Since the kernel 4.18 there is a possibility to speficy external
data device for dm-integrity that stores all integrity tags.
The new option --data-device in integritysetup uses this feature.
Linux kernel since version 4.18 supports automatic background
recalculation of integrity tags for dm-integrity.
This patch adds new integritysetup --integrity-recalculate options
that uses this option.
The dm-integrity target is intended to be used for authenticated
encryption through LUKS and dm-crypt.
It can be used in standalone as well; for this use case there
is a simple configuration utility called integritysetup
(similar to veritysetup to dm-verity).
