Re: [PATCH v2 04/23] counter: Provide a wrapper to access device private data

[Lars-Peter Clausen]

On 12/27/21 12:02 PM, Greg Kroah-Hartman wrote:
> On Mon, Dec 27, 2021 at 10:45:07AM +0100, Uwe Kleine-König wrote:
> > For now this just wraps accessing struct counter_device::priv. However
> > this is about to change and converting drivers to this helper
> > individually makes fixing device lifetime issues result in easier to
> > review patches.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > ---
> >   drivers/counter/counter-core.c | 12 ++++++++++++
> >   include/linux/counter.h        |  2 ++
> >   2 files changed, 14 insertions(+)
> >
> > diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> > index f053a43c6c04..00c41f28c101 100644
> > --- a/drivers/counter/counter-core.c
> > +++ b/drivers/counter/counter-core.c
> > @@ -45,6 +45,18 @@ static struct bus_type counter_bus_type = {
> >   
> >   static dev_t counter_devt;
> >   
> > +/**
> > + * counter_priv - access counter device private data
> > + * @counter: counter device
> > + *
> > + * Get the counter device private data
> > + */
> > +void *counter_priv(const struct counter_device *const counter)
> > +{
> > +	return counter->priv;
> > +}
> > +EXPORT_SYMBOL_GPL(counter_priv);
> Shouldn't this be usin gdev_get_drvdata() and using the private data
> pointer that is already on the struct device structure itself?  The void
> *priv; should be dropped from struct counter_device entirely.
>
> Oh ick, I just now looked at 'struct counter_device', there are other
> reference counting issues in there (hint, struct cdev has a reference
> count...)  But that's independent of this patch series...
This is not a problem. The struct cdev holds a reference to the struct 
dev. This allows them to use the same allocation. As long as there is a 
reference to the cdev there will be a reference to the dev and the 
memory will be kept alive.