linux-kernel - Re: [PATCH 10/16] virtio: add API to enable VQs early

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Date:	Mon, 6 Oct 2014 17:51:47 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 10/16] virtio: add API to enable VQs early

On Mon, Oct 06, 2014 at 04:08:16PM +0200, Cornelia Huck wrote:
> On Sun, 5 Oct 2014 19:07:19 +0300
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > virtio spec requires DRIVER_OK to be set before
> > VQs are used, but some drivers use VQs before probe
> > function returns.
> > Since DRIVER_OK is set after probe, this violates the spec.
> 
> "Even though transitional devices support this behaviour, we want to
> make it possible for those early callers to become spec compliant."
> 
> ?

Exactly.

> > 
> > Add API for drivers to call before using VQs.
> > 
> > Sets DRIVER_OK internally.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >  include/linux/virtio_config.h | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index e8f8f71..6127fc8 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -109,6 +109,23 @@ struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
> >  	return vq;
> >  }
> > 
> > +/**
> > + * virtio_early_enable_vqs - enable vq use in probe function
> > + * @vdev: the device
> > + *
> > + * Driver must call this to use vqs in the probe function.
> > + *
> > + * Note: vqs are enabled automatically after probe returns.
> > + */
> > +static inline
> > +void virtio_early_enable_vqs(struct virtio_device *dev)
> > +{
> > +	unsigned status = dev->config->get_status(dev);
> > +
> > +	BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
> > +	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> > +}
> > +
> 
> Maybe virtio_enable_vqs_early() instead?

OK.

> >  static inline
> >  const char *virtio_bus_name(struct virtio_device *vdev)
> >  {
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