refind-nixos-module

refind-builder.py

#! @python3@/bin/python3 -B
import argparse
import os
import os.path
import sys
import errno
import subprocess
import glob
import datetime
import shutil
import ctypes
libc = ctypes.CDLL("libc.so.6")

extra_config = '''
@extraConfig@
'''


def mkdir_p(path):
    try:
        os.makedirs(path)
    except OSError as e:
        if e.errno != errno.EEXIST or not os.path.isdir(path):
            raise


def system_dir(profile, generation):
    if profile:
        return "/nix/var/nix/profiles/system-profiles/%s-%d-link" % (profile, generation)
    return "/nix/var/nix/profiles/system-%d-link" % (generation)


def copy_if_not_exists(source, dest):
    if not os.path.exists(dest):
        shutil.copyfile(source, dest)


def get_generations(profile=None):
    gen_list = subprocess.check_output([
        "@nix@/bin/nix-env",
        "--list-generations",
        "-p",
        "/nix/var/nix/profiles/%s" % ("system-profiles/" + profile if profile else "system"),
        "--option", "build-users-group", ""
    ], universal_newlines=True)
    gen_lines = gen_list.split('\n')
    gen_lines.pop()
    return [(profile, int(line.split()[0])) for line in gen_lines]


def get_profiles():
    if os.path.isdir("/nix/var/nix/profiles/system-profiles/"):
        return [
            x for x in os.listdir("/nix/var/nix/profiles/system-profiles/")
            if not x.endswith("-link")
        ]
    return []


def profile_path(profile, generation, name):
    return os.readlink("%s/%s" % (system_dir(profile, generation), name))


def copy_from_profile(profile, generation, name, dry_run=False):
    store_file_path = profile_path(profile, generation, name)
    suffix = os.path.basename(store_file_path)
    store_dir = os.path.basename(os.path.dirname(store_file_path))
    efi_file_path = "/efi/nixos/%s-%s.efi" % (store_dir, suffix)
    if not dry_run:
        copy_if_not_exists(store_file_path, "@efiSysMountPoint@%s" % (efi_file_path))
    return efi_file_path


def describe_generation(generation_dir):
    try:
        with open("%s/nixos-version" % generation_dir) as f:
            nixos_version = f.read()
    except IOError:
        nixos_version = "Unknown"

    kernel_dir = os.path.dirname(os.path.realpath("%s/kernel" % generation_dir))
    module_dir = glob.glob("%s/lib/modules/*" % kernel_dir)[0]
    kernel_version = os.path.basename(module_dir)

    build_time = int(os.path.getctime(generation_dir))
    build_date = datetime.datetime.fromtimestamp(build_time).strftime('%F')

    description = "NixOS {}, Linux Kernel {}, Built on {}".format(
        nixos_version, kernel_version, build_date
    )

    return description


def generation_details(profile, generation):
    kernel = copy_from_profile(profile, generation, "kernel")
    initrd = copy_from_profile(profile, generation, "initrd")
    generation_dir = os.readlink(system_dir(profile, generation))
    kernel_params = "systemConfig=%s init=%s/init " % (generation_dir, generation_dir)
    with open("%s/kernel-params" % (generation_dir)) as params_file:
        kernel_params = kernel_params + params_file.read()
    description = describe_generation(generation_dir)
    return {
        "profile": profile,
        "generation": generation,
        "kernel": kernel,
        "initrd": initrd,
        "kernel_params": kernel_params,
        "description": description
    }


MENU_ENTRY = """
menuentry "NixOS" {{
    loader {kernel}
    initrd {initrd}
    options "{kernel_params}"
    {submenuentries}
}}
"""

SUBMENUENTRY = """
submenuentry "Generation {generation} {description}" {{
    loader {kernel}
    initrd {initrd}
    options "{kernel_params}"
}}
"""


def write_refind_config(path, default_generation, generations):
    with open(path, 'w') as f:
        if "@timeout@" != "":
            f.write("timeout @timeout@")
        f.write(extra_config)

        rev_generations = sorted(generations, key=lambda x: x[1], reverse=True)
        submenuentries = []
        for generation in rev_generations:
            submenuentries.append(SUBMENUENTRY.format(
                **generation_details(*generation)
            ))

        f.write(MENU_ENTRY.format(
            **generation_details(*default_generation),
            submenuentries="\n".join(submenuentries)
        ))


