# we wait up to 15 seconds (+/- a few) for usb-storage to settle down
for loop in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15; do
    device=$(find_backing_device)
    [ -n "$device" ] && break
    sleep 1
done
[ -z "$device" ] && exit 0