When no kernel source has been pointed to, first attempt to use

/lib/modules/$(uname -r)/source.  This will likely fail when building
under a mock (http://fedoraproject.org/wiki/Projects/Mock) chroot
environment since `uname -r` will report the running kernel which
likely is not the kernel in your chroot.  To cleanly handle this
we fallback to using the first kernel in your chroot.

The kernel-devel package which contains all the kernel headers and
a few build products such as Module.symver{s} is all the is required.
Full source is not needed.

config/kernel.m4

@@ -76,8 +76,14 @@ AC_DEFUN([ZFS_AC_KERNEL], [
 
 	AC_MSG_CHECKING([kernel source directory])
 	if test -z "$kernelsrc"; then
-		sourcelink=`ls -1d /usr/src/kernels/* /usr/src/linux-* \
-		            2>/dev/null | grep -v obj | tail -1`
+		headersdir="/lib/modules/$(uname -r)/build"
+		if test -e "$headersdir"; then
+			sourcelink=$(readlink -f "$headersdir")
+		else
+			sourcelink=$(ls -1d /usr/src/kernels/* \
+				     /usr/src/linux-* \
+			             2>/dev/null | grep -v obj | tail -1)
+		fi
 
 		if test -e $sourcelink; then
 			kernelsrc=`readlink -f ${sourcelink}`