Adding grub2 mkconfig support patch

Added simply for convenience until this, or an equivilant, change
is merged in the upstream grub2 source.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #847

patches/grub-mkconfig-zfs-support.diff

@@ -0,0 +1,31 @@
+diff -up ./util/grub-mkconfig.in.original ./util/grub-mkconfig.in
+--- ./util/grub-mkconfig.in.original	2012-03-27 13:03:49.475388000 -0700
++++ ./util/grub-mkconfig.in	2012-03-27 13:06:38.948080000 -0700
+@@ -140,9 +140,24 @@ if test -e ${GRUB_PREFIX}/device.map ; t
+   ${grub_mkdevicemap}
+ fi
+ 
+-# Device containing our userland.  Typically used for root= parameter.
+-GRUB_DEVICE="`${grub_probe} --target=device /`"
+-GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true
++# Attempt to detect if the root file system is in ZFS first
++unset GRUB_DEVICE
++unset GRUB_DEVICE_BOOT
++getzfsgrubdevice() {
++    mount | while read dev dummy mntpnt dummy2 fstype rest ; do
++        if [ -n "$GRUB_DEVICE" ] ; then break ; fi
++        if [ "$fstype" != "zfs" ] ; then continue ; fi
++        if [ "$mntpnt" != "/" ] ; then continue ; fi
++        GRUB_DEVICE=`fstab-decode echo "$dev"`
++        GRUB_DEVICE="ZFS=$GRUB_DEVICE" ; echo "$GRUB_DEVICE" ; break
++    done
++}
++GRUB_DEVICE=`getzfsgrubdevice`
++if [ -z "$GRUB_DEVICE" ] ; then
++    # Device containing our userland.  Typically used for root= parameter.
++    GRUB_DEVICE="`${grub_probe} --target=device /`"
++    GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true
++fi
+ 
+ # Device containing our /boot partition.  Usually the same as GRUB_DEVICE.
+ GRUB_DEVICE_BOOT="`${grub_probe} --target=device /boot`"