netdev - Re: [PATCH bpf-next v4 06/11] libbpf: Support kernel module function calls

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Message-ID: <20210924235417.eqhzbrajwkenk6rd@apollo.localdomain>
Date:   Sat, 25 Sep 2021 05:24:17 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 06/11] libbpf: Support kernel module function
 calls

On Wed, Sep 22, 2021 at 04:11:13AM IST, Andrii Nakryiko wrote:
> On Mon, Sep 20, 2021 at 7:15 AM Kumar Kartikeya Dwivedi
> <memxor@...il.com> wrote:
> > [...]
> > +                       return -E2BIG;
> > +               }
> > +               ext->ksym.offset = index;
>
> > +       } else {
> > +               ext->ksym.offset = 0;
> >         }
>
> I think it will be cleaner if you move the entire offset determination
> logic after all the other checks are performed and ext is mostly
> populated. That will also make the logic shorter and simpler because
> if ayou find kern_btf_fd match, you can exit early (or probably rather

Ack to everything else (including the other mail), but...

> goto to report the match and exit). Otherwise
>

This sentence got eaten up.

> >
> >         kern_func = btf__type_by_id(kern_btf, kfunc_id);
>
> this is actually extremely wasteful for module BTFs. Let's add
> internal (at least for now) helper that will search only for "own" BTF
> types in the BTF, skipping types in base BTF. Something like
> btf_type_by_id_own()?
>

Just to make sure I am not misunderstanding: I don't see where this is wasteful.
btf_type_by_id seems to not be searching anything, but just returns pointer in
base BTF if kfunc_id < btf->start_id, otherwise in module BTF.

What am I missing? I guess the 'kern_btf' name was the source of confusion? If
so, I'll rename it.

Thanks.

--
Kartikeya