Re: [PATCH v5 2/4] vduse: Temporarily disable control queue features

[Jason Wang <jasowang@redhat.com>]

On Mon, Dec 18, 2023 at 5:21 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
>
>
> On 12/18/23 03:50, Jason Wang wrote:
> > On Wed, Dec 13, 2023 at 7:23 PM Maxime Coquelin
> > <maxime.coquelin@redhat.com> wrote:
> >>
> >> Hi Jason,
> >>
> >> On 12/13/23 05:52, Jason Wang wrote:
> >>> On Tue, Dec 12, 2023 at 9:17 PM Maxime Coquelin
> >>> <maxime.coquelin@redhat.com> wrote:
> >>>>
> >>>> Virtio-net driver control queue implementation is not safe
> >>>> when used with VDUSE. If the VDUSE application does not
> >>>> reply to control queue messages, it currently ends up
> >>>> hanging the kernel thread sending this command.
> >>>>
> >>>> Some work is on-going to make the control queue
> >>>> implementation robust with VDUSE. Until it is completed,
> >>>> let's disable control virtqueue and features that depend on
> >>>> it.
> >>>>
> >>>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >>>
> >>> I wonder if it's better to fail instead of a mask as a start.
> >>
> >> I think it is better to use a mask and not fail, so that we can in the
> >> future use a recent VDUSE application with an older kernel.
> >
> > It may confuse the userspace unless userspace can do post check after
> > CREATE_DEV.
> >
> > And for blk we fail when WCE is set in feature_is_valid():
> >
> > static bool features_is_valid(u64 features)
> > {
> >          if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
> >                  return false;
> >
> >          /* Now we only support read-only configuration space */
> >          if (features & (1ULL << VIRTIO_BLK_F_CONFIG_WCE))
> >                  return false;
> >
> >          return true;
> > }
>
> Ok, consistency with other devices types is indeed better.
>
> But should I fail if any of the feature advertised by the application is
> not listed by the VDUSE driver, or just fail if control queue is being
> advertised by the application?

Maybe it's better to fail for any other of the features that depend on
the control vq.

Thanks

>
> Thanks,
> Maxime
>
> > Thanks
> >
> >>
> >> Why would it be better to fail than negotiating?
> >>
> >> Thanks,
> >> Maxime
> >>
> >
>