Re: [PATCH bpf-next v5 1/9] libbpf: Implement changes needed for BTFGen in bpftool

["Mauricio Vásquez Bernal" <mauricio@kinvolk.io>]

On Wed, Feb 2, 2022 at 1:54 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Jan 28, 2022 at 2:33 PM Mauricio Vásquez <mauricio@kinvolk.io> wrote:
> >
> > This commit extends libbpf with the features that are needed to
> > implement BTFGen:
> >
> > - Implement bpf_core_create_cand_cache() and bpf_core_free_cand_cache()
> > to handle candidates cache.
> > - Expose bpf_core_add_cands() and bpf_core_free_cands to handle
> > candidates list.
> > - Expose bpf_core_calc_relo_insn() to bpftool.
> >
> > Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
> > Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
> > Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
> > Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
> > ---
> >  tools/lib/bpf/libbpf.c          | 44 ++++++++++++++++++++++-----------
> >  tools/lib/bpf/libbpf_internal.h | 12 +++++++++
> >  2 files changed, 41 insertions(+), 15 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 12771f71a6e7..61384d219e28 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -5195,18 +5195,18 @@ size_t bpf_core_essential_name_len(const char *name)
> >         return n;
> >  }
> >
> > -static void bpf_core_free_cands(struct bpf_core_cand_list *cands)
> > +void bpf_core_free_cands(struct bpf_core_cand_list *cands)
> >  {
> >         free(cands->cands);
> >         free(cands);
> >  }
> >
> > -static int bpf_core_add_cands(struct bpf_core_cand *local_cand,
> > -                             size_t local_essent_len,
> > -                             const struct btf *targ_btf,
> > -                             const char *targ_btf_name,
> > -                             int targ_start_id,
> > -                             struct bpf_core_cand_list *cands)
> > +int bpf_core_add_cands(struct bpf_core_cand *local_cand,
> > +                      size_t local_essent_len,
> > +                      const struct btf *targ_btf,
> > +                      const char *targ_btf_name,
> > +                      int targ_start_id,
> > +                      struct bpf_core_cand_list *cands)
> >  {
> >         struct bpf_core_cand *new_cands, *cand;
> >         const struct btf_type *t, *local_t;
> > @@ -5577,6 +5577,25 @@ static int bpf_core_resolve_relo(struct bpf_program *prog,
> >                                        targ_res);
> >  }
> >
> > +struct hashmap *bpf_core_create_cand_cache(void)
> > +{
> > +       return hashmap__new(bpf_core_hash_fn, bpf_core_equal_fn, NULL);
> > +}
> > +
> > +void bpf_core_free_cand_cache(struct hashmap *cand_cache)
> > +{
> > +       struct hashmap_entry *entry;
> > +       int i;
> > +
> > +       if (IS_ERR_OR_NULL(cand_cache))
> > +               return;
> > +
> > +       hashmap__for_each_entry(cand_cache, entry, i) {
> > +               bpf_core_free_cands(entry->value);
> > +       }
> > +       hashmap__free(cand_cache);
> > +}
> > +
> >  static int
> >  bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
> >  {
> > @@ -5584,7 +5603,6 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
> >         struct bpf_core_relo_res targ_res;
> >         const struct bpf_core_relo *rec;
> >         const struct btf_ext_info *seg;
> > -       struct hashmap_entry *entry;
> >         struct hashmap *cand_cache = NULL;
> >         struct bpf_program *prog;
> >         struct bpf_insn *insn;
> > @@ -5603,7 +5621,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
> >                 }
> >         }
> >
> > -       cand_cache = hashmap__new(bpf_core_hash_fn, bpf_core_equal_fn, NULL);
> > +       cand_cache = bpf_core_create_cand_cache();
> >         if (IS_ERR(cand_cache)) {
> >                 err = PTR_ERR(cand_cache);
> >                 goto out;
> > @@ -5694,12 +5712,8 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
> >         btf__free(obj->btf_vmlinux_override);
> >         obj->btf_vmlinux_override = NULL;
> >
> > -       if (!IS_ERR_OR_NULL(cand_cache)) {
> > -               hashmap__for_each_entry(cand_cache, entry, i) {
> > -                       bpf_core_free_cands(entry->value);
> > -               }
> > -               hashmap__free(cand_cache);
> > -       }
> > +       bpf_core_free_cand_cache(cand_cache);
> > +
> >         return err;
> >  }
> >
> > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> > index bc86b82e90d1..686a5654262b 100644
> > --- a/tools/lib/bpf/libbpf_internal.h
> > +++ b/tools/lib/bpf/libbpf_internal.h
> > @@ -529,4 +529,16 @@ static inline int ensure_good_fd(int fd)
> >         return fd;
> >  }
> >
> > +struct hashmap;
> > +
> > +struct hashmap *bpf_core_create_cand_cache(void);
> > +void bpf_core_free_cand_cache(struct hashmap *cand_cache);
>
> looking at patch #5, there is nothing special about this cand_cache,
> it's just a hashmap from u32 to some pointer. There is no need for
> libbpf to expose it to bpftool, you already have hashmap itself and
> also btfgen_hash_fn and equality callback, just do the same thing as
> you do with btfgen_info->types hashmap.
>

I'll drop them and handle the hashmap directly from bpftool.