Re: [PATCH 2/3] bitset: fix build for GCC without experimental API

[Thomas Monjalon <thomas@monjalon.net>]

15/10/2024 14:53, Morten Brørup:
> > From: David Marchand [mailto:david.marchand@redhat.com]
> > @@ -255,7 +255,13 @@ __rte_experimental
> >  static inline bool
> >  rte_bitset_test(const uint64_t *bitset, size_t bit_num)
> >  {
> > +#ifdef ALLOW_EXPERIMENTAL_API
> >  	return __RTE_BITSET_DELEGATE(rte_bit_test, bitset, bit_num);
> > +#else
> > +	RTE_SET_USED(bitset);
> > +	RTE_SET_USED(bit_num);
> > +	return false;
> > +#endif
> >  }
> 
> This looks wrong! The API is exposed, but does nothing.

Yes, this is what we did already in the past for other experimental functions
called from inline functions.
There is no choice, the compiler is hitting the warning.

> It is possible to build without ALLOW_EXPERIMENTAL_API; the compiler will emit warnings when using experimental APIs.

Yes it is possible to build,
but it is not said it should work the same.

> If those compiler warnings are not handled as errors, the compiled application will be full of bugs.

Yes, that's why there are warnings.
We may document it better but that's the behavior we have for years.
There is no easy solution, and making experimental functions work
without defining ALLOW_EXPERIMENTAL_API is not a really interesting goal.
I think the word "allow" suggests it is not supposed to work if not allowed.

It would be more interesting to make sure the users understand
why we have this flag and how to enable it.
I propose adding some docs, and mentioning ALLOW_EXPERIMENTAL_API
in the the __rte_experimental message in rte_compat.h.