Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

[Jason Wang]

在 2021/6/29 上午10:26, Yongji Xie 写道:
> On Mon, Jun 28, 2021 at 12:40 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > 在 2021/6/25 下午12:19, Yongji Xie 写道:
> > > > 2b) for set_status(): simply relay the message to userspace, reply is no
> > > > needed. Userspace will use a command to update the status when the
> > > > datapath is stop. The the status could be fetched via get_stats().
> > > >
> > > > 2b looks more spec complaint.
> > > Looks good to me. And I think we can use the reply of the message to
> > > update the status instead of introducing a new command.
> > Just notice this part in virtio_finalize_features():
> >
> >           virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
> >           status = dev->config->get_status(dev);
> >           if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> >
> > So we no reply doesn't work for FEATURES_OK.
> >
> > So my understanding is:
> >
> > 1) We must not use noreply for set_status()
> > 2) We can use noreply for get_status(), but it requires a new ioctl to
> > update the status.
> >
> > So it looks to me we need synchronize for both get_status() and
> > set_status().
> We should not send messages to userspace in the FEATURES_OK case. So
> the synchronization is not necessary.


As discussed previously, there could be a device that mandates some 
features (VIRTIO_F_RING_PACKED). So it can choose to not accept 
FEATURES_OK is packed virtqueue is not negotiated.

In this case we need to relay the message to userspace.

Thanks


> Thanks,
> Yongji