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

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Feb 07, 2022 at 09:42:25AM -0800, Andrii Nakryiko wrote:
> On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> 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>
> > ---
> >  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))
> 
> See discussion in [0], it seems relevant.
> 
>   [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

I checked and this patch does not fix the problem for me,
but looks like similar issue, do you have test case for this?

mine is to dump any no-btf map with -p option

thanks,
jirka