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

Jason Gunthorpe
2022-11-23T18:26:13Z

On Wed, Nov 23, 2022 at 07:10:49PM +0100, Greg Kroah-Hartman wrote:
> 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:
> > > #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...

The errors in some cases are very verbose, but it is somewhat
understandable - the worst is when _Generic fails to match anything,
but also at least clang partially expanded container_of and it throws
other assertions too.

I also wonder if this could just be rolled into the normal
container_of.

in_type would have to be derived like:

in_type = typeof((out_type *)NULL)->out_member)

But I don't know if you can use typeof in a generic type matching expression..

Jason