anchor.diff:    services.mingetty.ttys = ttys ++ optional (!cfg.graphics) "ttyS0";
   
     # Wireless won't work in the VM.
  -  networking.enableWLAN = mkOverrideTemplate 50 {} false;
  +  networking.enableWLAN = mkOverride 50 false;
   }
  
positive.code:   virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
    
    # Mount the host filesystem via CIFS, and bind-mount the Nix store
    # of the host into our own filesystem.  We use mkOverrideTemplate to allow
    # this module to be applied to "normal" NixOS system configuration,
    # where the regular value for the `fileSystems' attribute should be
    # disregarded for the purpose of building a VM test image (since
    # those filesystems don't exist in the VM).
    fileSystems = mkOverrideTemplate 50 {}
      [ { mountPoint = "/";
          device = "/dev/vda";
        }
  
negative.code:   # host filesystem and thus deadlocks the system.
    networking.useDHCP = false;
  
    networking.defaultGateway = mkOverride 200 "10.0.2.2";
  
    networking.nameservers = [ "10.0.2.3" ];
  
  