anchor.diff:  
     config = mkIf cfg.enable {
   
  -    environment.systemPackages = [ pkgs.xen ];
  +    environment.systemPackages = [ xen ];
   
       # Domain 0 requires a pvops-enabled kernel.
       boot.kernelPackages = pkgs.linuxPackages_2_6_32_xen;
   
  -    boot.kernelModules = [ "xen_evtchn" "xen_gntdev" ];
  +    boot.kernelModules = [ "xen_evtchn" "xen_gntdev" "xen_blkback" "xen_netback" "xen_pciback" "blktap" ];
   
       # The radeonfb kernel module causes the screen to go black as soon
       # as it's loaded, so don't load it.
  
positive.code:     # virtual device), start dhclient after xend.
      jobs.dhclient.startOn = mkOverride 50 "started xend";
  
    };
  
  }
  
negative.code: 
          path = 
            [ pkgs.bridge_utils pkgs.gawk pkgs.iproute pkgs.nettools 
              pkgs.utillinux pkgs.bash xen pkgs.pciutils pkgs.procps
            ];
  
          preStart = "${xen}/sbin/xend start";
  
          postStop = "${xen}/sbin/xend stop";
        };
  
      # To prevent a race between dhclient and xend's bridge setup
  