Re: [PATCH v3 08/16] libqos: implement VIRTIO 1.0 FEATURES_OK step

[Stefan Hajnoczi]

On Mon, Oct 21, 2019 at 02:23:15PM +0200, Thomas Huth wrote:
> On 19/10/2019 08.38, Stefan Hajnoczi wrote:
> > Device initialization has an extra step in VIRTIO 1.0.  The FEATURES_OK
> > status bit is set to indicate that feature negotiation has completed.
> > The driver then reads the status register again to check that the device
> > agrees with the final features.
> > 
> > Implement this step as part of qvirtio_set_features() instead of
> > introducing a separate function.  This way all existing code works
> > without modifications.
> > 
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> >  tests/libqos/virtio.c | 20 +++++++++++++++++---
> >  1 file changed, 17 insertions(+), 3 deletions(-)
> [...]
> > @@ -88,9 +101,10 @@ void qvirtio_set_driver(QVirtioDevice *d)
> >  
> >  void qvirtio_set_driver_ok(QVirtioDevice *d)
> >  {
> > -    d->bus->set_status(d, d->bus->get_status(d) | 
> > VIRTIO_CONFIG_S_DRIVER_OK);
> > -    g_assert_cmphex(d->bus->get_status(d), ==, VIRTIO_CONFIG_S_DRIVER_OK |
> > -                    VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_ACKNOWLEDGE);
> > +    uint8_t status = d->bus->get_status(d) | VIRTIO_CONFIG_S_DRIVER_OK;
> > +
> > +    d->bus->set_status(d, status);
> > +    g_assert_cmphex(d->bus->get_status(d), ==, status);
> >  }
> 
> The changes to qvirtio_set_driver_ok() are not mentioned in the patch
> description. Please either mention them there, or move this to a
> separate patch.

Will fix in v4.

We can no longer hardcode the status register value for DRIVER_OK since
it now depends on whether VIRTIO 1.0 is used or not.

Here is an alternative that is smaller and makes the VIRTIO 1.0
dependency obvious:

  -    g_assert_cmphex(d->bus->get_status(d), ==, VIRTIO_CONFIG_S_DRIVER_OK |
  -                    VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_ACKNOWLEDGE);
  +    g_assert_cmphex(d->bus->get_status(d), ==, VIRTIO_CONFIG_S_DRIVER_OK |
  +                    VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_ACKNOWLEDGE |
  +                    (d->features & (1ull << VIRTIO_F_VERSION_1) ?
  +                     VIRTIO_CONFIG_S_FEATURES_OK : 0));

Stefan

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