# cd /usr/src/
# patch -p3 < /anywhere/unionfs-p19-20070504.diff
# cp /usr/src/sys/fs/unionfs/union.h /usr/include/fs/unionfs/
# cd /usr/src/sbin/mount_unionfs/
# make obj depend && make && make install
# make clean
# cd /usr/src
# make buildkernel
# make installkernel
# shutdown -r now