to boot with 'copytoram'
    LABEL boot-copytoram
    MENU LABEL NixOS ${config.system.nixos.label}${config.isoImage.appendToMenuLabel} (copytoram)
    LINUX /boot/${config.system.boot.loader.kernelFile}
    APPEND init=${config.system.build.toplevel}/init ${toString config.boot.kernelParams} copytoram
    INITRD /boot/${config.system.boot.loader.initrdFile}

    # A variant to boot with verbose logging to the console
    LABEL boot-debug
    MENU LABEL NixOS ${config.system.nixos.label}${config.isoImage.appendToMenuLabel} (debug)
    LINUX /boot/${config.system.boot.loader.kernelFile}
    APPEND init=${config.system.build.toplevel}/init ${toString config.boot.kernelParams} loglevel=7
    INITRD /boot/${config.system.boot.loader.initrdFile}
  '';

  isolinuxMemtest86Entry = ''
    LABEL memtest
    MENU LABEL Memtest86+
    LINUX /boot/memtest.bin
    APPEND ${toString config.boot.loader.grub.memtest86.params}
  '';

  isolinuxCfg = concatStringsSep "\n"
    ([ baseIsolinuxCfg ] ++ optional config.boot.loader.grub.memtest86.enable isolinuxMemtest86Entry);

  # Setup instructions for rEFInd.
  refind =
    if targetArch == "x64" then
      ''
      # Adds rEFInd to the ISO.
      cp -v ${pkgs.refind}/share/refind/refind_x64.efi $out/EFI/boot/
      ''
    else
      "# No refind for ${targetArch}"
  ;

  grubPkgs = if config.boot.loader.grub.forcei686 then pkgs.pkgsi686Linux else pkgs;

  grubMenuCfg = ''
    #
    # Menu configuration
    #

    insmod gfxterm
    insmod png
    set gfxpayload=keep

    # Fonts can be loaded?
    # (This font is assumed to always be provided as a fallback by NixOS)
    if loadfont (hd0)/EFI/boot/unicode.pf2; then
      # Use graphical term, it can be either with background image or a theme.
      # input is "console", while output is "gfxterm".
      # This enables "serial" input and output only when possible.
      # Otherwise the failure mode is to not even enable gfxterm.
      if test "\$with_serial" == "yes"; then
        terminal_output gfxterm serial
        terminal_input  console serial
      else
        terminal_output gfxterm
        terminal_input  console
      fi
    else
      # Sets colors for the non-graphical term.
      set menu_color_normal=cyan/blue
      set menu_color_highlight=white/blue
    fi

    ${ # When there is a theme configured, use it, otherwise use the background image.
    if config.isoImage.grubTheme != null then ''
      # Sets theme.
      set theme=(hd0)/EFI/boot/grub-theme/theme.txt
      # Load theme fonts
      $(find ${config.isoImage.grubTheme} -iname '*.pf2' -printf "loadfont (hd0)/EFI/boot/grub-theme/%P\n")
    '' else ''
      if background_image (hd0)/EFI/boot/efi-background.png; then
        # Black background means transparent background when there
        # is a background image set... This seems undocumented :(
        set color_normal=black/black
        set color_highlight=white/blue
      else
        # Falls back again to proper colors.
        set menu_color_normal=cyan/blue
        set menu_color_highlight=white/blue
      fi
    ''}
  '';

  # The EFI boot image.
  # Notes about grub:
  #  * Yes, the grubMenuCfg has to be repeated in all submenus. Otherwise you
  #    will get white-on-black console-like text on sub-menus. *sigh*
  efiDir = pkgs.runCommand "efi-directory" {} ''
    mkdir -p $out/EFI/boot/

    # ALWAYS required modules.
    MODULES="fat iso9660 part_gpt part_msdos \
             normal boot linux configfile loopback chain halt \
             efifwsetup efi_gop \
             ls search search_label search_fs_uuid search_fs_file \
             gfxmenu gfxterm gfxterm_background gfxterm_menu test all_video loadenv \
             exfat ext2 ntfs btrfs hfsplus udf \
             videoinfo png \
             echo serial \
            "

    echo "Building GRUB with modules:"
    for mod in $MODULES; do
      echo " - $mod"
    done

