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

[Jason Wang]

在 2021/6/24 下午5:16, Yongji Xie 写道:
> On Thu, Jun 24, 2021 at 4:14 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > 在 2021/6/24 下午12:46, Yongji Xie 写道:
> > > > 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