anchor.diff:  
       virtualisation.libvirtd.enableKVM =
         mkOption {
  +        type = types.bool;
           default = true;
           description =
             ''
  
positive.code: 
      virtualisation.libvirtd.enable =
        mkOption {
          default = false;
          description =
            ''
  
negative.code: 
      virtualisation.libvirtd.extraConfig =
        mkOption {
          type = types.lines;
          default = "";
          description =
            ''
  