From: Anthony G. Basile <blueness@gentoo.org>

ipsec-tools tries to make use of the kernel headers in /usr/src/linux/include/linux.
This is not a good idea because these are not the system exported linux header files.
Unfortunately the configure.ac option which says where to look for these headers
doesn't point to the directory itself, usually /usr/include/linux, but to its parent!

Our solution then, although less than satifying, is to remove the --with-kernel-headers
switch and hard code KERNEL_INCLUDE="/usr/include".

diff -Naur ipsec-tools-0.8.0.orig/configure.ac ipsec-tools-0.8.0/configure.ac
--- ipsec-tools-0.8.0.orig/configure.ac	2012-03-05 18:46:54.000000000 -0500
+++ ipsec-tools-0.8.0/configure.ac	2012-03-05 18:53:56.000000000 -0500
@@ -66,18 +66,11 @@
 
 case "$host_os" in
  *linux*)
-    AC_ARG_WITH(kernel-headers,
-	AC_HELP_STRING([--with-kernel-headers=/lib/modules/<uname>/build/include],
-		       [where your Linux Kernel headers are installed]),
-	    [ KERNEL_INCLUDE="$with_kernel_headers" 
-	      CONFIGURE_AMFLAGS="--with-kernel-headers=$with_kernel_headers"
-	      AC_SUBST(CONFIGURE_AMFLAGS) ],
-	    [ KERNEL_INCLUDE="/lib/modules/`uname -r`/build/include" ])
-
+    KERNEL_INCLUDE="/usr/include"
     AC_CHECK_HEADER($KERNEL_INCLUDE/linux/pfkeyv2.h, ,
 	[ AC_CHECK_HEADER(/usr/src/linux/include/linux/pfkeyv2.h,
 	  KERNEL_INCLUDE=/usr/src/linux/include ,
-	  [ AC_MSG_ERROR([Unable to find linux-2.6 kernel headers. Aborting.]) ] ) ] )
+	  [ AC_MSG_ERROR([Unable to find linux kernel headers. Aborting.]) ] ) ] )
     AC_SUBST(KERNEL_INCLUDE)
     # We need the configure script to run with correct kernel headers.
     # However we don't want to point to kernel source tree in compile time,