anchor.diff:        };
       };
   
  -    swapDevices = mkVMOverride [ ];
  -    boot.initrd.luks.devices = mkVMOverride {};
  +    swapDevices = (if cfg.useDefaultFilesystems then mkVMOverride else mkDefault) [ ];
  +    boot.initrd.luks.devices = (if cfg.useDefaultFilesystems then mkVMOverride else mkDefault) {};
   
       # Don't run ntpd in the guest.  It should get the correct time from KVM.
       services.timesyncd.enable = false;
  
positive.code:           '';
        };
  
      virtualisation.efiVars =
        mkOption {
          type = types.str;
  
negative.code:         };
      in
        mkVMOverride (cfg.fileSystems //
        optionalAttrs cfg.useDefaultFilesystems {
          "/".device = cfg.bootDevice;
          "/".fsType = "ext4";
          "/".autoFormat = true;
        } //
        optionalAttrs config.boot.tmpOnTmpfs {
          "/tmp" = {
            device = "tmpfs";
            fsType = "tmpfs";
            neededForBoot = true;
            # Sync with systemd's tmp.mount;
            options = [ "mode=1777" "strictatime" "nosuid" "nodev" "size=${toString config.boot.tmpOnTmpfsSize}" ];
          };
        } //
        optionalAttrs cfg.useNixStoreImage {
          "/nix/${if cfg.writableStore then ".ro-store" else "store"}" = {
            device = "${lookupDriveDeviceName "nix-store" cfg.qemu.drives}";
            neededForBoot = true;
            options = [ "ro" ];
          };
        } //
        optionalAttrs (cfg.writableStore && cfg.writableStoreUseTmpfs) {
          "/nix/.rw-store" = {
            fsType = "tmpfs";
            options = [ "mode=0755" ];
            neededForBoot = true;
          };
        } //
        optionalAttrs cfg.useBootLoader {
          # see note [Disk layout with `useBootLoader`]
          "/boot" = {
            device = "${lookupDriveDeviceName "boot" cfg.qemu.drives}2"; # 2 for e.g. `vdb2`, as created in `bootDisk`
            fsType = "vfat";
            noCheck = true; # fsck fails on a r/o filesystem
          };
        } // lib.mapAttrs' mkSharedDir cfg.sharedDirectories);
  
      boot.initrd.systemd = lib.mkIf (config.boot.initrd.systemd.enable && cfg.writableStore) {
  