@benapetr This is driven by hacky logic from 16 years ago:
- on revert, unserialize the previous state, and update the VM record with its saved values. As we do not want to modify that each time we add a field in the datamodel, use some low-level database functions to iterate over the fields of a record. Not very nice as it makes some assumptions on the database layer, but seems to work allright and I don't think that database layer will change a lot in the future.
I think it might be a good idea to add a revert rpc call to the storage interface that xapi can call to, with a backup to use the current logic if necessary; xapi should be able to clean up the database afterwards. I'll ask other maintainers about this or possible alternatives, but since SMAPIv1 is considered deprecated, I doubt it will happen.
I have to say that SMAPIv3 was finally fixed upstream on June by Xenserver (migrations were finally done!) and XCP-ng should get the update that fixes it in the coming weeks. Given this, I would encourage you to take all the learnings you've acquired while doing the driver and porting it to SMAPIv3. SMAPIv1 just simply has too many problems, some of them are architectural, so in general xenserver and xcp-ng maintainers would like to see it finally go away.
for now I am still targetting XCP-ng 8.2 as that's what I use in production, and I haven't seen many SMAPIv3 drivers there.
8.2 is out of support for xenserver, and for xcp-ng yesterday was the last day it was supported, you really should update 
