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Re: [Qemu-block] [PATCH 3/4] savevm: fix savevm after migration

From: Paolo Bonzini
Subject: Re: [Qemu-block] [PATCH 3/4] savevm: fix savevm after migration
Date: Wed, 29 Mar 2017 17:53:15 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 29/03/2017 17:29, Dr. David Alan Gilbert wrote:
>>> 'abort' is not very good too I think. migration is completed, nothing to
>>> abort.. (may be successful migration to file for suspend, some kind of
>>> vm cloning, etc)
>> There is already migrate_cancel.  Does it make sense to make it
>> reactivate fds if migration is completed?
> It's potentially racy to do that.
> Imagine if your migration is almost finished and you issue a migrate_cancel,
> what happens?
> Maybe it cancelled it.
> Maybe it just completed in time - and you really better not be accessing
> the disks on the source unless you're sure the destination isn't running.

If you want to avoid races, you probably have to use -S anyway on the
destination and do more handshaking between source and destination.  But
yes, just to be safe it'd be better to add a new flag (-f for HMP,
'cancel-completed-migration':true for QMP or something like that).


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