netdev - Re: [PATCH bpf-next 1/4] bpftool: Print the enum's name instead of value

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Date:   Tue, 17 Mar 2020 13:03:46 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/4] bpftool: Print the enum's name instead of value

On Sun, Mar 15, 2020 at 5:56 PM Martin KaFai Lau <kafai@...com> wrote:
>
> This patch prints the enum's name if there is one found in
> the array of btf_enum.
>
> The commit 9eea98497951 ("bpf: fix BTF verification of enums")
> has details about an enum could have any power-of-2 size (up to 8 bytes).
> This patch also takes this chance to accommodate these non 4 byte
> enums.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
>  tools/bpf/bpftool/btf_dumper.c | 35 +++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
> index 01cc52b834fa..57bd6c0fafc9 100644
> --- a/tools/bpf/bpftool/btf_dumper.c
> +++ b/tools/bpf/bpftool/btf_dumper.c
> @@ -43,9 +43,38 @@ static int btf_dumper_modifier(const struct btf_dumper *d, __u32 type_id,
>         return btf_dumper_do_type(d, actual_type_id, bit_offset, data);
>  }
>
> -static void btf_dumper_enum(const void *data, json_writer_t *jw)
> +static void btf_dumper_enum(const struct btf_dumper *d,
> +                           const struct btf_type *t,
> +                           const void *data)
>  {
> -       jsonw_printf(jw, "%d", *(int *)data);
> +       const struct btf_enum *enums = btf_enum(t);
> +       __s64 value;
> +       __u16 i;
> +
> +       switch (t->size) {
> +       case 8:
> +               value = *(__s64 *)data;
> +               break;
> +       case 4:
> +               value = *(__s32 *)data;
> +               break;
> +       case 2:
> +               value = *(__s16 *)data;
> +               break;
> +       default:
> +               value = *(__s8 *)data;
> +       }

I'm scared of catch-all defaults like this. Let's do `case 1: `
explicitly and error out on anything else here?

> +
> +       for (i = 0; i < btf_vlen(t); i++) {
> +               if (value == enums[i].val) {
> +                       jsonw_string(d->jw,
> +                                    btf__name_by_offset(d->btf,
> +                                                        enums[i].name_off));
> +                       return;
> +               }
> +       }
> +
> +       jsonw_int(d->jw, value);
>  }
>
>  static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,
> @@ -366,7 +395,7 @@ static int btf_dumper_do_type(const struct btf_dumper *d, __u32 type_id,
>         case BTF_KIND_ARRAY:
>                 return btf_dumper_array(d, type_id, data);
>         case BTF_KIND_ENUM:
> -               btf_dumper_enum(data, d->jw);
> +               btf_dumper_enum(d, t, data);
>                 return 0;
>         case BTF_KIND_PTR:
>                 btf_dumper_ptr(data, d->jw, d->is_plain_text);
> --
> 2.17.1
>