Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR

[Anthony Liguori <aliguori@us.ibm.com>]

Rusty Russell <rusty@rustcorp.com.au> writes:

> Anthony Liguori <aliguori@us.ibm.com> writes:
>> Forcing a guest driver change is a really big
>> deal and I see no reason to do that unless there's a compelling reason
>> to.
>>
>> So we're stuck with the 1.0 config layout for a very long time.
>
> We definitely must not force a guest change.  The explicit aim of the
> standard is that "legacy" and 1.0 be backward compatible.  One
> deliverable is a document detailing how this is done (effectively a
> summary of changes between what we have and 1.0).

If 2.0 is fully backwards compatible, great.  It seems like such a
difference that that would be impossible but I need to investigate
further.

Regards,

Anthony Liguori

>
> It's a delicate balancing act.  My plan is to accompany any changes in
> the standard with a qemu implementation, so we can see how painful those
> changes are.  And if there are performance implications, measure them.
>
> Cheers,
> Rusty.
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