linux-kernel - Re: [PATCH v3 1/2] libbpf: show error info about missing ".BTF" section

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Date:   Fri, 30 Dec 2022 20:10:20 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Quentin Monnet <quentin@...valent.com>,
        Changbin Du <changbin.du@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 1/2] libbpf: show error info about missing ".BTF"
 section

On Wed, Dec 21, 2022 at 11:55:24AM +0800, Leo Yan wrote:
> On Tue, Dec 20, 2022 at 04:13:13PM -0800, Andrii Nakryiko wrote:
> 
> [...]
> 
> > > > > > @@ -990,6 +990,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
> > > > > >   err = 0;
> > > > > >
> > > > > >   if (!btf_data) {
> > > > > > +         pr_warn("failed to find '%s' ELF section in %s\n", BTF_ELF_SEC, path);
> > > > > >           err = -ENOENT;
> > >
> > > btf_parse_elf() returns -ENOENT when ELF file doesn't contain BTF
> > > section, therefore, bpftool dumps error string "No such file or
> > > directory".  It's confused that actually vmlinux is existed.
> > >
> > > I am wondering if we can use error -LIBBPF_ERRNO__FORMAT (or any
> > > better choice?) to replace -ENOENT at here, this can avoid bpftool to
> > > outputs "No such file or directory" in this case.
> > 
> > The only really meaningful error code would be -ESRCH, which
> > strerror() will translate to "No such process", which is also
> > completely confusing.
> 
> Or maybe -ENODATA (No data available) is a better choice?
> 
> Thanks,
> Leo
>
Yan, will you have a patch for this suggestion?

[snip]

-- 
Cheers,
Changbin Du