linux-kernel - Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output

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Message-ID: <e029dc37-9e83-471d-b536-b29130013d1e@oracle.com>
Date: Sun, 2 Nov 2025 00:16:22 +0530
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: Quentin Monnet <qmo@...nel.org>, bpf@...r.kernel.org
Cc: alan.maguire@...cle.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support
 JSON output

Hi Quentin,

On 01/11/25 22:29, Quentin Monnet wrote:
> 2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
> <harshit.m.mogalapalli@...cle.com>
>> It is useful to print map ID on successful creation.
>>
>> JSON case:
>> $ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 128 name map4
>> {"id":12}
>>
>> Generic case:
>> $ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 128 name map5
>> Map successfully created with ID: 15
>>
>> Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
>> ---
>>   tools/bpf/bpftool/map.c | 21 +++++++++++++++++----
>>   1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
>> index c9de44a45778..80c96b33b553 100644
>> --- a/tools/bpf/bpftool/map.c
>> +++ b/tools/bpf/bpftool/map.c
>> @@ -1251,6 +1251,8 @@ static int do_create(int argc, char **argv)
>>   	LIBBPF_OPTS(bpf_map_create_opts, attr);
>>   	enum bpf_map_type map_type = BPF_MAP_TYPE_UNSPEC;
>>   	__u32 key_size = 0, value_size = 0, max_entries = 0;
>> +	struct bpf_map_info map_info = {};
>> +	__u32 map_info_len = sizeof(map_info);
>>   	const char *map_name = NULL;
>>   	const char *pinfile;
>>   	int err = -1, fd;
>> @@ -1353,13 +1355,24 @@ static int do_create(int argc, char **argv)
>>   	}
>>   
>>   	err = do_pin_fd(fd, pinfile);
>> -	close(fd);
>>   	if (err)
>> -		goto exit;
>> +		goto close_fd;
>>   
>> -	if (json_output)
>> -		jsonw_null(json_wtr);
>> +	err = bpf_obj_get_info_by_fd(fd, &map_info, &map_info_len);
>> +	if (err) {
>> +		p_err("Failed to fetch map info: %s\n", strerror(errno));
> 
> 
> Nit: Please remove the line break ('\n') here, p_err() already adds it.
> 

Ah thanks for spotting that, will do.

> 
>> +		goto close_fd;
>> +	}
>>   
>> +	if (json_output) {
>> +		jsonw_start_object(json_wtr);
>> +		jsonw_int_field(json_wtr, "id", map_info.id);
>> +		jsonw_end_object(json_wtr);
> 
> 
> I've been wondering if we should have some parent object like
> '{"map_created": { "id": 15 }}' in case we later add more output, but I
> can't really see a good use case at the moment, I'm probably
> overthinking it... So I'm good with the current output. Thanks for this!
> 

Thanks a lot for the review.

> With the line break removed:
> 

Sure will send a next version with updates to p_err and selftest(to not 
echo messages on success)

> Reviewed-by: Quentin Monnet <qmo@...nel.org>
Regards,
Harshit