anchor.diff:      mkdir -p $out/{servers,ip}
   
       ${concatMapStrings (ip: ''
  -      echo > "$out/ip/"${lib.escapeShellArg ip}
  +      touch "$out/ip/"${lib.escapeShellArg ip}
       '') cfg.clientIps}
   
       ${concatStrings (mapAttrsToList (host: ips: ''
  
positive.code:       '';
        script = ''
          cd /var/lib/dnscache/
          exec ./run
        '';
      };
  
negative.code: 
    options = {
      services.dnscache = {
  
        enable = mkOption {
          default = false;
          type = types.bool;
          description = "Whether to run the dnscache caching dns server.";
        };
  
        ip = mkOption {
          default = "0.0.0.0";
          type = types.str;
          description = "IP address on which to listen for connections.";
        };
  
        clientIps = mkOption {
          default = [ "127.0.0.1" ];
          type = types.listOf types.str;
          description = "Client IP addresses (or prefixes) from which to accept connections.";
          example = ["192.168" "172.23.75.82"];
        };
  
        domainServers = mkOption {
          default = { };
          type = types.attrsOf (types.listOf types.str);
          description = ''
            Table of {hostname: server} pairs to use as authoritative servers for hosts (and subhosts).
            If entry for @ is not specified predefined list of root servers is used.
          '';
          example = {
            "@" = ["8.8.8.8" "8.8.4.4"];
            "example.com" = ["192.168.100.100"];
          };
        };
  
        forwardOnly = mkOption {
          default = false;
          type = types.bool;
          description = ''
            Whether to treat root servers (for @) as caching
            servers, requesting addresses the same way a client does. This is
            needed if you want to use e.g. Google DNS as your upstream DNS.
          '';
        };
  
      };
    };
  
  