    # Modules that may or may not be available per-platform.
    echo "Adding additional modules:"
    for mod in efi_uga; do
      if [ -f ${grubPkgs.grub2_efi}/lib/grub/${grubPkgs.grub2_efi.grubTarget}/$mod.mod ]; then
        echo " - $mod"
        MODULES+=" $mod"
      fi
    done

    # Make our own efi program, we can't rely on "grub-install" since it seems to
    # probe for devices, even with --skip-fs-probe.
    ${grubPkgs.grub2_efi}/bin/grub-mkimage -o $out/EFI/boot/boot${targetArch}.efi -p /EFI/boot -O ${grubPkgs.grub2_efi.grubTarget} \
      $MODULES
    cp ${grubPkgs.grub2_efi}/share/grub/unicode.pf2 $out/EFI/boot/

    cat <<EOF > $out/EFI/boot/grub.cfg

    # If you want to use serial for "terminal_*" commands, you need to set one up:
    #   Example manual configuration:
    #    → serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
    # This uses the defaults, and makes the serial terminal available.
    set with_serial=no
    if serial; then set with_serial=yes ;fi
    export with_serial
    clear
    set timeout=10
    ${grubMenuCfg}

    # If the parameter iso_path is set, append the findiso parameter to the kernel
    # line. We need this to allow the nixos iso to be booted from grub directly.
    if [ \''${iso_path} ] ; then
      set isoboot="findiso=\''${iso_path}"
    fi

    #
    # Menu entries
    #

    ${buildMenuGrub2 config}
    submenu "HiDPI, Quirks and Accessibility" --class hidpi --class submenu {
      ${grubMenuCfg}
      submenu "Suggests resolution @720p" --class hidpi-720p {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "video=1280x720@60"}
      }
      submenu "Suggests resolution @1080p" --class hidpi-1080p {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "video=1920x1080@60"}
      }

      # If we boot into a graphical environment where X is autoran
      # and always crashes, it makes the media unusable. Allow the user
      # to disable this.
      submenu "Disable display-manager" --class quirk-disable-displaymanager {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "systemd.mask=display-manager.service"}
      }

      # Some laptop and convertibles have the panel installed in an
      # inconvenient way, rotated away from the keyboard.
      # Those entries makes it easier to use the installer.
      submenu "" {return}
      submenu "Rotate framebuffer Clockwise" --class rotate-90cw {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "fbcon=rotate:1"}
      }
      submenu "Rotate framebuffer Upside-Down" --class rotate-180 {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "fbcon=rotate:2"}
      }
      submenu "Rotate framebuffer Counter-Clockwise" --class rotate-90ccw {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "fbcon=rotate:3"}
      }

      # As a proof of concept, mainly. (Not sure it has accessibility merits.)
      submenu "" {return}
      submenu "Use black on white" --class accessibility-blakconwhite {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "vt.default_red=0xFF,0xBC,0x4F,0xB4,0x56,0xBC,0x4F,0x00,0xA1,0xCF,0x84,0xCA,0x8D,0xB4,0x84,0x68 vt.default_grn=0xFF,0x55,0xBA,0xBA,0x4D,0x4D,0xB3,0x00,0xA0,0x8F,0xB3,0xCA,0x88,0x93,0xA4,0x68 vt.default_blu=0xFF,0x58,0x5F,0x58,0xC5,0xBD,0xC5,0x00,0xA8,0xBB,0xAB,0x97,0xBD,0xC7,0xC5,0x68"}
      }

      # Serial access is a must!
      submenu "" {return}
      submenu "Serial console=ttyS0,115200n8" --class serial {
        ${grubMenuCfg}
        ${buildMenuAdditionalParamsGrub2 config "console=ttyS0,115200n8"}
      }
    }

    menuentry 'rEFInd' --class refind {
      # UUID is hard-coded in the derivation.
      search --set=root --no-floppy --fs-uuid 1234-5678
      chainloader (\$root)/EFI/boot/refind_x64.efi
    }
    menuentry 'Firmware Setup' --class settings {
      fwsetup
      clear
      echo ""
      echo "If you see this message, your EFI system doesn't support this feature."
      echo ""
    }
    menuentry 'Shutdown' --class shutdown {
      halt
    }
    EOF

