Re: [PATCH] Update virtio to latest ABI

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>>>
>>> This ABI breakage is worrying.  While it is expected to take some 
>>> time for the ABI to congeal, we need some way to prevent mismatched 
>>> guests and hosts from running.  Perhaps something like the kvm abi 
>>> version, storedin the pci revision field?  Keep incrementing it 
>>> until we are satisfied, then use feature bits to add functionality.
>>
>> This breakage wasn't actually necessary.  We could have used a 
>> feature bit to indicate the additional net config field.  In the very 
>> least, the additional net config field could have been added to the 
>> end of the config space so that old guests kept working that didn't 
>> use GSO.
>>
>> I don't think we need another mechanism to avoid breakages in the 
>> future.  I think we have to declare that whatever ships in 2.6.25 is 
>> the stable ABI and make sure not to break it again in the future.
>
> I'm worried about the ramp up to 2.6.25 causing confusion among users 
> as before that things will break left and right, if we don't provide a 
> tighter check.
>

Well, using the PCI revision ID isn't a bad idea.  It wouldn't have 
helped this last problem because that was an ABI break in the network 
driver and we really can't indicate a ABI break in the PCI driver for 
any possibly virtio device.  However, if we change the PCI ABI, we can 
be a little more friendly about it.

Just sent out patches.

Regards,

Anthony Liguori

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