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Date: Mon, 14 Dec 2009 22:24:49 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] Re: [PATCH RFC] virtio: add features qdev property
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org

On 12/14/09 22:14, Michael S. Tsirkin wrote:
> On Mon, Dec 14, 2009 at 10:12:14PM +0100, Gerd Hoffmann wrote:
>> On 12/14/09 21:43, Michael S. Tsirkin wrote:
>>> What do we put in e.g. 0.11 compat? Any features we enable
>>> there might not be supported by host.
>>
>> compat properties as usual?
>>
>> Sorry, I still fail to see your problem.
>>
>> You'll have a 'disable' bitmap.  Fill it via 'features=<bitmap-prop>'.
>> Or using separate properties for each feature.
>> qemu goes figure host_features.  When done it masks out the features
>> disabled via properties.  The result is used as final feature bitmap.
>>
>> -M pc-0.11 will disable hw_checksum
>> management software can do it too via -device virtio-net-pci,... if some
>> machines in the pool don't support it.  And of course qemu will disable
>> it on its own in case the host kernel doesn't support it.
>>
>> cheers,
>>    Gerd
>
> management is always behind :).  Imagine a new and improved qemu. I run
> old management.  I expect to see old properties, but old management can
> not disable new ones :)

If management can't deal with 0.12 features it should use -M pc-0.11

cheers,
   Gerd