Re: [virtio-dev] Re: [RFC PATCH 4/5] virtqueue: constraints for virtqueue state

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

On 8/16/2023 10:11 AM, Jason Wang wrote:
> On Tue, Aug 15, 2023 at 7:30 PM Zhu, Lingshan <lingshan.zhu@intel.com> wrote:
>>
>>
>> On 8/15/2023 8:34 AM, Jason Wang wrote:
>>> On Mon, Aug 14, 2023 at 7:29 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>>>> This commit specifies the constraints of the virtqueue state,
>>>> and the actions should be taken by the device when SUSPEND
>>>> and DRIVER_OK is set
>>>>
>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>>> ---
>>>>    content.tex | 31 +++++++++++++++++++++++++++++++
>>>>    1 file changed, 31 insertions(+)
>>>>
>>>> diff --git a/content.tex b/content.tex
>>>> index 43bd5de..f6ac581 100644
>>>> --- a/content.tex
>>>> +++ b/content.tex
>>>> @@ -587,6 +587,37 @@ \subsection{\field{Used State} Field}
>>>>
>>>>    See also \ref{sec:Packed Virtqueues / Driver and Device Ring Wrap Counters}.
>>>>
>>>> +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>> +
>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated, the driver MUST set SUSPEND in \field{device status}
>>>> +first before getting or setting Virtqueue State of any virtqueues.
>>> I don't get why this is a must. It could be useful for debugging.
>> To avoid race conditions with the device and make the device
>> implementation easier
> replied in another thread.
>
>>>> +
>>>> +If VIRTIO_F_QUEUE_STATE has been negotiaged but VIRTIO_RING_F_PACKED not been negotiated,
>>> typo
>> yes
>>>> +the driver MUST NOT access \field{Used State} of any virtqueues, it should use the
>>>> +used index in the used ring.
>>>> +
>>>> +\devicenormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>> +
>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated but SUSPEND is not set in \field{device status},
>>>> +the device MUST ignore any accesses against Virtqueue State of any virtqueues.
>>> Btw, do we need to clarify the behavior of ring reset after suspending?
>> I think once suspended, the device should ignore resetting a queue
> This needs to be clarified.
OK, I will clarify this in the resting queue section.

This reminds me I should add: When SUSPEND is set, the \field{device 
status} is still operational for
both the device and the driver. Because after SUSPEND, the driver may 
set DRIVER_OK and the device may
set NEEDS_RESET.

Thanks
>
> Thanks
>
>
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