[PATCH 1/4] vdpa: Add stop operation

Si-Wei Liu
Tue, 24 May 2022 00:01:27 -0000

On 5/23/2022 4:54 PM, Si-Wei Liu wrote:
>
>
> On 5/23/2022 12:20 PM, Eugenio Perez Martin wrote:
>> On Sat, May 21, 2022 at 12:13 PM Si-Wei Liu <si-wei.liu at
oracle.com>
>> wrote:
>>>
>>>
>>> On 5/20/2022 10:23 AM, Eugenio P?rez wrote:
>>>> This operation is optional: It it's not implemented,
backend
>>>> feature bit
>>>> will not be exposed.
>>>>
>>>> Signed-off-by: Eugenio P?rez <eperezma at redhat.com>
>>>> ---
>>>> ?? include/linux/vdpa.h | 6 ++++++
>>>> ?? 1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
>>>> index 15af802d41c4..ddfebc4e1e01 100644
>>>> --- a/include/linux/vdpa.h
>>>> +++ b/include/linux/vdpa.h
>>>> @@ -215,6 +215,11 @@ struct vdpa_map_file {
>>>> ??? * @reset:????????????????? Reset device
>>>> ??? *????????????????????????? @vdev: vdpa device
>>>> ??? *????????????????????????? Returns integer: success (0) or
>>>> error (< 0)
>>>> + * @stop:??????????????????? Stop or resume the device
(optional,
>>>> but it must
>>>> + *?????????????????????????? be implemented if require device
stop)
>>>> + *?????????????????????????? @vdev: vdpa device
>>>> + *?????????????????????????? @stop: stop (true), not stop
(false)
>>>> + *?????????????????????????? Returns integer: success (0) or
error
>>>> (< 0)
>>> Is this uAPI meant to address all use cases described in the full
blown
>>> _F_STOP virtio spec proposal, such as:
>>>
>>> --------------%<--------------
>>>
>>> ...... the device MUST finish any in flight
>>> operations after the driver writes STOP.? Depending on the device,
it
>>> can do it
>>> in many ways as long as the driver can recover its normal operation
>>> if it
>>> resumes the device without the need of resetting it:
>>>
>>> - Drain and wait for the completion of all pending requests until a
>>> ??? convenient avail descriptor. Ignore any other posterior
descriptor.
>>> - Return a device-specific failure for these descriptors, so the
driver
>>> ??? can choose to retry or to cancel them.
>>> - Mark them as done even if they are not, if the kind of device can
>>> ??? assume to lose them.
>>> --------------%<--------------
>>>
>> Right, this is totally underspecified in this series.
>>
>> I'll expand on it in the next version, but that text proposed to
>> virtio-comment was complicated and misleading. I find better to get
>> the previous version description. Would the next description work?
>>
>> ```
>> After the return of ioctl, the device MUST finish any pending
>> operations like
>> in flight requests. It must also preserve all the necessary state (the
>> virtqueue vring base plus the possible device specific states)
> Hmmm, "possible device specific states" is a bit vague. Does it
> require the device to save any device internal state that is not
> defined in the virtio spec - such as any failed in-flight requests to
> resubmit upon resume? Or you would lean on SVQ to intercept it in
> depth and save it with some other means? I think network device also
> has internal state such as flow steering state that needs bookkeeping
> as well.
Noted that I understand you may introduce additional feature call
similar to VHOST_USER_GET_INFLIGHT_FD for (failed) in-flight request,
but since that's is a get interface, I assume the actual state
preserving should still take place in this STOP call.

-Siwei

>
> A follow-up question is what is the use of the `stop` argument of
> false, does it require the device to support resume? I seem to recall
> this is something to abandon in favor of device reset plus setting
> queue base/addr after. Or it's just a optional feature that may be
> device specific (if one can do so in simple way).
>
> -Siwei
>
>> ? that is required
>> for restoring in the future.
>>
>> In the future, we will provide features similar to
>> VHOST_USER_GET_INFLIGHT_FD
>> so the device can save pending operations.
>> ```
>>
>> Thanks for pointing it out!
>>
>>
>>
>>
>>
>>> E.g. do I assume correctly all in flight requests are flushed after
>>> return from this uAPI call? Or some of pending requests may be
subject
>>> to loss or failure? How does the caller/user specify these various
>>> options (if there are) for device stop?
>>>
>>> BTW, it would be nice to add the corresponding support to
vdpa_sim_blk
>>> as well to demo the stop handling. To just show it on vdpa-sim-net
IMHO
>>> is perhaps not so convincing.
>>>
>>> -Siwei
>>>
>>>> ??? * @get_config_size: Get the size of the configuration space
>>>> includes
>>>> ??? *????????????????????????? fields that are conditional on
>>>> feature bits.
>>>> ??? *????????????????????????? @vdev: vdpa device
>>>> @@ -316,6 +321,7 @@ struct vdpa_config_ops {
>>>> ?????? u8 (*get_status)(struct vdpa_device *vdev);
>>>> ?????? void (*set_status)(struct vdpa_device *vdev, u8 status);
>>>> ?????? int (*reset)(struct vdpa_device *vdev);
>>>> +???? int (*stop)(struct vdpa_device *vdev, bool stop);
>>>> ?????? size_t (*get_config_size)(struct vdpa_device *vdev);
>>>> ?????? void (*get_config)(struct vdpa_device *vdev, unsigned
int
>>>> offset,
>>>> ????????????????????????? void *buf, unsigned int len);
>