nixos/qemu-firmware: init

Link QEMU firmware descriptors to /etc/qemu/firmware, where
systemd-vmspawn and other tools discover firmware for running VMs.

Signed-off-by: Paul Meyer <katexochen0@gmail.com>

nixos/doc/manual/release-notes/rl-2611.section.md

@@ -128,6 +128,8 @@
 
 - `security.run0.persistentAuth` options have been added to support persistent Authentication of session. Timeout configurable via `security.polkit.settings.Polkitd.ExpirationSeconds`.
 
+- [`virtualisation.qemu.firmware.enable`](#opt-virtualisation.qemu.firmware.enable) has been added to install QEMU firmware descriptors to {file}`/etc/qemu/firmware`, making the corresponding firmware images discoverable by tools such as `systemd-vmspawn`. By default this exposes the firmware bundled with QEMU. Further firmware can be added via [`virtualisation.qemu.firmware.packages`](#opt-virtualisation.qemu.firmware.packages), for example the new `OVMF-amdsev` and `OVMF-inteltdx` packages, which provide UEFI firmware for AMD SEV-SNP and Intel TDX confidential VMs.
+
 - `boot.loader.systemd-boot` gained support for [Automatic Boot Assessment](https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT/) via the new [`boot.loader.systemd-boot.bootCounting`](#opt-boot.loader.systemd-boot.bootCounting.enable) options, allowing automatic detection of and recovery from bad NixOS generations. As part of this change, boot loader entries on the ESP/XBOOTLDR partition are now named `nixos-<content-hash>.conf` instead of `nixos-generation-<n>.conf`; existing entries are migrated automatically on the next `nixos-rebuild boot`/`switch`.
 
 - `services.nginx` gained a [`lua`](#opt-services.nginx.lua.enable) option to enable Lua scripting via OpenResty's lua-nginx-module on a stock nginx, configuring `lua_package_path`/`lua_package_cpath` from the packages listed in [`services.nginx.lua.extraPackages`](#opt-services.nginx.lua.extraPackages). Use this to add Lua to a regular nginx; for the full OpenResty platform (libraries that rely on its bundled lualib, such as `lua-resty-openidc`), set `services.nginx.package` to `pkgs.openresty` instead — the option configures the Lua search path for it too.

nixos/modules/module-list.nix

@@ -2052,6 +2052,7 @@
   ./virtualisation/openvswitch.nix
   ./virtualisation/parallels-guest.nix
   ./virtualisation/podman/default.nix
+  ./virtualisation/qemu-firmware.nix
   ./virtualisation/qemu-guest-agent.nix
   ./virtualisation/rosetta.nix
   ./virtualisation/spice-usb-redirection.nix

nixos/modules/tasks/filesystems/envfs.nix

@@ -69,7 +69,7 @@ in
   config = lib.mkIf (cfg.enable) {
     environment.systemPackages = [ cfg.package ];
     # we also want these mounts in virtual machines.
-    fileSystems = if config.virtualisation ? qemu then lib.mkVMOverride mounts else mounts;
+    fileSystems = if config.virtualisation.qemu ? package then lib.mkVMOverride mounts else mounts;
 
     # We no longer need those when using envfs
     system.activationScripts.usrbinenv = lib.mkForce "";

nixos/modules/testing/test-instrumentation.nix

@@ -196,7 +196,7 @@ in
     # that do not specify any nodes, or an empty attr set as nodes) will not
     # have the QEMU module loaded and thuse these options can't and should not
     # be set.
-    virtualisation = lib.optionalAttrs (options ? virtualisation.qemu) {
+    virtualisation = lib.optionalAttrs (options ? virtualisation.qemu.package) {
       qemu = {
         # NOTE: optionalAttrs
         #       test-instrumentation.nix appears to be used without qemu-vm.nix, so

nixos/modules/virtualisation/qemu-firmware.nix

@@ -0,0 +1,50 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.virtualisation.qemu.firmware;
+in
+
+{
+  options.virtualisation.qemu.firmware = {
+    enable = lib.mkEnableOption "QEMU firmware descriptors in {file}`/etc/qemu/firmware`";
+
+    packages = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ pkgs.qemu ];
+      defaultText = lib.literalExpression "[ pkgs.qemu ]";
+      example = lib.literalExpression "[ pkgs.qemu pkgs.OVMF-amdsev.fd ]";
+      description = ''
+        Packages providing QEMU firmware descriptors under
+        {file}`share/qemu/firmware`, following the QEMU firmware interop
+        convention (see {file}`docs/interop/firmware.json` in the QEMU
+        source tree). The descriptors are merged and linked to
+        {file}`/etc/qemu/firmware`, where tools like
+        {command}`systemd-vmspawn` discover the firmware available for
+        running virtual machines.
+
+        The default exposes the descriptors of the firmware images
+        bundled with QEMU. Note that setting this option replaces the
+        default, so include `pkgs.qemu` when adding further firmware.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.etc."qemu/firmware".source =
+      let
+        merged = pkgs.buildEnv {
+          name = "qemu-firmware-descriptors";
+          paths = cfg.packages;
+          pathsToLink = [ "/share/qemu/firmware" ];
+        };
+      in
+      "${merged}/share/qemu/firmware";
+  };
+
+  meta.maintainers = [ lib.maintainers.katexochen ];
+}

nixos/tests/all-tests.nix

@@ -1442,6 +1442,7 @@ in
   pykms = runTest ./pykms.nix;
   qbittorrent = runTest ./qbittorrent.nix;
   qboot = runTestOn [ "x86_64-linux" "i686-linux" ] ./qboot.nix;
+  qemu-firmware = runTestOn [ "x86_64-linux" ] ./qemu-firmware.nix;
   qemu-vm-external-disk-image = runTest ./qemu-vm-external-disk-image.nix;
   qemu-vm-restrictnetwork = handleTest ./qemu-vm-restrictnetwork.nix { };
   qemu-vm-store = runTest ./qemu-vm-store.nix;

nixos/tests/qemu-firmware.nix

@@ -0,0 +1,41 @@
+{ lib, ... }:
+
+{
+  name = "qemu-firmware";
+  meta.maintainers = [ lib.maintainers.katexochen ];
+
+  nodes.machine =
+    { pkgs, ... }:
+    {
+      virtualisation.qemu.firmware = {
+        enable = true;
+        packages = [
+          pkgs.qemu
+          pkgs.OVMF-amdsev.fd
+          pkgs.OVMF-inteltdx.fd
+        ];
+      };
+      environment.systemPackages = [ pkgs.jq ];
+    };
+
+  testScript = ''
+    machine.wait_for_unit("multi-user.target")
+
+    with subtest("descriptors are merged into /etc/qemu/firmware"):
+        machine.succeed("test -e /etc/qemu/firmware/60-edk2-x86_64.json")
+        machine.succeed("test -e /etc/qemu/firmware/61-edk2-ovmf-x64-amdsev.json")
+        machine.succeed("test -e /etc/qemu/firmware/61-edk2-ovmf-x64-inteltdx.json")
+
+    with subtest("descriptors reference existing firmware images"):
+        machine.succeed(
+            "jq -er '.mapping | .filename // .executable.filename' "
+            + "/etc/qemu/firmware/*.json | xargs stat --"
+        )
+
+    with subtest("systemd-vmspawn discovers the descriptors"):
+        listed = machine.succeed("systemd-vmspawn --firmware=list")
+        assert "61-edk2-ovmf-x64-amdsev.json" in listed
+        assert "61-edk2-ovmf-x64-inteltdx.json" in listed
+        assert "60-edk2-x86_64.json" in listed
+  '';
+}