anchor.diff:  
   let 
     inherit (pkgs.lib) mkOption mkIf;
  +
     cfg = config.services.gvpe;
  +
     finalConfig = if cfg.configFile != null then 
       cfg.configFile
     else if cfg.configText != null then
  
positive.code:     '';
      executable = true;
    });
    exec = "${pkgs.gvpe}/sbin/gvpe -c /var/gvpe -D ${cfg.nodename} "
      + " ${cfg.nodename}.pid-file=/var/gvpe/gvpe.pid"
      + " ${cfg.nodename}.if-up=if-up"
      + " &> /var/log/gvpe";
    inherit (cfg) startOn stopOn;
  in
  
  
negative.code:         chown root /var/gvpe
          chmod 700 /var/gvpe
          cp ${finalConfig} /var/gvpe/gvpe.conf
          cp ${ifupScript} /var/gvpe/if-up
        '';
  
        inherit exec;
  