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Date: Thu, 28 May 2009 07:56:54 -0500
From: Anthony Liguori <aliguori@us.ibm.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH] Change virtio-console to
	PCI_CLASS_SERIAL_OTHER
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	<200905281353.50463.paul@codesourcery.com>
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To: Paul Brook <paul@codesourcery.com>
Cc: Mark McLoughlin <markmc@redhat.com>, Dor Laor <dlaor@redhat.com>, ajax@redhat.com, qemu-devel@nongnu.org

Paul Brook wrote:
> On Wednesday 27 May 2009, Mark McLoughlin wrote:
>   
>> On Wed, 2009-05-27 at 09:21 -0500, Anthony Liguori wrote:
>>     
>>> We need a mechanism to toggle this for both this and virtio-blk.  The
>>> reason a toggle is needed is so that 0.11 can create the same device
>>> model as 0.10.
>>>       
>> Okay, so the scenario is:
>>
>>   - 0.10 guest running on source machine
>>
>>   - migrate to dest machine running 0.11
>>
>>   - the device model cannot change or the guest OS will get confused
>>     
>
> IMHO think the only sane response is "don't do that". Trying to support 
> migration between different qemu versions just isn't worth the pain.
>   

It is very worth the pain.  I consider it a core requirement.

Supporting legacy workloads is an important aspect of virtualization. 
If we cannot provide a consistent environment as we evolve over time,
then we cannot support legacy workloads.

It really isn't that hard, it just requires that we exercise care.

Regards,

Anthony Liguori

> Paul
>