Re: [Qemu-devel] [PATCH RFC v5 07/19] virtio: allow virtio-1 queue layout

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 2 Dec 2014 16:46:28 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Dec 02, 2014 at 02:00:15PM +0100, Cornelia Huck wrote:
> > For virtio-1 devices, we allow a more complex queue layout that doesn't
> > require descriptor table and rings on a physically-contigous memory area:
> > add virtio_queue_set_rings() to allow transports to set this up.
> > 
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > ---
> >  hw/virtio/virtio.c         |   16 ++++++++++++++++
> >  include/hw/virtio/virtio.h |    2 ++
> >  2 files changed, 18 insertions(+)
> > 
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 8f69ffa..508dccf 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -96,6 +96,13 @@ static void virtqueue_init(VirtQueue *vq)
> >  {
> >      hwaddr pa = vq->pa;
> >  
> > +    if (pa == -1ULL) {
> > +        /*
> > +         * This is a virtio-1 style vq that has already been setup
> > +         * in virtio_queue_set.
> > +         */
> > +        return;
> > +    }
> >      vq->vring.desc = pa;
> >      vq->vring.avail = pa + vq->vring.num * sizeof(VRingDesc);
> >      vq->vring.used = vring_align(vq->vring.avail +
> > @@ -717,6 +724,15 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
> >      return vdev->vq[n].pa;
> >  }
> >  
> > +void virtio_queue_set_rings(VirtIODevice *vdev, int n, hwaddr desc,
> > +                            hwaddr avail, hwaddr used)
> > +{
> > +    vdev->vq[n].pa = -1ULL;
> > +    vdev->vq[n].vring.desc = desc;
> > +    vdev->vq[n].vring.avail = avail;
> > +    vdev->vq[n].vring.used = used;
> > +}
> > +
> >  void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
> >  {
> >      /* Don't allow guest to flip queue between existent and
> 
> pa == -1ULL tricks look quite ugly.
> Can't we set desc/avail/used unconditionally, and drop
> the pa value?

And have virtio_queue_get_addr() return desc? Let me see if I can come
up with a patch.