Re: [PATCH bpf-next 2/5] bpftool: Fix missing BTF output for json during map dump

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Martin Lau <kafai@fb.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	David Miller <davem@davemloft.net>,
	Kernel Team <Kernel-team@fb.com>,
	Networking <netdev@vger.kernel.org>,
	Paul Chaignon <paul.chaignon@orange.com>
Subject: Re: [PATCH bpf-next 2/5] bpftool: Fix missing BTF output for json during map dump
Date: Tue, 14 Jan 2020 22:36:51 -0800	[thread overview]
Message-ID: <CAEf4BzZpvt+zNxMwAUjebNCQLpwHzX_Abj=efQXghjxjL6VKzg@mail.gmail.com> (raw)
In-Reply-To: <20200115055406.gsouajufdzussm6e@kafai-mbp.dhcp.thefacebook.com>

On Tue, Jan 14, 2020 at 9:54 PM Martin Lau <kafai@fb.com> wrote:
>
> On Tue, Jan 14, 2020 at 05:34:33PM -0800, Andrii Nakryiko wrote:
> > On Tue, Jan 14, 2020 at 2:45 PM Martin KaFai Lau <kafai@fb.com> wrote:
> > >
> > > The btf availability check is only done for plain text output.
> > > It causes the whole BTF output went missing when json_output
> > > is used.
> > >
> > > This patch simplifies the logic a little by avoiding passing "int btf" to
> > > map_dump().
> > >
> > > For plain text output, the btf_wtr is only created when the map has
> > > BTF (i.e. info->btf_id != 0).  The nullness of "json_writer_t *wtr"
> > > in map_dump() alone can decide if dumping BTF output is needed.
> > > As long as wtr is not NULL, map_dump() will print out the BTF-described
> > > data whenever a map has BTF available (i.e. info->btf_id != 0)
> > > regardless of json or plain-text output.
> > >
> > > In do_dump(), the "int btf" is also renamed to "int do_plain_btf".
> > >
> > > Fixes: 99f9863a0c45 ("bpftool: Match maps by name")
> > > Cc: Paul Chaignon <paul.chaignon@orange.com>
> > > Signed-off-by: Martin KaFai Lau <kafai@fb.com>
> > > ---
> >
> > just one nit below
> >
> > Acked-by: Andrii Nakryiko <andriin@fb.com>
> >
> > >  tools/bpf/bpftool/map.c | 42 ++++++++++++++++++++---------------------
> > >  1 file changed, 20 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> > > index e00e9e19d6b7..45c1eda6512c 100644
> > > --- a/tools/bpf/bpftool/map.c
> > > +++ b/tools/bpf/bpftool/map.c
> > > @@ -933,7 +933,7 @@ static int maps_have_btf(int *fds, int nb_fds)
> > >
> > >  static int
> > >  map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
> > > -        bool enable_btf, bool show_header)
> > > +        bool show_header)
> > >  {
> > >         void *key, *value, *prev_key;
> > >         unsigned int num_elems = 0;
> > > @@ -950,18 +950,16 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
> > >
> > >         prev_key = NULL;
> > >
> > > -       if (enable_btf) {
> > > -               err = btf__get_from_id(info->btf_id, &btf);
> > > -               if (err || !btf) {
> > > -                       /* enable_btf is true only if we've already checked
> > > -                        * that all maps have BTF information.
> > > -                        */
> > > -                       p_err("failed to get btf");
> > > -                       goto exit_free;
> > > +       if (wtr) {
> > > +               if (info->btf_id) {
> >
> > combine into if (wtr && info->btf_id) and reduce nestedness?
> There is other logic under the same "if (wtr)".
> Thus, it is better to leave it as is.

My bad, missed those tiny minuses in diff :) Of course that would be incorrect.

> and this indentation will be gone in patch 5.
>
> >
> >
> > > +                       err = btf__get_from_id(info->btf_id, &btf);
> > > +                       if (err || !btf) {
> > > +                               err = err ? : -ESRCH;
> > > +                               p_err("failed to get btf");
> > > +                               goto exit_free;
> > > +                       }
> >
> > [...]