nixos: Support systemd-gpt-auto-root

nixos/modules/system/boot/stage-1.nix

@@ -688,7 +688,7 @@ in
 
   config = mkIf config.boot.initrd.enable {
     assertions = [
-      { assertion = any (fs: fs.mountPoint == "/") fileSystems;
+      { assertion = !config.boot.initrd.systemd.enable -> any (fs: fs.mountPoint == "/") fileSystems;
         message = "The ‘fileSystems’ option does not specify your root file system.";
       }
       { assertion = let inherit (config.boot) resumeDevice; in

nixos/modules/system/boot/systemd/initrd.nix

@@ -212,6 +212,19 @@ in {
       default = [];
     };
 
+    root = lib.mkOption {
+      type = lib.types.enum [ "fstab" "gpt-auto" ];
+      default = "fstab";
+      example = "gpt-auto";
+      description = ''
+        Controls how systemd will interpret the root FS in initrd. See
+        {manpage}`kernel-command-line(7)`. NixOS currently does not
+        allow specifying the root file system itself this
+        way. Instead, the `fstab` value is used in order to interpret
+        the root file system specified with the `fileSystems` option.
+      '';
+    };
+
     emergencyAccess = mkOption {
       type = with types; oneOf [ bool (nullOr (passwdEntry str)) ];
       description = lib.mdDoc ''
@@ -342,7 +355,12 @@ in {
   };
 
   config = mkIf (config.boot.initrd.enable && cfg.enable) {
-    assertions = map (name: {
+    assertions = [
+      {
+        assertion = cfg.root == "fstab" -> any (fs: fs.mountPoint == "/") (builtins.attrValues config.fileSystems);
+        message = "The ‘fileSystems’ option does not specify your root file system.";
+      }
+    ] ++ map (name: {
       assertion = lib.attrByPath name (throw "impossible") config.boot.initrd == "";
       message = ''
         systemd stage 1 does not support 'boot.initrd.${lib.concatStringsSep "." name}'. Please
@@ -371,7 +389,12 @@ in {
       "autofs"
       # systemd-cryptenroll
     ] ++ lib.optional cfg.enableTpm2 "tpm-tis"
-    ++ lib.optional (cfg.enableTpm2 && !(pkgs.stdenv.hostPlatform.isRiscV64 || pkgs.stdenv.hostPlatform.isArmv7)) "tpm-crb";
+    ++ lib.optional (cfg.enableTpm2 && !(pkgs.stdenv.hostPlatform.isRiscV64 || pkgs.stdenv.hostPlatform.isArmv7)) "tpm-crb"
+    ++ lib.optional cfg.package.withEfi "efivarfs";
+
+    boot.kernelParams = [
+      "root=${config.boot.initrd.systemd.root}"
+    ] ++ lib.optional (config.boot.resumeDevice != "") "resume=${config.boot.resumeDevice}";
 
     boot.initrd.systemd = {
       initrdBin = [pkgs.bash pkgs.coreutils cfg.package.kmod cfg.package];
@@ -554,7 +577,5 @@ in {
         serviceConfig.Type = "oneshot";
       };
     };
-
-    boot.kernelParams = lib.mkIf (config.boot.resumeDevice != "") [ "resume=${config.boot.resumeDevice}" ];
   };
 }

nixos/tests/installer-systemd-stage-1.nix

@@ -37,6 +37,7 @@
     clevisLuksFallback
     clevisZfs
     clevisZfsFallback
+    gptAutoRoot
     ;
 
 }

nixos/tests/installer.nix

@@ -82,6 +82,7 @@ let
   testScriptFun = { bootLoader, createPartitions, grubDevice, grubUseEfi, grubIdentifier
                   , postInstallCommands, preBootCommands, postBootCommands, extraConfig
                   , testSpecialisationConfig, testFlakeSwitch, clevisTest, clevisFallbackTest
+                  , disableFileSystems
                   }:
     let
       qemu-common = import ../lib/qemu-common.nix { inherit (pkgs) lib pkgs; };
@@ -163,7 +164,7 @@ let
       ${createPartitions}
 
       with subtest("Create the NixOS configuration"):
-          machine.succeed("nixos-generate-config --root /mnt")
+          machine.succeed("nixos-generate-config ${optionalString disableFileSystems "--no-filesystems"} --root /mnt")
           machine.succeed("cat /mnt/etc/nixos/hardware-configuration.nix >&2")
           machine.copy_from_host(
               "${ makeConfig {
@@ -433,6 +434,7 @@ let
     , testFlakeSwitch ? false
     , clevisTest ? false
     , clevisFallbackTest ? false
+    , disableFileSystems ? false
     }:
     makeTest {
       inherit enableOCR;
@@ -541,7 +543,8 @@ let
       testScript = testScriptFun {
         inherit bootLoader createPartitions postInstallCommands preBootCommands postBootCommands
                 grubDevice grubIdentifier grubUseEfi extraConfig
-                testSpecialisationConfig testFlakeSwitch clevisTest clevisFallbackTest;
+                testSpecialisationConfig testFlakeSwitch clevisTest clevisFallbackTest
+                disableFileSystems;
       };
     };
 
@@ -1414,4 +1417,39 @@ in {
       };
     };
   };
+
+  gptAutoRoot = let
+    rootPartType = {
+      ia32 = "44479540-F297-41B2-9AF7-D131D5F0458A";
+      x64 = "4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709";
+      arm = "69DAD710-2CE4-4E3C-B16C-21A1D49ABED3";
+      aa64 = "B921B045-1DF0-41C3-AF44-4C6F280D3FAE";
+    }.${pkgs.stdenv.hostPlatform.efiArch};
+  in makeInstallerTest "gptAutoRoot" {
+    disableFileSystems = true;
+    createPartitions = ''
+      machine.succeed(
+        "sgdisk --zap-all /dev/vda",
+        "sgdisk --new=1:0:+100M --typecode=0:ef00 /dev/vda", # /boot
+        "sgdisk --new=2:0:+1G --typecode=0:8200 /dev/vda", # swap
+        "sgdisk --new=3:0:+5G --typecode=0:${rootPartType} /dev/vda", # /
+        "udevadm settle",
+
+        "mkfs.vfat /dev/vda1",
+        "mkswap /dev/vda2 -L swap",
+        "swapon -L swap",
+        "mkfs.ext4 -L root /dev/vda3",
+        "udevadm settle",
+
+        "mount /dev/vda3 /mnt",
+        "mkdir -p /mnt/boot",
+        "mount /dev/vda1 /mnt/boot"
+      )
+    '';
+    bootLoader = "systemd-boot";
+    extraConfig = ''
+      boot.initrd.systemd.root = "gpt-auto";
+      boot.initrd.supportedFilesystems = ["ext4"];
+    '';
+  };
 }

pkgs/os-specific/linux/systemd/default.nix

@@ -866,7 +866,7 @@ stdenv.mkDerivation (finalAttrs: {
     # needed - and therefore `interfaceVersion` should be incremented.
     interfaceVersion = 2;
 
-    inherit withBootloader withCryptsetup withHostnamed withImportd withKmod
+    inherit withBootloader withCryptsetup withEfi withHostnamed withImportd withKmod
       withLocaled withMachined withPortabled withTimedated withUtmp util-linux kmod kbd;
 
     tests = {