On Wed, Nov 23, 2022 at 05:49:36PM +0000, Matthew Wilcox wrote:

On Wed, Nov 23, 2022 at 01:29:56PM -0400, Jason Gunthorpe wrote:

quoted

#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 ;-)

Nice trick!  Dropping the inline functions is a bit different, let me
see if that still gives a sane error if we pass an incorrect type or
mess with the const * the wrong way.  I'll run some tests tomorrow
afternoon...

thanks,

greg k-h