    ${refind}
  '';

  efiImg = pkgs.runCommand "efi-image_eltorito" { buildInputs = [ pkgs.mtools pkgs.libfaketime ]; }
    # Be careful about determinism: du --apparent-size,
    #   dates (cp -p, touch, mcopy -m, faketime for label), IDs (mkfs.vfat -i)
    ''
      mkdir ./contents && cd ./contents
      cp -rp "${efiDir}"/EFI .
      mkdir ./boot
      cp -p "${config.boot.kernelPackages.kernel}/${config.system.boot.loader.kernelFile}" \
        "${config.system.build.initialRamdisk}/${config.system.boot.loader.initrdFile}" ./boot/
      touch --date=@0 ./EFI ./boot

      usage_size=$(du -sb --apparent-size . | tr -cd '[:digit:]')
      # Make the image 110% as big as the files need to make up for FAT overhead
      image_size=$(( ($usage_size * 110) / 100 ))
      # Make the image fit blocks of 1M
      block_size=$((1024*1024))
      image_size=$(( ($image_size / $block_size + 1) * $block_size ))
      echo "Usage size: $usage_size"
      echo "Image size: $image_size"
      truncate --size=$image_size "$out"
      ${pkgs.libfaketime}/bin/faketime "2000-01-01 00:00:00" ${pkgs.dosfstools}/sbin/mkfs.vfat -i 12345678 -n EFIBOOT "$out"
      mcopy -psvm -i "$out" ./EFI ./boot ::
      # Verify the FAT partition.
      ${pkgs.dosfstools}/sbin/fsck.vfat -vn "$out"
    ''; # */

  # Name used by UEFI for architectures.
  targetArch =
    if pkgs.stdenv.isi686 || config.boot.loader.grub.forcei686 then
      "ia32"
    else if pkgs.stdenv.isx86_64 then
      "x64"
    else if pkgs.stdenv.isAarch64 then
      "aa64"
    else
      throw "Unsupported architecture";

  # Syslinux (and isolinux) only supports x86-based architectures.
  canx86BiosBoot = pkgs.stdenv.isi686 || pkgs.stdenv.isx86_64;

in

{
  options = {

    isoImage.isoName = mkOption {
      default = "${config.isoImage.isoBaseName}.iso";
      description = ''
        Name of the generated ISO image file.
      '';
    };

    isoImage.isoBaseName = mkOption {
      default = "nixos";
      description = ''
        Prefix of the name of the generated ISO image file.
      '';
    };

    isoImage.compressImage = mkOption {
      default = false;
      description = ''
        Whether the ISO image should be compressed using
        <command>bzip2</command>.
      '';
    };

    isoImage.edition = mkOption {
      default = "";
      description = ''
        Specifies which edition string to use in the volume ID of the generated
        ISO image.
      '';
    };

    isoImage.volumeID = mkOption {
      # nixos-$EDITION-$RELEASE-$ARCH
      default = "nixos${optionalString (config.isoImage.edition != "") "-${config.isoImage.edition}"}-${config.system.nixos.release}-${pkgs.stdenv.hostPlatform.system}";
      description = ''
        Specifies the label or volume ID of the generated ISO image.
        Note that the label is used by stage 1 of the boot process to
        mount the CD, so it should be reasonably distinctive.
      '';
    };

    isoImage.contents = mkOption {
      example = literalExample ''
        [ { source = pkgs.memtest86 + "/memtest.bin";
            target = "boot/memtest.bin";
          }
        ]
      '';
      description = ''
        This option lists files to be copied to fixed locations in the
        generated ISO image.
      '';
    };

    isoImage.storeContents = mkOption {
      example = literalExample "[ pkgs.stdenv ]";
      description = ''
        This option lists additional derivations to be included in the
        Nix store in the generated ISO image.
      '';
    };

    isoImage.includeSystemBuildDependencies = mkOption {
      default = false;
      description = ''
        Set this option to include all the needed sources etc in the
        image. It significantly increases image size. Use that when
        you want to be able to keep all the sources needed to build your
        system or when you are going to install the system on a computer
        with slow or non-existent network connection.
      '';
    };

    isoImage.makeEfiBootable = mkOption {
      default = false;
      description = ''
        Whether the ISO image should be an efi-bootable volume.
      '';
    };

