anchor.diff:  
       system.extraSystemBuilderCmds =
         ''
  -        ln -s ${pkgs.xen}/boot/xen.gz $out/xen.gz
  +        ln -s ${xen}/boot/xen.gz $out/xen.gz
           echo "${toString cfg.bootParams}" > $out/xen-params
         '';
   
  
positive.code: 
    config = mkIf cfg.enable {
  
      environment.systemPackages = [ pkgs.xen ];
  
      # Domain 0 requires a pvops-enabled kernel.
      boot.kernelPackages = pkgs.linuxPackages_2_6_32_xen;
  
      boot.kernelModules = [ "xen_evtchn" "xen_gntdev" ];
  
      # The radeonfb kernel module causes the screen to go black as soon
      # as it's loaded, so don't load it.
  
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
  