Re: [PATCH bpf-next v10 04/13] libbpf: Optimize type lookup with binary search for sorted BTF

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2025-12-18 at 15:29 -0800, Andrii Nakryiko wrote:

[...]

> >  static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
> >                                    const char *type_name, __u32 kind)
> 
> kind is defined as u32 but you expect caller to pass -1 to ignore the
> kind. Use int here.
> 
> >  {
> > -       __u32 i, nr_types = btf__type_cnt(btf);
> > +       const struct btf_type *t;
> > +       const char *tname;
> > +       __s32 idx;
> > +
> > +       if (start_id < btf->start_id) {
> > +               idx = btf_find_by_name_kind(btf->base_btf, start_id,
> > +                                           type_name, kind);
> > +               if (idx >= 0)
> > +                       return idx;
> > +               start_id = btf->start_id;
> > +       }
> > 
> > -       if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
> > +       if (kind == BTF_KIND_UNKN || strcmp(type_name, "void") == 0)
> >                 return 0;
> > 
> > -       for (i = start_id; i < nr_types; i++) {
> > -               const struct btf_type *t = btf__type_by_id(btf, i);
> > -               const char *name;
> > +       if (btf->sorted_start_id > 0 && type_name[0]) {
> > +               __s32 end_id = btf__type_cnt(btf) - 1;
> > +
> > +               /* skip anonymous types */
> > +               start_id = max(start_id, btf->sorted_start_id);
> 
> can sorted_start_id ever be smaller than start_id?

sorted_start_id can be zero, at two callsites for this function
start_id is passed as btf->start_id and 1.

> 
> > +               idx = btf_find_by_name_bsearch(btf, type_name, start_id, end_id);
> 
> is there ever a time when btf_find_by_name_bsearch() will work with
> different start_id and end_id? why is this not done inside the
> btf_find_by_name_bsearch()?
> 

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