nixos/boot/external: init

This allows supporting external bootloader backends.

3 files changed, 105 insertions, 0 deletions

diff --git a/nixos/modules/system/boot/loader/external/external.md b/nixos/modules/system/boot/loader/external/external.md
new file mode 100644
index 0000000000000..a53ab55baf5b3
--- /dev/null
+++ b/nixos/modules/system/boot/loader/external/external.md
@@ -0,0 +1,26 @@
+# External Bootloader Backends {#sec-bootloader-external}
+
+NixOS has support for several bootloader backends by default: systemd-boot, grub, uboot, etc.
+The built-in bootloader backend support is generic and supports most use cases.
+Some users may prefer to create advanced workflows around managing the bootloader and bootable entries.
+
+You can replace the built-in bootloader support with your own tooling using the "external" bootloader option.
+
+Imagine you have created a new packaged called FooBoot.
+FooBoot provides a program at `${pkgs.fooboot}/bin/fooboot-install` which takes the system closure's path as its only argument and configures the system's bootloader.
+
+You can enable FooBoot like this:
+
+```nix
+{ pkgs, ... }: {
+  boot.loader.external = {
+    enable = true;
+    installHook = "${pkgs.fooboot}/bin/fooboot-install";
+  };
+}
+```
+
+## Developing Custom Bootloader Backends
+
+Bootloaders should use [RFC-0125](https://github.com/NixOS/rfcs/pull/125)'s Bootspec format and synthesis tools to identify the key properties for bootable system generations.
+
diff --git a/nixos/modules/system/boot/loader/external/external.nix b/nixos/modules/system/boot/loader/external/external.nix
new file mode 100644
index 0000000000000..86f4eaaeba468
--- /dev/null
+++ b/nixos/modules/system/boot/loader/external/external.nix
@@ -0,0 +1,38 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.boot.loader.external;
+in
+{
+  meta = {
+    maintainers = with maintainers; [ cole-h grahamc ];
+    # Don't edit the docbook xml directly, edit the md and generate it:
+    # `pandoc external.md -t docbook --top-level-division=chapter --extract-media=media -f markdown+smart > external.xml`
+    doc = ./external.xml;
+  };
+
+  options.boot.loader.external = {
+    enable = mkEnableOption "use an external tool to install your bootloader";
+
+    installHook = mkOption {
+      type = with types; path;
+      description = ''
+        The full path to a program of your choosing which performs the bootloader installation process.
+
+        The program will be called with an argument pointing to the output of the system's toplevel.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    boot.loader = {
+      grub.enable = mkDefault false;
+      systemd-boot.enable = mkDefault false;
+      supportsInitrdSecrets = false;
+    };
+
+    system.build.installBootLoader = cfg.installHook;
+  };
+}
diff --git a/nixos/modules/system/boot/loader/external/external.xml b/nixos/modules/system/boot/loader/external/external.xml
new file mode 100644
index 0000000000000..b024e7dd4031d
--- /dev/null
+++ b/nixos/modules/system/boot/loader/external/external.xml
@@ -0,0 +1,41 @@
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-bootloader-external">
+  <title>External Bootloader Backends</title>
+  <para>
+    NixOS has support for several bootloader backends by default:
+    systemd-boot, grub, uboot, etc. The built-in bootloader backend
+    support is generic and supports most use cases. Some users may
+    prefer to create advanced workflows around managing the bootloader
+    and bootable entries.
+  </para>
+  <para>
+    You can replace the built-in bootloader support with your own
+    tooling using the <quote>external</quote> bootloader option.
+  </para>
+  <para>
+    Imagine you have created a new packaged called FooBoot. FooBoot
+    provides a program at
+    <literal>${pkgs.fooboot}/bin/fooboot-install</literal> which takes
+    the system closure’s path as its only argument and configures the
+    system’s bootloader.
+  </para>
+  <para>
+    You can enable FooBoot like this:
+  </para>
+  <programlisting language="bash">
+{ pkgs, ... }: {
+  boot.loader.external = {
+    enable = true;
+    installHook = &quot;${pkgs.fooboot}/bin/fooboot-install&quot;;
+  };
+}
+</programlisting>
+  <section xml:id="developing-custom-bootloader-backends">
+    <title>Developing Custom Bootloader Backends</title>
+    <para>
+      Bootloaders should use
+      <link xlink:href="https://github.com/NixOS/rfcs/pull/125">RFC-0125</link>’s
+      Bootspec format and synthesis tools to identify the key properties
+      for bootable system generations.
+    </para>
+  </section>
+</chapter>