anchor.diff:    config = mkIf config.sound.enable {
   
       environment.systemPackages = [ alsaUtils ];
  +
  +    environment.etc = [ { source = config.sound.extraConfig;
  +                          target = configPath;
  +                        }
  +                      ];
   
       # ALSA provides a udev rule for restoring volume settings.
       services.udev.packages = [ alsaUtils ];
  
positive.code:   inherit (pkgs) alsaUtils;
  
    soundState = "/var/lib/alsa/asound.state";
  
  in
  
  
negative.code:         '';
        };
  
        extraConfig = mkOption {
          type = types.lines;
          default = '''';
          example = ''
            defaults.pcm.!card 3
          '';
          description = ''
            Set addition configuration for system-wide alsa.
          '';
        };
  
      };
  
    };
  