Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Feb 08, 2022 at 12:00:25AM +0800, Yinjun Zhang wrote:
> When reworking btf__get_from_id() in commit a19f93cfafdf the error
> handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> callers of btf__get_from_id(), after the rework it is. This lead to a
> change in behavior in print_key_value() that now prints an error when
> trying to lookup keys in maps with no btf available.
> 
> Fix this by following the way used in dumping maps to allow to look up
> keys in no-btf maps, by which it decides whether and where to get the
> btf info according to the btf value type.
> 
> Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> Signed-off-by: Simon Horman <simon.horman@corigine.com>

once this one gets merged, I'd send this fix on top of that:
  https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka


> ---
>  tools/bpf/bpftool/map.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index cc530a229812..4fc772d66e3a 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>  	json_writer_t *btf_wtr;
>  	struct btf *btf;
>  
> -	btf = btf__load_from_kernel_by_id(info->btf_id);
> -	if (libbpf_get_error(btf)) {
> -		p_err("failed to get btf");
> +	btf = get_map_kv_btf(info);
> +	if (libbpf_get_error(btf))
>  		return;
> -	}
>  
>  	if (json_output) {
>  		print_entry_json(info, key, value, btf);
> -- 
> 1.8.3.1
>