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Date:   Wed, 23 Nov 2022 17:49:36 +0000
From:   Matthew Wilcox <willy@infradead.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 01:29:56PM -0400, Jason Gunthorpe wrote:
> #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)) \
> 		  )

There's a neat trick I found in seqlock.h:

#define generic_container_of(in_t, in, out_t, m)			\
	_Generic(*(in),							\
		const in_t: ((const out_t *)container_of(in, out_t, m)), \
		in_t: ((out_t *)container_of(in, out_type, m))	\
	)

and now it fits in 80 columns ;-)

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