for d in /sys/kernel/config/nullb/*; do [ -d "$d" ] && rmdir "$d"; done
modprobe -r null_blk
-modprobe null_blk nr_devices=0 || return $?
+modprobe null_blk nr_devices=0 || exit $?
for d in /sys/kernel/config/nullb/*; do
[ -d "$d" ] && rmdir "$d"
done