Re: [RFC PATCH 1/5] virtio: introduce SUSPEND bit in device status

[Jason Wang <jasowang@redhat.com>]

On Tue, Aug 15, 2023 at 8:26âAM Jason Wang <jasowang@redhat.com> wrote:
>
> On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
> >
> > This patch introudces a new status bit in the device status: SUSPEND.
> >
> > This SUSPEND bit can be used by the driver to suspend a device,
> > in order to stablize the device states and virtqueue states.
> >
> > Its main use case is live migration.
>
> I think patch 3 needs to be squashed into this one.
>
> >
> > 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 | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 0a62dce..1bb4401 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -47,6 +47,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >  \item[DRIVER_OK (4)] Indicates that the driver is set up and ready to
> >    drive the device.
> >
> > +\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the
> > +  device has been suspended by the driver.
> > +
> >  \item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced
> >    an error from which it can't recover.
> >  \end{description}
> > @@ -73,6 +76,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >  recover by issuing a reset.
> >  \end{note}
> >
> > +The driver MUST NOT set SUSPEND if FEATURES_OK is not set.
> > +
> > +When set SUSPEND, the driver MUST re-read \field{device status} to ensure the SUSPEND bit is set.
> > +
> >  \devicenormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field}
> >
> >  The device MUST NOT consume buffers or send any used buffer
> > @@ -82,6 +89,13 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >  that a reset is needed.  If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device
> >  MUST send a device configuration change notification to the driver.
> >
> > +The device MUST ignore SUSPEND if FEATURES_OK is not set.
>
> Is there any value to allow SUSPEND to be set without DRIVER_OK?
>
> > +
> > +The deivce MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated.
>
> typo.
>
> Thanks

Btw, it's not clear to me if driver is allowed to clear this bit.

Thanks

>
> > +
> > +If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear SUSPEND
> > +and resumes operation upon DRIVER_OK.
> > +
> >  \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
> >
> >  Each virtio device offers all the features it understands.  During
> > @@ -872,6 +886,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> >         \ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
> >         handling features reserved for future use.
> >
> > +  \item[VIRTIO_F_SUSPEND(41)] This feature indicates that the driver can
> > +   SUSPEND the device.
> > +   See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}.
> > +
> >  \end{description}
> >
> >  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> > --
> > 2.35.3
> >