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

[Quentin Monnet <qmo@kernel.org>]

2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
<harshit.m.mogalapalli@oracle.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@oracle.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.


> +		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!

With the line break removed:

Reviewed-by: Quentin Monnet <qmo@kernel.org>