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SubjectRe: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace
On Tue, Jun 29, 2021 at 11:29 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2021/6/29 上午10:26, Yongji Xie 写道:
> > On Mon, Jun 28, 2021 at 12:40 PM Jason Wang <jasowang@redhat.com> 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.
>

OK, I see. If so, I prefer to only use noreply for set_status(). We do
not set the status bit if the message is failed. In this way, we don't
need to change lots of virtio core codes to handle the failure of
set_status()/get_status().

Thanks,
Yongji

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