Re: [Qemu-devel] [PATCH v2 1/2] virtio: Add function to check whether backend supports VIRTIO_1

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Sep 09, 2016 at 08:00:31PM +0300, Marcel Apfelbaum wrote:
> On 09/09/2016 04:10 PM, Maxime Coquelin wrote:
> > This patch adds virtio_test_backend_virtio_1() function to
> > check whether backend supports VIRTIO_F_VERSION_1 before the
> > negociation takes place.
> > 
> > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > Cc: Marcel Apfelbaum <marcel@redhat.com>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> > Cc: qemu-stable@nongnu.org
> > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > ---
> >  hw/virtio/virtio.c         | 13 +++++++++++++
> >  include/hw/virtio/virtio.h |  1 +
> >  2 files changed, 14 insertions(+)
> > 
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 74c085c..8b30b69 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -1481,6 +1481,19 @@ void virtio_vmstate_save(QEMUFile *f, void *opaque, size_t size)
> >      virtio_save(VIRTIO_DEVICE(opaque), f);
> >  }
> > 
> > +bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp)
> > +{
> > +    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
> > +    uint64_t feature;
> > +
> 
> I would set "feature = 0" even if doesn't really matter.
> Anyway:
> 
> Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
> 
> Thanks,
> Marcel

why wouldn't it matter? Looks like an uninitialized variable to me.

> > +    virtio_add_feature(&feature, VIRTIO_F_VERSION_1);
> > +
> > +    assert(k->get_features != NULL);
> > +    feature = k->get_features(vdev, feature, errp);
> > +
> > +    return virtio_has_feature(feature, VIRTIO_F_VERSION_1);
> > +}
> > +
> >  static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val)
> >  {
> >      VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index d2490c1..3a31754 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -235,6 +235,7 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val);
> >  void virtio_reset(void *opaque);
> >  void virtio_update_irq(VirtIODevice *vdev);
> >  int virtio_set_features(VirtIODevice *vdev, uint64_t val);
> > +bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp);
> > 
> >  /* Base devices.  */
> >  typedef struct VirtIOBlkConf VirtIOBlkConf;
> >