anchor.diff:    # 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=none,noperm,noacl";
  +          options = "guest,sec=${mode},noperm,noacl";
           };
         "/tmp/xchg" =
           { device = "//10.0.2.4/xchg";
             fsType = "cifs";
  -          options = "guest,sec=none,noperm,noacl";
  +          options = "guest,sec=${mode},noperm,noacl";
             neededForBoot = true;
           };
         "/tmp/shared" =
           { device = "//10.0.2.4/shared";
             fsType = "cifs";
  -          options = "guest,sec=none,noperm,noacl";
  +          options = "guest,sec=${mode},noperm,noacl";
             neededForBoot = true;
           };
       } // optionalAttrs cfg.useBootLoader
  
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:           options = "ro";
            noCheck = true; # fsck fails on a r/o filesystem
          };
      });
  
    swapDevices = mkOverride 50 [ ];
  
  