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

[Jason Wang <jasowang@redhat.com>]

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

> +
> +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
>