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

Greg Kroah-Hartman
2022-11-25T21:21:16Z

On Wed, Nov 23, 2022 at 02:25:59PM -0400, Jason Gunthorpe wrote:
> 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.

I think we might be able to now, my previous attempts with inline
functions prevented that. I'll beat on that tomorrow...

> 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..

Maybe that is what threw me before, I can't remember. I do know we
tried a number of different attempts, can't recall the failed ones...

thanks,

greg k-h