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

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

On 8/15/2023 8:37 AM, Jason Wang wrote:
> On Tue, Aug 15, 2023 at 8:26 AM Jason Wang <jasowang@redhat.com> wrote:
>> On Mon, Aug 14, 2023 at 7:29 PM 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.
To allow terminate a live migration process or resume from a failed live 
migration,
we allow DRIVER_OK to clear SUSPEND, in patch 1.

Thanks
>
> 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
>>>


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