netdev - Re: [PATCH bpf-next v3 2/3] tools: bpftool: keep errors for map-of-map dumps if distinct from ENOENT

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Date:   Thu, 10 Sep 2020 09:42:36 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 2/3] tools: bpftool: keep errors for
 map-of-map dumps if distinct from ENOENT

On Thu, Sep 10, 2020 at 3:27 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> When dumping outer maps or prog_array maps, and on lookup failure,
> bpftool simply skips the entry with no error message. This is because
> the kernel returns non-zero when no value is found for the provided key,
> which frequently happen for those maps if they have not been filled.
>
> When such a case occurs, errno is set to ENOENT. It seems unlikely we
> could receive other error codes at this stage (we successfully retrieved
> map info just before), but to be on the safe side, let's skip the entry
> only if errno was ENOENT, and not for the other errors.
>
> v3: New patch
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  tools/bpf/bpftool/map.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index c8159cb4fb1e..d8581d5e98a1 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -240,8 +240,8 @@ print_entry_error(struct bpf_map_info *map_info, void *key, int lookup_errno)
>          * means there is no entry for that key. Do not print an error message
>          * in that case.
>          */
> -       if (map_is_map_of_maps(map_info->type) ||
> -           map_is_map_of_progs(map_info->type))
> +       if ((map_is_map_of_maps(map_info->type) ||
> +            map_is_map_of_progs(map_info->type)) && lookup_errno == ENOENT)
>                 return;


Ah, ok, you decided to split it out into a separate patch. Ok.

Acked-by: Andrii Nakryiko <andriin@...com>

>
>         if (json_output) {
> --
> 2.25.1
>