anchor.diff:    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
  +  # of the host into our own filesystem.  We use mkOverride 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 {}
  +  fileSystems = mkOverride 50
       [ { mountPoint = "/";
           device = "/dev/vda";
         }
  
positive.code:   services.mingetty.ttys = ttys ++ optional (!cfg.graphics) "ttyS0";
  
    # Wireless won't work in the VM.
    networking.enableWLAN = mkOverrideTemplate 50 {} false;
  }
  
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" ];
  
  