Re: [PATCH bpf-next v9 01/10] libbpf: Add BTF permutation support for type reordering

[Donglin Peng]

On Wed, Dec 17, 2025 at 6:00 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> On Mon, 2025-12-08 at 14:23 +0800, Donglin Peng wrote:
> > From: pengdonglin <pengdonglin@xxxxxxxxxx>
> >
> > Introduce btf__permute() API to allow in-place rearrangement of BTF types.
> > This function reorganizes BTF type order according to a provided array of
> > type IDs, updating all type references to maintain consistency.
> >
> > Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> > Cc: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > Cc: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
> > Cc: Xiaoqin Zhang <zhangxiaoqin@xxxxxxxxxx>
> > Signed-off-by: pengdonglin <pengdonglin@xxxxxxxxxx>
> > ---
>
> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
>
> [...]
>
> > diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> > index cc01494d6210..ba67e5457e3a 100644
> > --- a/tools/lib/bpf/btf.h
> > +++ b/tools/lib/bpf/btf.h
> > @@ -281,6 +281,42 @@ LIBBPF_API int btf__dedup(struct btf *btf, const struct btf_dedup_opts *opts);
> >   */
> >  LIBBPF_API int btf__relocate(struct btf *btf, const struct btf *base_btf);
> >
> > +struct btf_permute_opts {
> > +     size_t sz;
> > +     /* optional .BTF.ext info along the main BTF info */
> > +     struct btf_ext *btf_ext;
> > +     size_t :0;
> > +};
> > +#define btf_permute_opts__last_field btf_ext
> > +
> > +/**
> > + * @brief **btf__permute()** performs in-place BTF type rearrangement
> > + * @param btf BTF object to permute
> > + * @param id_map Array mapping original type IDs to new IDs
> > + * @param id_map_cnt Number of elements in @id_map
> > + * @param opts Optional parameters for BTF extension updates
> > + * @return 0 on success, negative error code on failure
> > + *
> > + * **btf__permute()** rearranges BTF types according to the specified ID mapping.
> > + * The @id_map array defines the new type ID for each original type ID.
> > + *
> > + * For **base BTF**:
> > + * - @id_map must include all types from ID 1 to `btf__type_cnt(btf)-1`
> > + * - @id_map_cnt should be `btf__type_cnt(btf) - 1`
> > + * - Mapping uses `id_map[original_id - 1] = new_id`
> > + *
> > + * For **split BTF**:
> > + * - @id_map should cover only split types
> > + * - @id_map_cnt should be `btf__type_cnt(btf) - btf__type_cnt(btf__base_btf(btf))`
> > + * - Mapping uses `id_map[original_id - btf__type_cnt(btf__base_btf(btf))] = new_id`
>
> Nit: internally the rule does not have special cases:
>
>        id_map[original_id - start_id] = new_id
>
>      So, maybe there is no need split these cases in the docstring?
>      Otherwise it is not immediately clear that both cases are handled
>      uniformly.

Thanks, I agree and will refine the docstring.

>
> > + *
> > + * On error, returns negative error code and sets errno:
> > + *   - `-EINVAL`: Invalid parameters or ID mapping (duplicates, out-of-range)
> > + *   - `-ENOMEM`: Memory allocation failure
> > + */
> > +LIBBPF_API int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
> > +                         const struct btf_permute_opts *opts);
> > +
> >  struct btf_dump;
> >
> >  struct btf_dump_opts {
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 8ed8749907d4..b778e5a5d0a8 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -451,4 +451,5 @@ LIBBPF_1.7.0 {
> >       global:
> >               bpf_map__set_exclusive_program;
> >               bpf_map__exclusive_program;
> > +             btf__permute;
> >  } LIBBPF_1.6.0;