def main():
    parser = argparse.ArgumentParser(description='Update NixOS-related systemd-boot files')
    parser.add_argument('default_config', metavar='DEFAULT-CONFIG', help='The default NixOS config to boot')
    args = parser.parse_args()

    mkdir_p("@efiSysMountPoint@/efi/refind")

    if os.getenv("NIXOS_INSTALL_BOOTLOADER") == "1":

        if "@canTouchEfiVariables@" == "1":
            subprocess.check_call(
                ["@refind@/bin/refind-install"],
                env={"PATH": ":".join([
                    "@efibootmgr@/bin",
                    "@coreutils@/bin",
                    "@utillinux@/bin",
                    "@gnugrep@/bin",
                    "@gnused@/bin",
                    "@gawk@/bin",
                ])}
            )
        else:
            print("DONT KNOW WHAT TO DO")

    if "@extraIcons@" != "":
        icons_dir = "@efiSysMountPoint@/efi/refind/extra-icons"
        if os.path.exists(icons_dir):
            if os.path.exists(icons_dir + "-backup"):
                shutil.rmtree(icons_dir + "-backup")
            os.rename(icons_dir, icons_dir + "-backup")
            print("Notice: Backed up existing extra-icons directory as extra-icons-backup.")
        shutil.copytree("@extraIcons@", icons_dir)

    generations = get_generations()
    for profile in get_profiles():
        generations += get_generations(profile)
    default_generation = None
    for generation in generations:
        if os.readlink(system_dir(*generation)) == args.default_config:
            default_generation = generation

    write_refind_config(
        "@efiSysMountPoint@/efi/refind/refind.conf",
        default_generation,
        generations
    )

    # Since fat32 provides little recovery facilities after a crash,
    # it can leave the system in an unbootable state, when a crash/outage
    # happens shortly after an update. To decrease the likelihood of this
    # event sync the efi filesystem after each update.
    rc = libc.syncfs(os.open("@efiSysMountPoint@", os.O_RDONLY))
    if rc != 0:
        print("could not sync @efiSysMountPoint@: {}".format(os.strerror(rc)), file=sys.stderr)


if __name__ == '__main__':
    main()

refind.nix

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

with lib;

let

  cfg = config.boot.loader.refind;

  efi = config.boot.loader.efi;

  refindBuilder = pkgs.substituteAll {
    src = ./refind-builder.py;

    isExecutable = true;

    inherit (pkgs) python3;

    nix = config.nix.package.out;

    timeout = if config.boot.loader.timeout != null then config.boot.loader.timeout else "";

    extraConfig = cfg.extraConfig;

    extraIcons = if cfg.extraIcons != null then cfg.extraIcons else "";

    inherit (pkgs) refind efibootmgr coreutils gnugrep gnused gawk utillinux;

    inherit (efi) efiSysMountPoint canTouchEfiVariables;
  };

in {

  options.boot.loader.refind = {
    enable = mkOption {
      default = false;
      type = types.bool;
      description = "Whether to enable the refind EFI boot manager";
    };

    extraConfig = mkOption {
      type = types.lines;
      default = "";
      description = "Extra configuration text appended to refind.conf";
    };

    extraIcons = mkOption {
      type = types.nullOr types.path;
      default = null;
      description = "A directory containing icons to be copied to 'extra-icons'";
    };
  };

  config = mkIf cfg.enable {
    assertions = [
      {
        assertion = (config.boot.kernelPackages.kernel.features or { efiBootStub = true; }) ? efiBootStub;

        message = "This kernel does not support the EFI boot stub";
      }
    ];

    boot.loader.grub.enable = mkDefault false;

    boot.loader.supportsInitrdSecrets = false; # TODO what does this do ?

    system = {
      build.installBootLoader = refindBuilder;

      boot.loader.id = "refind";

      requiredKernelConfig = with config.lib.kernelConfig; [
        (isYes "EFI_STUB")
      ];
    };
  };

}

Hey @betaboon! Thanks so much for open-sourcing this script. I'm new to NixOS, and I was looking into using rEFInd as my bootloader, and was thinking along the lines of generating menuentries programatically for NixOS generations, and it looks like these scripts do exactly that. Is it sufficient to just import the .nix file in my configuration.nix and add the right configs? Also, have you used this script recently / do you know if it's still working with 20.04?

Thanks again!

EDIT: Decided to dive in, and it works on 20.04! Thanks so much! For people in the future: you will most likely need to mess with efibootmgr to add rEFInd and/or take out other bootloaders.

Thanks again!

+1! Still works in 2024!