Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a const *

Jason Gunthorpe
2022-11-23T17:30:30Z

On Wed, Nov 23, 2022 at 06:01:47PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 23, 2022 at 12:25:32PM -0400, Jason Gunthorpe wrote:
> > On Wed, Nov 23, 2022 at 04:37:59PM +0100, Greg Kroah-Hartman wrote:
> > > static inline struct device *__kobj_to_dev(struct kobject *kobj)
> > > {
> > > return container_of(kobj, struct device, kobj);
> > > }
> > >
> > > static inline const struct device *__kobj_to_dev_const(const struct kobject *kobj)
> > > {
> > > return container_of(kobj, const struct device, kobj);
> > > }
> > >
> > > /*
> > > * container_of() will happily take a const * and spit back a non-const * as it
> > > * is just doing pointer math. But we want to be a bit more careful in the
> > > * driver code, so manually force any const * of a kobject to also be a const *
> > > * to a device.
> > > */
> > > #define kobj_to_dev(kobj) \
> > > _Generic((kobj), \
> > > const struct kobject *: __kobj_to_dev_const, \
> > > struct kobject *: __kobj_to_dev)(kobj)
> > >
> > >
> > > Want me to do the same thing here as well?
> >
> > It would be nice to have a shared macro code gen all of the above
> > instead of copy and pasting it. Then maybe other cases beyond struct
> > device could adopt const too..
>
> I think I tried to create such a beast, but failed, so ended up
> open-coding it in a few places in the USB headers already. I can try it
> again, but the redirection gets tricky (defines creating defines...)

This seems OK:

#define generic_container_of(in_type, in, out_type, out_member) \
_Generic(in, \
const in_type *: ((const out_type *)container_of(in, out_type, out_member)), \
in_type *: ((out_type *)container_of(in, out_type, out_member)) \
)

#define kobj_to_dev(__kobj) \
generic_container_of(struct kobject, __kobj, struct device, kobj)

Jason