Re: [Qemu-devel] [PATCH v4 0/2] virtio: Move host features to backends

[Cornelia Huck]

On Tue, 28 Apr 2015 15:05:47 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Tue, Apr 28, 2015 at 01:52:40PM +0100, Peter Maydell wrote:
> > On 28 April 2015 at 13:48, Michael S. Tsirkin <address@hidden> wrote:
> > > On Tue, Apr 28, 2015 at 07:51:11PM +0800, address@hidden wrote:
> > >> From: Shannon Zhao <address@hidden>
> > >> Here we move the host features to backends, involving
> > >> DEFINE_VIRTIO_NET_FEATURES, DEFINE_VIRTIO_SCSI_FEATURES. So the
> > >> virtio-mmio devices could have the host freatures, and this has a great
> > >> performance improvement to virtio-mmio, especially to virtio-net-device.
> > >
> > > Can you move COMMON_FEATURES too please?
> > 
> > I think that would be wrong -- COMMON_FEATURES are transport features,
> > not backend-specific features, so they belong on the transports
> > (and on the convenience wrappers), not the backends.
> > 
> > thanks
> > -- PMM
> 
> Hmm you are right. The problem is with s390 which
> puts this DEFINE_VIRTIO_COMMON_FEATURES in all devices.

All save virtio-blk. There were some problems when switching on
event_idx on virtio-blk, IIRC.

The other transport add DEFINE_VIRTIO_COMMON FEATURES in their base
class. Because of the not-quite-understood problem with virtio-blk, we
couldn't do that with s390-virtio.