Re: [PATCH v1 04/19] cxl: Add Get Supported Features command for kernel usage

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jan 23, 2025 at 04:30:17PM -0800, Dan Williams wrote:

> > +struct cxl_feat_entry *
> > +cxl_get_supported_feature_entry(struct cxl_features *features,
> > +				const uuid_t *feat_uuid)
> > +{
> > +	struct cxl_feat_entry *feat_entry;
> > +	struct cxl_features_state *cfs;
> > +	int count;
> > +
> > +	cfs = dev_get_drvdata(&features->dev);
> > +	if (!cfs)
> > +		return ERR_PTR(-EOPNOTSUPP);
> 
> How could this function be called outside of the driver being enabled?

+1

I hate these "defensive" checks. Either your API is always called
under a properly bound driver, or your caller is horribly wrongly
locked and the above does nothing but hide bugs.

defensive "can't happen" assertions should be marked with WARN_ON(),
but I wouldn't use that here - the oops on NULL backtrace is
sufficiently clear. :)

Jason