Subject: Re: [PATCH 1/2] virtio: allow drivers to validate features

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 30 Mar 2017 17:57:11 +0300

On Thu, Mar 30, 2017 at 11:06:27AM +0200, Cornelia Huck wrote:
> On Wed, 29 Mar 2017 20:14:44 +0300
> "Michael S. Tsirkin" <[email-masked]> wrote:
> 
> > Some drivers can't support all features in all configurations.  At the
> > moment we blindly set FEATURES_OK and later FAILED.  Support this better
> > by adding a callback drivers can use to do some early checks.
> 
> Looks reasonable. Do we need to document that the driver must not do
> anything beyond dealing with features and reading the config space that
> early?

It's up to the driver - we probably should document that on failure
neither probe nor remove will be called. On success we proceed
to probe.

> > 
> > Signed-off-by: Michael S. Tsirkin <[email-masked]>
> > ---
> >  drivers/virtio/virtio.c | 6 ++++++
> >  include/linux/virtio.h  | 1 +
> >  2 files changed, 7 insertions(+)
> > 
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index 400d70b..48230a5 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -232,6 +232,12 @@ static int virtio_dev_probe(struct device *_d)
> >  		if (device_features & (1ULL << i))
> >  			__virtio_set_bit(dev, i);
> >  
> > +	if (drv->validate) {
> > +		err = drv->validate(dev);
> > +		if (err)
> > +			goto err;
> > +	}
> > +
> >  	err = virtio_finalize_features(dev);
> >  	if (err)
> >  		goto err;
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index 193fea9..ed04753 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -176,6 +176,7 @@ struct virtio_driver {
> >  	unsigned int feature_table_size;
> >  	const unsigned int *feature_table_legacy;
> >  	unsigned int feature_table_size_legacy;
> > +	int (*validate)(struct virtio_device *dev);
> >  	int (*probe)(struct virtio_device *dev);
> >  	void (*scan)(struct virtio_device *dev);
> >  	void (*remove)(struct virtio_device *dev);
> 
> Would be good to add some doc; but other members are undocumented here
> already...

True. Patches welcome.