Re: [virtio-dev] Re: [RFC PATCH 3/5] virtio: The actions by the device upon SUSPEND

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 8/15/2023 8:29 AM, Jason Wang wrote:
> On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
> > This commit specifies the actions to be taken by the device upon
> > SUSPEND.
> >
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> > ---
> >   content.tex | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 074f43e..43bd5de 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -96,6 +96,15 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >   If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear SUSPEND
> >   and resumes operation upon DRIVER_OK.
> >
> > +If VIRTIO_F_SUSPEND is negotiated, when SUSPEND is set, the device MUST perform the following operations:
> > +\begin{itemize}
> > +\item Stop comsuming any descriptors
> Typo.
yes will fix
> > +\item Mark all finished descriptors as used and send used buffer notification to the driver
> What happens to the unfinished descriptors?
still in the descriptors table or considered as in-flight, we will post 
a patch tracking in-flight descriptors.
> > +\item Record Virtqueue State of each enabled virtqueue, see section \ref{sec:Virtqueues / Virtqueue State}
> This basically means those states are only available after suspending
> or not? It would be still useful for debugging if we allow it without
> suspending.
Yes, for now only allow to read/write the virtqueue state after setting
SUSPEND, this is to avoid race conditions with the device.

Still can suspend then collect the idx for debugging?
> > +\item Pause its operation and preserve all configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
> We probably need to define the "pause" here (e.g what happens to the
> inflight descriptors).
Shall we say: freeze both its data-plane and control-plane?
> Thanks
>
> > +\item Present SUSPEND in \field{device status}
> > +\end{itemize}
> > +
> >   \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
> >
> >   Each virtio device offers all the features it understands.  During
> > --
> > 2.35.3
>
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