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

Andrii Nakryiko
2022-12-22T18:52:19Z

On Tue, Dec 20, 2022 at 7:55 PM Leo Yan <leo.yan@linaro.org> 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?

-ENODATA sounds good to me, yep.

>
> Thanks,
> Leo
>
> > In general, I always found these strerror() messages extremely
> > unhelpful and confusing. I wonder if we should make an effort to
> > actually emit symbolic names of errors instead (literally, "-ENOENT"
> > in this case). This is all tooling for engineers, I find -ENOENT or
> > -ESRCH much more meaningful as an error message, compared to "No such
> > file" seemingly human-readable interpretation.
> >
> > Quenting, what do you think about the above proposal for bpftool? We
> > can have some libbpf helper internally and do it in libbpf error
> > messages as well and just reuse the logic in bpftool, perhaps?
> >
> > Anyways, I've applied this patch set to bpf-next. Thanks.