linux-kernel - Re: [PATCH v3 0/6] virtio

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Message-ID: <20150414102438.11d12347.cornelia.huck@de.ibm.com>
Date:	Tue, 14 Apr 2015 10:24:38 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org, Pawel Moll <pawel.moll@....com>,
	virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 0/6] virtio_balloon: virtio 1 support

On Tue, 14 Apr 2015 10:42:56 +0930
Rusty Russell <rusty@...tcorp.com.au> wrote:

> "Michael S. Tsirkin" <mst@...hat.com> writes:
> > On Wed, Apr 01, 2015 at 02:57:35PM +0200, Michael S. Tsirkin wrote:
> >> Virtio 1.0 doesn't include a modern balloon device.  At some point we'll likely
> >> define an incompatible interface with a different ID and different
> >> semantics.  But for now, it's not a big effort to support a transitional
> >> balloon device: this has the advantage of supporting existing drivers,
> >> transparently, as well as transports that don't allow mixing virtio 0 and
> >> virtio 1 devices. And balloon is an easy device to test, so it's also useful
> >> for people to test virtio core handling of transitional devices.
> >> 
> >> The only interface issue is with the stats buffer, which has misaligned
> >> fields. We could leave it as is, but this sets a bad precedent that
> >> others might copy by mistake.
> >> 
> >> As we need to change stats code to do byteswaps for virtio 1.0, it seems easy
> >> to fix by prepending a 6 byte reserved field.  I also had to change config
> >> structure field types from __le32 to __u32 to match other devices. This means
> >> we need a couple of __force tags for legacy path but that seems minor.
> >
> > Rusty, what are your thoughts here?
> > How about merging this for 4.1?
> 
> I disagree with making any changes, other than allowing it to be used
> with VIRTIO_F_VERSION_1.
> 
> However it doesn't seem to bother anyone else, so I've applied it for
> 4.1.

I'm still not really convinced about the stats change either, FWIW.
Still time to reconsider? And should we perhaps wait with merging until
the spec change allowing version 1 has been accepted?

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