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

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

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.


> +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);
> +void bpf_core_free_cands(struct bpf_core_cand_list *cands);
> +
>  #endif /* __LIBBPF_LIBBPF_INTERNAL_H */
> --
> 2.25.1
>