[Qemu-devel] Restoring bitmaps after failed/cancelled migration

[Vladimir Sementsov-Ogievskiy]

Hi all.

We now have the following problem:

If dirty-bitmaps migration capability is enabled, persistance flag is 
dropped for all migrated bitmaps, to prevent their storing to the 
storage on inactivate. It works ok, persistence itself is migrated 
through the migration channel. But on source, bitmaps becomes not 
persistent, so if we, for some reasons, want to continue using source 
vm, we'll lose bitmaps on stop/start.

It's simple to fix it: just make bitmaps persistent again on invalidate 
[1].. But I have some questions.

1. What are possible cases? I think about the following:

a. migration cancel or fail, then invalidate
b. migration success, then qmp cont => invalidate
c. migration success, then stop/start (there was no invalidate, so [1] 
will not work)


2. Is it safe at all, saving bitmaps after inactivate, even without 
persistence?

Inactive disk implies, that it may be changed by somebody other, isn't 
it? Is it possible, that target will change the disk, and then we return 
control to the source? In this case bitmaps will be invalid. So, should 
not we drop all the bitmaps on inactivate?

--
Best regards,
Vladimir