netdev - Re: [PATCH 3/3] samples: bpf: refactor BPF map in map test with libbpf

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Message-ID: <CAEf4BzbGk2xSGAkLEXKSg3NhrL28o+cmW9jTq2=EhggJEYT=5Q@mail.gmail.com>
Date:   Fri, 26 Jun 2020 13:30:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH 3/3] samples: bpf: refactor BPF map in map test with libbpf

On Fri, Jun 26, 2020 at 1:18 AM Daniel T. Lee <danieltimlee@...il.com> wrote:
>
> From commit 646f02ffdd49 ("libbpf: Add BTF-defined map-in-map
> support"), a way to define internal map in BTF-defined map has been
> added.
>
> Instead of using previous 'inner_map_idx' definition, the structure to
> be used for the inner map can be directly defined using array directive.
>
>     __array(values, struct inner_map)
>
> This commit refactors map in map test program with libbpf by explicitly
> defining inner map with BTF-defined format.
>
> Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> ---

Thanks for the clean up, looks good except that prog NULL check.

It also seems like this is the last use of bpf_map_def_legacy, do you
mind removing it as well?


>  samples/bpf/Makefile               |  2 +-
>  samples/bpf/test_map_in_map_kern.c | 85 +++++++++++++++---------------
>  samples/bpf/test_map_in_map_user.c | 53 +++++++++++++++++--
>  3 files changed, 91 insertions(+), 49 deletions(-)
>

[...]

>
>         snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> +       obj = bpf_object__open_file(filename, NULL);
> +       if (libbpf_get_error(obj)) {

this is right, but...

> +               fprintf(stderr, "ERROR: opening BPF object file failed\n");
> +               return 0;
> +       }
>
> -       if (load_bpf_file(filename)) {
> -               printf("%s", bpf_log_buf);
> -               return 1;
> +       prog = bpf_object__find_program_by_name(obj, "trace_sys_connect");
> +       if (libbpf_get_error(prog)) {

this is wrong. Just NULL check. libbpf APIs are not very consistent
with what they return, unfortunately.

> +               printf("finding a prog in obj file failed\n");
> +               goto cleanup;
> +       }
> +

[...]