Modify virt-v2v to use nbdcopy --blkhash flag, when virt-v2v is run in verbose mode. This will cause nbdcopy to print the blkhash of each disk image. This would allow us to check the blkhash later, which would let us know if corruption happened during or after conversion.

Note the blkhash algorithm is described here: https://gitlab.com/nirs/blkhash/

Upstream commit:
https://github.com/libguestfs/virt-v2v/commit/cffd129d8fd47554255d52ad611d58a30b6b9951