    isoImage.makeUsbBootable = mkOption {
      default = false;
      description = ''
        Whether the ISO image should be bootable from CD as well as USB.
      '';
    };

    isoImage.efiSplashImage = mkOption {
      default = pkgs.fetchurl {
          url = https://raw.githubusercontent.com/NixOS/nixos-artwork/a9e05d7deb38a8e005a2b52575a3f59a63a4dba0/bootloader/efi-background.png;
          sha256 = "18lfwmp8yq923322nlb9gxrh5qikj1wsk6g5qvdh31c4h5b1538x";
        };
      description = ''
        The splash image to use in the EFI bootloader.
      '';
    };

    isoImage.splashImage = mkOption {
      default = pkgs.fetchurl {
          url = https://raw.githubusercontent.com/NixOS/nixos-artwork/a9e05d7deb38a8e005a2b52575a3f59a63a4dba0/bootloader/isolinux/bios-boot.png;
          sha256 = "1wp822zrhbg4fgfbwkr7cbkr4labx477209agzc0hr6k62fr6rxd";
        };
      description = ''
        The splash image to use in the legacy-boot bootloader.
      '';
    };

    isoImage.grubTheme = mkOption {
      default = pkgs.nixos-grub2-theme;
      type = types.nullOr (types.either types.path types.package);
      description = ''
        The grub2 theme used for UEFI boot.
      '';
    };

    isoImage.appendToMenuLabel = mkOption {
      default = " Installer";
      example = " Live System";
      description = ''
        The string to append after the menu label for the NixOS system.
        This will be directly appended (without whitespace) to the NixOS version
        string, like for example if it is set to <literal>XXX</literal>:

        <para><literal>NixOS 99.99-pre666XXX</literal></para>
      '';
    };

  };

  config = {
    assertions = [
      {
        assertion = !(stringLength config.isoImage.volumeID > 32);
        # https://wiki.osdev.org/ISO_9660#The_Primary_Volume_Descriptor
        # Volume Identifier can only be 32 bytes
        message = let
          length = stringLength config.isoImage.volumeID;
          howmany = toString length;
          toomany = toString (length - 32);
        in
        "isoImage.volumeID ${config.isoImage.volumeID} is ${howmany} characters. That is ${toomany} characters longer than the limit of 32.";
      }
    ];

    boot.loader.grub.version = 2;

    # Don't build the GRUB menu builder script, since we don't need it
    # here and it causes a cyclic dependency.
    boot.loader.grub.enable = false;

    environment.systemPackages =  [ grubPkgs.grub2 grubPkgs.grub2_efi ]
      ++ optional canx86BiosBoot pkgs.syslinux
    ;

    # In stage 1 of the boot, mount the CD as the root FS by label so
    # that we don't need to know its device.  We pass the label of the
    # root filesystem on the kernel command line, rather than in
    # `fileSystems' below.  This allows CD-to-USB converters such as
    # UNetbootin to rewrite the kernel command line to pass the label or
    # UUID of the USB stick.  It would be nicer to write
    # `root=/dev/disk/by-label/...' here, but UNetbootin doesn't
    # recognise that.
    boot.kernelParams =
      [ "root=LABEL=${config.isoImage.volumeID}"
        "boot.shell_on_fail"
      ];

    fileSystems."/" =
      { fsType = "tmpfs";
        options = [ "mode=0755" ];
      };

    # Note that /dev/root is a symlink to the actual root device
    # specified on the kernel command line, created in the stage 1
    # init script.
    fileSystems."/iso" =
      { device = "/dev/root";
        neededForBoot = true;
        noCheck = true;
      };

    # In stage 1, mount a tmpfs on top of /nix/store (the squashfs
    # image) to make this a live CD.
    fileSystems."/nix/.ro-store" =
      { fsType = "squashfs";
        device = "/iso/nix-store.squashfs";
        options = [ "loop" ];
        neededForBoot = true;
      };

    fileSystems."/nix/.rw-store" =
      { fsType = "tmpfs";
        options = [ "mode=0755" ];
        neededForBoot = true;
      };

    fileSystems."/nix/store" =
      { fsType = "overlay";
        device = "overlay";
        options = [
          "lowerdir=/nix/.ro-store"
          "upperdir=/nix/.rw-store/store"
          "workdir=/nix/.rw-store/work"
        ];
      };

    boot.initrd.availableKernelModules = [ "squashfs" "iso9660" "uas" "overlay" ];

    boot.initrd.kernelModules = [ "loop" "overlay" ];

