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

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-devel] Restoring bitmaps after failed/cancelled migration
Date: Mon, 14 May 2018 12:55:25 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

12.05.2018 00:23, John Snow wrote:

On 04/18/2018 10:00 AM, Vladimir Sementsov-Ogievskiy wrote:
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.

Sorry for not following along more carefully, which kind of migration
are we talking about in this case?

Any migration with dirty-bitmaps capability enabled..

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

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,

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