Re: [PATCH] Update virtio to latest ABI

Anthony Liguori
2008-01-28T16:01:02Z

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