MTV-2307 (customer case 04093754) found apparent data consistency problems when copying a Windows guest over from VMware to CNV, when the PVC on the target was backed by Dell Powermax storage. We're still not clear why this is happening.

However one problem this revealed in virt-v2v was there is no checksumming done on the image as it is written out. This would allows us to find out if corruption was happening before, during or after conversion, which might help to narrow it down.

Furthermore I have added some debugging to nbdkit so we can tell if various system calls are failing (which would have failed silently before).

This requires various changes in virt-v2v, libnbd & nbdkit.