--- rxvt-unicode/autoconf/configure.in	2005/10/25 20:16:41	1.55
+++ rxvt-unicode/autoconf/configure.in	2005/12/23 14:46:34	1.56
@@ -1118,6 +1118,39 @@
   AC_DEFINE(HAVE_NL_LANGINFO, 1, Define if nl_langinfo(CODESET) works)
 fi
 
+AC_CACHE_CHECK(for unix-compliant filehandle passing ability, rxvt_can_pass_fds,
+[AC_TRY_LINK([
+#include <sys/types.h>
+#include <sys/socket.h>
+],[
+{
+  msghdr msg;
+  iovec iov;
+  char buf [100];
+  char data = 0;
+
+  iov.iov_base = &data;
+  iov.iov_len  = 1;
+
+  msg.msg_iov        = &iov;
+  msg.msg_iovlen     = 1;
+  msg.msg_control    = buf;
+  msg.msg_controllen = sizeof buf;
+
+  cmsghdr *cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type  = SCM_RIGHTS;
+  cmsg->cmsg_len   = 100;
+
+  *(int *)CMSG_DATA (cmsg) = 5;
+
+  return sendmsg (3, &msg, 0);
+}
+],[rxvt_can_pass_fds=yes],[rxvt_can_pass_fds=no])])
+if test x$rxvt_can_pass_fds = xyes; then
+   AC_DEFINE(HAVE_UNIX_FDPASS, 1, Define if sys/socket.h defines the necessary macros/functions for file handle passing)
+fi
+
 AC_CACHE_CHECK(for broken XIM callback, rxvt_broken_ximcb,
 [AC_COMPILE_IFELSE([
 #include <X11/Xlib.h>