From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [RFC 7/11] virtio_pci: new, capability-aware driver.
Date: Wed, 11 Jan 2012 17:45:15 +0200
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Pawel Moll <pawel.moll@arm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, virtualization <virtualization@lists.linux-foundation.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Sasha Levin <levinsasha928@gmail.com>
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On Wed, Jan 11, 2012 at 09:28:27AM -0600, Anthony Liguori wrote:
> On 01/11/2012 09:21 AM, Michael S. Tsirkin wrote:
> >On Wed, Jan 11, 2012 at 09:15:49AM -0600, Anthony Liguori wrote:
> >>>This is similar to what we have now. But it's still buggy: e.g. if guest
> >>>updates MAC byte by byte, we have no way to know when it's done doing
> >>>so.
> >>
> >>This is no different than a normal network card.  You have to use a
> >>secondary register to trigger an update.
> >>
> >>Regards,
> >>
> >>Anthony Liguori
> >
> >Possible but doesn't let us layer nicely to allow unchanged drivers
> >that work with all transports (new pci, old pci, non pci).
> 
> If we declare config space LE, then we have to touch all drivers.
> There's no way around it because the virtio API is byte-based, not
> word based.

Fine but don't we want to be compatible with old hypervisors?

> This is why I'm suggesting making the virtio API (and then the
> virtio-pci ABI) word based.  It gives us the flexibility to make
> endianness a property of the transport and not a property of the
> devices.
> 
> Regards,
> 
> Anthony Liguori

Some fields are 64 bit, this is still tricky to do atomically.
What's the objection to using a config VQ?