netdev - Re: [PATCH bpf-next v4 2/8] libbpf: Implement changes needed for BTFGen in bpftool

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Message-ID: <CAEf4BzaKakFkth+3ONF77VkEgTVgqS-Y=cUo03Drty1iVe7TPQ@mail.gmail.com>
Date:   Fri, 14 Jan 2022 18:04:54 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Mauricio Vásquez <mauricio@...volk.io>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v4 2/8] libbpf: Implement changes needed for
 BTFGen in bpftool

On Wed, Jan 12, 2022 at 6:27 AM Mauricio Vásquez <mauricio@...volk.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@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
>  tools/lib/bpf/Makefile          |  2 +-
>  tools/lib/bpf/libbpf.c          | 43 +++++++++++++++++++++------------
>  tools/lib/bpf/libbpf_internal.h | 12 +++++++++
>  3 files changed, 41 insertions(+), 16 deletions(-)
>
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index f947b61b2107..dba019ee2832 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -239,7 +239,7 @@ install_lib: all_cmd
>
>  SRC_HDRS := bpf.h libbpf.h btf.h libbpf_common.h libbpf_legacy.h xsk.h      \
>             bpf_helpers.h bpf_tracing.h bpf_endian.h bpf_core_read.h         \
> -           skel_internal.h libbpf_version.h
> +           skel_internal.h libbpf_version.h relo_core.h libbpf_internal.h

this is the list of public API headers, this is not the right place,
as Quentin pointed out

>  GEN_HDRS := $(BPF_GENERATED)
>
>  INSTALL_PFX := $(DESTDIR)$(prefix)/include/bpf
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 4959c03a46f4..344b8b8e8a50 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -5185,18 +5185,18 @@ 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;
> @@ -5567,6 +5567,24 @@ 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)) {

with separate function for clean up, it's nicer to invert the if
condition and exit early to reduce nesting


> +               hashmap__for_each_entry(cand_cache, entry, i) {
> +                       bpf_core_free_cands(entry->value);
> +               }
> +               hashmap__free(cand_cache);
> +       }
> +}
> +

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