anchor.diff:            options = "ro";
             noCheck = true; # fsck fails on a r/o filesystem
           };
  -    };
  +    });
   
     swapDevices = mkOverride 50 [ ];
   
  
positive.code:   # CIFS.  Also use paravirtualised network and block devices for
    # performance.
    boot.initrd.availableKernelModules =
      [ "cifs" "nls_utf8" "hmac" "md4" "ecb" "des_generic" ];
  
    boot.initrd.supportedFilesystems = optional cfg.writableStore "unionfs-fuse";
  
  
negative.code:   # disregarded for the purpose of building a VM test image (since
    # those filesystems don't exist in the VM).
    fileSystems = mkOverride 10
      (let mode = if builtins.compareVersions "3.5" config.boot.kernelPackages.kernel.version == 1 then "none" else "ntlm"; in
      { "/".device = "/dev/vda";
        "/nix/store" =
          { device = "//10.0.2.4/store";
            fsType = "cifs";
            options = "guest,sec=${mode},noperm,noacl";
          };
        "/tmp/xchg" =
          { device = "//10.0.2.4/xchg";
            fsType = "cifs";
            options = "guest,sec=${mode},noperm,noacl";
            neededForBoot = true;
          };
        "/tmp/shared" =
          { device = "//10.0.2.4/shared";
            fsType = "cifs";
            options = "guest,sec=${mode},noperm,noacl";
            neededForBoot = true;
          };
      } // optionalAttrs cfg.useBootLoader
  