anchor.diff:          default = true;
           description =
             ''
  -            Whether to run qemu with a graphics window, or access
  +            Whether to run QEMU with a graphics window, or access
               the guest computer serial port through the host tty.
             '';
         };
   
  +    virtualisation.pathsInNixDB =
  +      mkOption {
  +        default = [];
  +        description =
  +          ''
  +            The list of paths whose closure is registered in the Nix
  +            database in the VM.  All other paths in the host Nix store
  +            appear in the guest Nix store as well, but are considered
  +            garbage (because they are not registered in the Nix
  +            database in the guest).
  +          '';
  +      };
  +      
     };
   
     cfg = config.virtualisation;
  
positive.code:       fi
      '';
  
    # Mount the host filesystem via CIFS, and bind-mount the Nix store
    # of the host into our own filesystem.  We use mkOverride to allow
    # this module to be applied to "normal" NixOS system configuration,
  
negative.code:         options = "bind";
          neededForBoot = true;
        }
      ];
  
    # Starting DHCP brings down eth0, which kills the connection to the
  