Hi


2022. november 23., szerda 20:06 keltezéssel, Greg Kroah-Hartman írta:

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

quoted

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

quoted

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

quoted

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...

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...

quoted

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...

I am sorry I haven't followed the previous discussion,
but has something like the following been considered?

  #define container_of2(ptr, type, member) \
  	_Generic((ptr), \
  		typeof_member(const type, member) *: container_of((ptr), const type, member), \
  		const void *: container_of((ptr), const type, member), \
  		default: container_of((ptr), type, member) \
  	)

This is not perfect by any means, but I believe it is a reasonable
improvement. It only really works reliably if the member type and
the specified `type` in the arguments are unqualified,
but I believe that should cover the majority of cases.

I have tried to build an x86-64 defconfig with this and there are
numerous const violations, but I haven't seen any false positives.

[...]

Regards,
Barnabás Pőcze