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

On Fri, Jun 25, 2021 at 11:09 AM Jason Wang [off-list ref] wrote:

在 2021/6/24 下午5:16, Yongji Xie 写道:

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On Thu, Jun 24, 2021 at 4:14 PM Jason Wang [off-list ref] wrote:

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在 2021/6/24 下午12:46, Yongji Xie 写道:

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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.

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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?

Yes.

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  Do we really need a
duplicated one here?

1) this is the timeout at the vDPA layer instead of the VDUSE layer.

OK, I get it.

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.

Looks good to me. And I think we can use the reply of the message to
update the status instead of introducing a new command.

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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.

OK.

Thanks,
Yongji