Re: [RFC 7/11] virtio_pci: new, capability-aware driver.

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2012-01-12 at 00:02 +0200, Michael S. Tsirkin wrote:
> > We could probably have a helper library for sending control messages
> > which could handle waiting for a ring slot to be free (practically
> > always the case on control queues), writing the message, sending it
> and
> > waiting for a status queue confirmation message.
> > 
> > Cheers,
> > Ben.
> > 
> 
> Look, we have a race currently. Let us not tie a bug fix to a huge
> rewrite with unclear performance benefits, please.

Well, if we change endian, change the way config works, I think we are
doing enough dramatic changes to go all the way and change the ring
format too.

I don't think there's anything "unclear" about improving the rings in
the direction that all network cards have been chosing so far :-) But
for the control ring, performance is clearly not an issue.

I also like the simplicity of immediate data, it limits the failure
path, no allocation -does- make it easier, not having to wait for the
previous buffer to be complete if you pre-allocate etc...

In any case, if we do a lot of changes at the same time, we are probably
better off cutting the cord and making an incompatible vfio v2 with a
new set of drivers.

Having to deal with all the variants in a single driver will result in
unmaintainable drivers imho.

Cheers,
Ben.