anchor.diff:  
     preConfigure =
       ''
  +      substituteInPlace configure --replace "/usr/bin/file" "${file}/bin/file"
         sed -i "includes/dhcpd.h" \
   	-"es|^ *#define \+_PATH_DHCLIENT_SCRIPT.*$|#define _PATH_DHCLIENT_SCRIPT \"$out/sbin/dhclient-script\"|g"
       '';
  
positive.code: { stdenv, fetchurl, nettools, iputils, iproute, makeWrapper, coreutils, gnused }:
  
  stdenv.mkDerivation rec {
    name = "dhcp-4.1-ESV-R6";
    
    src = fetchurl {
      url = http://ftp.isc.org/isc/dhcp/4.1-ESV-R6/dhcp-4.1-ESV-R6.tar.gz;
      sha256 = "17md1vml07szl9dx4875gfg4sgnb3z73glpbq1si7p82mfhnddny";
    };
  
    patches =
  
negative.code:   # Fixes "socket.c:591: error: invalid application of 'sizeof' to
    # incomplete type 'struct in6_pktinfo'".  See
    # http://www.mail-archive.com/blfs-book@linuxfromscratch.org/msg13013.html
    #
    # Also adds the ability to run dhcpd as a non-root user / group
    NIX_CFLAGS_COMPILE = "-D_GNU_SOURCE -DPARANOIA";
  
    # It would automatically add -Werror, which disables build in gcc 4.4
    # due to an uninitialized variable.
    CFLAGS = "-g -O2 -Wall";
  
    buildInputs = [ perl makeWrapper ];
  
    postInstall =
      ''
  