anchor.diff:  let
   
     cfg = config.libvirt.test;
  +
  +  ztail = pkgs.haskell.packages.ghc784.callPackage (
  +    { mkDerivation, array, base, containers, filepath, hinotify
  +    , old-locale, process, regex-compat, stdenv, time, unix
  +    }:
  +    mkDerivation {
  +      pname = "ztail";
  +      version = "1.1";
  +      sha256 = "11x6whwyfgdgda5bhdck0k12inzix8cjfm42hh09p703nalk07nq";
  +      isLibrary = false;
  +      isExecutable = true;
  +      executableHaskellDepends = [
  +        array base containers filepath hinotify old-locale process
  +        regex-compat time unix
  +      ];
  +      description = "Multi-file, colored, filtered log tailer";
  +      license = stdenv.lib.licenses.bsd3;
  +    }
  +  ) {};
   
     inherit (import ../lib.nix) hexByteToInt mkMAC;
   
  
positive.code:         # Variables that are substituted within the libvirt XML files
          testid="$(basename "$out")"
          testid="''${testid%%-*}"
          pwd="$(pwd)"
          uid="$(id -u)"
          gid="$(id -g)"
  
          # Setup directories and libvirt XML files
          mkdir -p out/libvirt out/hosts/{${instList}}
          touch out/hosts/{${instList}}/{console,journal}.log
          cp -t out/libvirt "$src"/*
          for f in out/libvirt/{dom,net}-*.xml; do substituteAllInPlace "$f"; done
          ${optionalString (cfg.backend == "lxc") "mkdir root-{${instList}}"}
  
          # Let libvirt access paths inside the build directory and write to out dir
          chmod a+x .
          chmod a+w out/hosts/*
  
          tail -Fq out/hosts/test-driver/script.std{out,err} \
            out/hosts/{${instList}}/{console,journal}.log 2>/dev/null &
  
          ${pkgs.libvirt}/bin/virsh -c "${cfg.connectionURI}" \
            "${virshCmds}" >/dev/null || exit 1
  
          cleanup
        '';
  
        installPhase = "mv out $out";
      };
  
    };
  
negative.code:       };
  
        test-driver = {
          hostName = mkOption {
            type = types.str;
            default = "driver";
          };
  
          script = mkOption {
            type = types.path;
            description = ''
  