Virtualization - Jun 2021 - [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

? 2021/6/24 ??5:16, Yongji Xie ??:
> On Thu, Jun 24, 2021 at 4:14 PM Jason Wang <jasowang at redhat.com>
wrote:
>>
>> ? 2021/6/24 ??12:46, Yongji Xie ??:
>>>> So we need to deal with both FEATURES_OK and reset, but
probably not
>>>> DRIVER_OK.
>>>>
>>> OK, I see. Thanks for the explanation. One more question is how
about
>>> clearing the corresponding status bit in get_status() rather than
>>> making set_status() fail. Since the spec recommends this way for
>>> validation which is done in virtio_dev_remove() and
>>> virtio_finalize_features().
>>>
>>> Thanks,
>>> Yongji
>>>
>> I think you can. Or it would be even better that we just don't set
the
>> bit during set_status().
>>
> Yes, that's what I mean.
>
>> I just realize that in vdpa_reset() we had:
>>
>> static inline void vdpa_reset(struct vdpa_device *vdev)
>> {
>>           const struct vdpa_config_ops *ops = vdev->config;
>>
>>           vdev->features_valid = false;
>>           ops->set_status(vdev, 0);
>> }
>>
>> We probably need to add the synchronization here. E.g re-read with a
>> timeout.
>>
> Looks like the timeout is already in set_status().

Do you mean the VDUSE's implementation?

>   Do we really need a
> duplicated one here?

1) this is the timeout at the vDPA layer instead of the VDUSE layer.
2) it really depends on what's the meaning of the timeout for set_status 
of VDUSE.

Do we want:

2a) for set_status(): relay the message to userspace and wait for the 
userspace to quiescence the datapath

or

2b) for set_status(): simply relay the message to userspace, reply is no 
needed. Userspace will use a command to update the status when the 
datapath is stop. The the status could be fetched via get_stats().

2b looks more spec complaint.
> And how to handle failure? Adding a return value
> to virtio_config_ops->reset() and passing the error to the upper
> layer?

Something like this.

Thanks

>
> Thanks,
> Yongji
>