    # Closures to be copied to the Nix store on the CD, namely the init
    # script and the top-level system configuration directory.
    isoImage.storeContents =
      [ config.system.build.toplevel ] ++
      optional config.isoImage.includeSystemBuildDependencies
        config.system.build.toplevel.drvPath;

    # Create the squashfs image that contains the Nix store.
    system.build.squashfsStore = pkgs.callPackage ../../../lib/make-squashfs.nix {
      storeContents = config.isoImage.storeContents;
    };

    # Individual files to be included on the CD, outside of the Nix
    # store on the CD.
    isoImage.contents =
      [
        { source = config.boot.kernelPackages.kernel + "/" + config.system.boot.loader.kernelFile;
          target = "/boot/" + config.system.boot.loader.kernelFile;
        }
        { source = config.system.build.initialRamdisk + "/" + config.system.boot.loader.initrdFile;
          target = "/boot/" + config.system.boot.loader.initrdFile;
        }
        { source = config.system.build.squashfsStore;
          target = "/nix-store.squashfs";
        }
        { source = config.isoImage.splashImage;
          target = "/isolinux/background.png";
        }
        { source = pkgs.writeText "version" config.system.nixos.label;
          target = "/version.txt";
        }
      ] ++ optionals canx86BiosBoot [
        { source = pkgs.substituteAll  {
            name = "isolinux.cfg";
            src = pkgs.writeText "isolinux.cfg-in" isolinuxCfg;
            bootRoot = "/boot";
          };
          target = "/isolinux/isolinux.cfg";
        }
        { source = "${pkgs.syslinux}/share/syslinux";
          target = "/isolinux";
        }
      ] ++ optionals config.isoImage.makeEfiBootable [
        { source = efiImg;
          target = "/boot/efi.img";
        }
        { source = "${efiDir}/EFI";
          target = "/EFI";
        }
        { source = (pkgs.writeTextDir "grub/loopback.cfg" "source /EFI/boot/grub.cfg") + "/grub";
          target = "/boot/grub";
        }
      ] ++ optionals (config.boot.loader.grub.memtest86.enable && canx86BiosBoot) [
        { source = "${pkgs.memtest86plus}/memtest.bin";
          target = "/boot/memtest.bin";
        }
      ] ++ optionals (config.isoImage.grubTheme != null) [
        { source = config.isoImage.grubTheme;
          target = "/EFI/boot/grub-theme";
        }
      ] ++ [
        { source = config.isoImage.efiSplashImage;
          target = "/EFI/boot/efi-background.png";
        }
      ];

    boot.loader.timeout = 10;

    # Create the ISO image.
    system.build.isoImage = pkgs.callPackage ../../../lib/make-iso9660-image.nix ({
      inherit (config.isoImage) isoName compressImage volumeID contents;
      bootable = canx86BiosBoot;
      bootImage = "/isolinux/isolinux.bin";
      syslinux = if canx86BiosBoot then pkgs.syslinux else null;
    } // optionalAttrs (config.isoImage.makeUsbBootable && canx86BiosBoot) {
      usbBootable = true;
      isohybridMbrImage = "${pkgs.syslinux}/share/syslinux/isohdpfx.bin";
    } // optionalAttrs config.isoImage.makeEfiBootable {
      efiBootable = true;
      efiBootImage = "boot/efi.img";
    });

    boot.postBootCommands =
      ''
        # After booting, register the contents of the Nix store on the
        # CD in the Nix database in the tmpfs.
        ${config.nix.package.out}/bin/nix-store --load-db < /nix/store/nix-path-registration

        # nixos-rebuild also requires a "system" profile and an
        # /etc/NIXOS tag.
        touch /etc/NIXOS
        ${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system
      '';

    # Add vfat support to the initrd to enable people to copy the
    # contents of the CD to a bootable USB stick.
    boot.initrd.supportedFilesystems = [ "vfat" ];

  };

}