Re: [Qemu-devel] [RFC 0/2] Disable hotplug during migration

[Juan Quintela <quintela@redhat.com>]

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Juan Quintela (quintela@redhat.com) wrote:
>> Hi
>> 
>> This series disable hotplug/unplug during migration.  Thank to Markus
>> for explaining where I had to put the checks.  Why?  Because during
>> migration we will fail if there are changes.  For instance, in
>> postcopy, if we add a memory region, we would failing.  Same for other
>> devices if they are not setup exactly the same on destination.
>> 
>> Iidea would be to disable it, andthen enable for the thing that we know that work.
>> 
>> This series are on top of my previous RAMState v2 serie.
>> 
>> Commets, please?
>
> So I think this is probably a good idea, but we should ask Li Zhijian who added
> migration_bitmap_extend if the reason for adding it was because they
> needed the hot add to work.
> cc'd.

I guess that the problem for them is that the bitmap size was wrong
after memory resizing.  But I don't know if this has ever worked.


> IMHO we really need a 'configuration change mutex' that you can take
> to stop any changes in the VM hardware, and that would probably reduce
> a lot of the places that hold the BQL for just stopping changes.

That was the previous patch.  With that one, you can't add/remove
hardware during migration.

Later, Juan.