Re: [Qemu-devel] [RFC v2 8/8] virtio: guest driver reload for vhost-net

[Jason Wang]

On 2018年09月21日 04:39, Maxime Coquelin wrote:
> Hi Wei, Jason,
>
> On 06/19/2018 09:53 AM, Wei Xu wrote:
> > On Wed, Jun 06, 2018 at 11:48:19AM +0800, Jason Wang wrote:
> > > On 2018年06月06日 03:08, address@hidden wrote:
> > > > From: Wei Xu <address@hidden>
> > > >
> > > > last_avail, avail_wrap_count, used_idx and used_wrap_count are
> > > > needed to support vhost-net backend, all these are either 16 or
> > > > bool variables, since state.num is 64bit wide, so here it is
> > > > possible to put them to the 'num' without introducing a new case
> > > > while handling ioctl.
> > > >
> > > > Unload/Reload test has been done successfully with a patch in vhost 
> > > > kernel.
> > >
> > > You need a patch to enable vhost.
> > >
> > > And I think you can only do it for vhost-kenrel now since vhost-user
> > > protocol needs some extension I believe.
> >
> > OK.
> >
> > > > Signed-off-by: Wei Xu <address@hidden>
> > > > ---
> > > >   hw/virtio/virtio.c | 42 ++++++++++++++++++++++++++++++++++--------
> > > >   1 file changed, 34 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > > index 4543974..153f6d7 100644
> > > > --- a/hw/virtio/virtio.c
> > > > +++ b/hw/virtio/virtio.c
> > > > @@ -2862,33 +2862,59 @@ hwaddr 
> > > > virtio_queue_get_used_size(VirtIODevice *vdev, int n)
> > > >       }
> > > >   }
> > > > -uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
> > > > +uint64_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
> > > >   {
> > > > -    return vdev->vq[n].last_avail_idx;
> > > > +    uint64_t num;
> > > > +
> > > > +    num = vdev->vq[n].last_avail_idx;
> > > > +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> > > > +        num |= ((uint64_t)vdev->vq[n].avail_wrap_counter) << 16;
> > > > +        num |= ((uint64_t)vdev->vq[n].used_idx) << 32;
> > > > +        num |= ((uint64_t)vdev->vq[n].used_wrap_counter) << 48;
> > >
> > > So s.num is 32bit, I don't think this can even work.
> >
> > I mistakenly checked out s.num is 64bit, will add a new case in next 
> > version.
>
> Wouldn't be enough to just get/set avail_wrap_counter?
> Something like this so that it fits into 32 bits:
>     if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
>         num |= ((uint64_t)vdev->vq[n].avail_wrap_counter) << 31;
>     }
>
>
> Regards,
> Maxime

Yes, actually, that's what I did for vhost kernel 
(https://github.com/jasowang/net/blob/packed-host/drivers/vhost/vhost.c#L1418)

Thanks