the various kernel modules involved on unmount.
+sudo /etc/init.d/cfsd start || sudo /etc/init.d/cfsd restart # kludge
grep -q '/mnt/usb ' /proc/mounts || sudo mount /mnt/usb
sudo losetup /dev/loop0 /mnt/usb/cjwatson
grep -q '/mnt/usb/keys ' /proc/mounts || sudo mount -t ext2 /dev/loop0 /mnt/usb/keys
grep -q '/mnt/usb ' /proc/mounts || sudo mount /mnt/usb
sudo losetup /dev/loop0 /mnt/usb/cjwatson
grep -q '/mnt/usb/keys ' /proc/mounts || sudo mount -t ext2 /dev/loop0 /mnt/usb/keys
sudo umount /mnt/usb/keys
sudo losetup -d /dev/loop0
sudo umount /mnt/usb
sudo umount /mnt/usb/keys
sudo losetup -d /dev/loop0
sudo umount /mnt/usb
+sudo /etc/init.d/cfsd stop
+sudo modprobe -r nfs nfsd sd_mod usb-storage