Re: [Qemu-devel] Re: [PATCH RFC] virtio: add features qdev property

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Dec 14, 2009 at 09:40:28PM +0100, Gerd Hoffmann wrote:
> On 12/14/09 20:17, Michael S. Tsirkin wrote:
>> On Mon, Dec 14, 2009 at 06:18:29PM +0100, Gerd Hoffmann wrote:
>>> On 12/14/09 17:23, Michael S. Tsirkin wrote:
>>>> On Mon, Dec 14, 2009 at 04:01:33PM +0100, Gerd Hoffmann wrote:
>>>> So how do you do this?
>>>> Assume we have -disable_hw_csum.
>>>> We want new machine type to have it off, right?
>>>> But now you run qemu on host which does
>>>> not support hw_csum. With your suggestion
>>>> it will not enable hw csum?
>>>
>>> I have trouble getting the setup you are talking about ...
>>>
>>> Sounds like hw_csum could be enabled/disabled depending on the hardware
>>> capabilities on the host.  Is that correct?
>>>
>>> cheers,
>>>    Gerd
>>
>> This currently depends on version of tun driver in the host.
>
> So this has nothing to do with -M pc-0.11 backward compatibility, right?  

Yes, this does. With 0.11 you must not expose this even
if supported by host. Otherwise you wnt be able to migrate to 0.11.

>  You'll hit this when migrating 0.12 -> 0.12 with different host  
> kernels, right?  And the common bit here is that both issues can be  
> handled by configuring virtio feature bits via properties, right?

Yes.

> What was the question again?
>
> cheers,
>   Gerd


What do we put in e.g. 0.11 compat? Any features we enable
there might not be supported by host.

-- 
MST