Re: [Qemu-devel] [Spice-devel] seamless migration with spice

[Gerd Hoffmann <kraxel@redhat.com>]

On 03/12/12 19:45, Yonit Halperin wrote:
> Hi,
> On 03/12/2012 03:50 PM, Gerd Hoffmann wrote:
>>    Hi,
>>
>>> Can you explain/exemplify, why sending data as a blob (either by (a) or
>>> (b)), that is verified only by the two ends that actually use it, is a
>>> problem?
>>
>> It tends to be not very robust.  Especially when the creating/parsing is
>> done ad-hoc and the format changes now and then due to more info needing
>> to be stored later on.  The qemu migration format which has almost no
>> structure breaks now and then because of that.  Thus I'd prefer to not
>> go down this route when creating something new.
>>
>> cheers,
>>    Gerd
> 
> Exposing spice server internals to the client/qemu seems to me more
> vulnerable then sending it as a blob.

That also depends on what and how much we need to transfer.

> Nonetheless, it introduces more
> complexity to backward compatibility support and it will need to involve
> not only the capabilities/versions of the server but also those of the
> qemu/client

Backward compatibility isn't that easy both ways.

>.Which reminds me, that we also need capabilities
> negotiation for the migration protocol between the src and the destination.

If this is a hard requirement then using the vmstate channel isn't going
to work.  The vmstate is a one-way channel, no way to negotiate anything
between source and target.

cheers,
  Gerd