On Tue, 14 Apr 2015 10:42:56 +0930
Rusty Russell [off-list ref] wrote:

"Michael S. Tsirkin" [off-list ref] writes:

quoted

On Wed, Apr 01, 2015 at 02:57:35PM +0200, Michael S. Tsirkin wrote:

quoted

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?