Re: [PATCH] Update virtio to latest ABI

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

Avi Kivity wrote:
> Anthony Liguori wrote:
>> This patch updates KVM's virtio implementation to the latest virtio 
>> ABI.  This
>> includes a change in the network header and support for reset.
>>
>> With this patch, the block and network driver from Rusty's latest 
>> queue are
>> functioning.  Module unload and reload work and I no longer see an 
>> error when
>> repeatedly bringing a network interface up and down.
>>
>>   
>
> Applied, thanks.
>
> 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.

Regards,

Anthony Liguori



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