grub: fallback for failed grub-probe on zfs in mkconfig

srcpkgs/grub/patches/mkconfig_zfs.patch

@@ -0,0 +1,12 @@
+--- ./util/grub.d/10_linux.in	2015-01-19 13:30:29.490090317 +0200
++++ ./util/grub.d/10_linux.in	2015-01-19 13:29:41.234754594 +0200
+@@ -67,6 +67,9 @@
+     xzfs)
+ 	rpool=`${grub_probe} --device ${GRUB_DEVICE} --target=fs_label 2>/dev/null || true`
+ 	bootfs="`make_system_path_relative_to_its_root / | sed -e "s,@$,,"`"
++	if [ -z "${rpool}" ]; then
++		rpool=$(zfs list -Ho name -t filesystem | grep -m1 "${bootfs}$" | sed 's/\/.*//')
++	fi
+ 	LINUX_ROOT_DEVICE="ZFS=${rpool}${bootfs}"
+ 	;;
+ esac