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 17:45:02 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.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 10/09/2020 17:42, Andrii Nakryiko wrote:
> 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.

Yes, I chose to keep the first one with no functional change to keep the
logs cleaner.

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

Thanks!
Quentin