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

Leo Yan
2022-12-21T03:55:38Z

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

> 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.