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Date:   Wed, 23 Nov 2022 18:01:47 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Jason Gunthorpe <jgg@ziepe.ca>
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Subject: Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a
 const *
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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...)

thanks,

greg k-h