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:       };
      };
    };
    config = mkIf cfg.enable 
    {
      jobs.gvpe = {
        description = "GNU Virtual Private Ethernet node";
        
  
negative.code:         chown root /var/gvpe
          chmod 700 /var/gvpe
          cp ${finalConfig} /var/gvpe/gvpe.conf
          cp ${ifupScript} /var/gvpe/if-up
        '';
  
        inherit exec;
  