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