dotfiles/example/microvm/system.nix

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

{
  config = lib.mkIf config.microvm.guest.enable {
    assertions = [
      {
        assertion =
          (config.microvm.writableStoreOverlay != null)
          -> (!config.nix.optimise.automatic && !config.nix.settings.auto-optimise-store);
        message = ''
          `nix.optimise.automatic` and `nix.settings.auto-optimise-store` do not work with `microvm.writableStoreOverlay`.
        '';
      }
    ];

    boot.loader.grub.enable = false;
    # boot.initrd.systemd.enable = lib.mkDefault true;
    boot.initrd.kernelModules = [
      "virtio_mmio"
      "virtio_pci"
      "virtio_blk"
      "9pnet_virtio"
      "9p"
      "virtiofs"
    ]
    ++
      lib.optionals
        (pkgs.stdenv.targetPlatform.system == "x86_64-linux" && config.microvm.hypervisor == "firecracker")
        [
          # Keyboard controller that can receive CtrlAltDel
          "i8042"
        ]
    ++ lib.optionals (config.microvm.writableStoreOverlay != null) [
      "overlay"
    ];

    microvm.kernelParams =
      let
        # When a store disk is used, we can drop references to the packed contents as the squashfs/erofs contains all paths.
        toplevel =
          if config.microvm.storeOnDisk then
            builtins.unsafeDiscardStringContext config.system.build.toplevel
          else
            config.system.build.toplevel;
      in
      config.boot.kernelParams
      ++ [
        "init=${toplevel}/init"
      ];

    # modules that consume boot time but have rare use-cases
    boot.blacklistedKernelModules = [
      "rfkill"
      "intel_pstate"
    ]
    ++ lib.optional (!config.microvm.graphics.enable) "drm";

    systemd =
      let
        # nix-daemon works only with a writable /nix/store
        enableNixDaemon = config.microvm.writableStoreOverlay != null;
      in
      {
        services.nix-daemon.enable = lib.mkDefault enableNixDaemon;
        sockets.nix-daemon.enable = lib.mkDefault enableNixDaemon;

        # consumes a lot of boot time
        services.mount-pstore.enable = false;

        # just fails in the usual usage of microvm.nix
        generators = {
          systemd-gpt-auto-generator = "/dev/null";
        };
      };

  };
}