linux-kernel - Re: [RFC PATCH v4 1/7] libbpf: Extract BTF type remapping logic into helper function

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Message-ID: <CAEf4BzanAmmSe84GnvWSR_KLFVmeEvrxVVJAvApFNRjgeRXk8Q@mail.gmail.com>
Date: Tue, 4 Nov 2025 16:57:34 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Donglin Peng <dolinux.peng@...il.com>, ast@...nel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, Alan Maguire <alan.maguire@...cle.com>, Song Liu <song@...nel.org>, 
	pengdonglin <pengdonglin@...omi.com>
Subject: Re: [RFC PATCH v4 1/7] libbpf: Extract BTF type remapping logic into
 helper function

On Tue, Nov 4, 2025 at 4:36 PM Eduard Zingerman <eddyz87@...il.com> wrote:
>
> On Tue, 2025-11-04 at 16:11 -0800, Andrii Nakryiko wrote:
>
> [...]
>
> > > @@ -3400,6 +3400,37 @@ int btf_ext__set_endianness(struct btf_ext *btf_ext, enum btf_endianness endian)
> > >         return 0;
> > >  }
> > >
> > > +static int btf_remap_types(struct btf *btf, struct btf_ext *btf_ext,
> > > +                          btf_remap_type_fn visit, void *ctx)
> >
> > tbh, my goal is to reduce the amount of callback usage within libbpf,
> > not add more of it...
> >
> > I don't like this refactoring. We should convert
> > btf_ext_visit_type_ids() into iterators, have btf_field_iter_init +
> > btf_field_iter_next usable in for_each() form, and not try to reuse 5
> > lines of code. See my comments in the next patch.
>
> Remapping types is a concept.
> I hate duplicating code for concepts.
> Similarly, having patch #3 == patch #5 and patch #4 == patch #6 is
> plain ugly. Just waiting for a bug because we changed the one but
> forgot to change another in a year or two.

Tricky and evolving part (iterating all type ID fields) is abstracted
behind the iterator (and we should do the same for btf_ext). Iterating
types is not something tricky or requiring constant maintenance.

Same for binary search, I don't see why we'd need to adjust it. So no,
I don't want to share code between kernel and libbpf just to reuse
binary search implementation, sorry.

>
> [...]