netdev - Re: [PATCH 0/3] perf/bpftool: Allow to link libbpf dynamically

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Message-ID: <87o8wwwery.fsf@toke.dk>
Date:   Thu, 28 Nov 2019 10:06:57 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Michael Petlan <mpetlan@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH 0/3] perf/bpftool: Allow to link libbpf dynamically

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> On Wed, Nov 27, 2019 at 1:48 AM Jiri Olsa <jolsa@...nel.org> wrote:
>>
>> hi,
>> adding support to link bpftool with libbpf dynamically,
>> and config change for perf.
>>
>> It's now possible to use:
>>   $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1
>>
>> which will detect libbpf devel package with needed version,
>> and if found, link it with bpftool.
>>
>> It's possible to use arbitrary installed libbpf:
>>   $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1 LIBBPF_DIR=/tmp/libbpf/
>>
>> I based this change on top of Arnaldo's perf/core, because
>> it contains libbpf feature detection code as dependency.
>> It's now also synced with latest bpf-next, so Toke's change
>> applies correctly.
>
> I don't like it.
> Especially Toke's patch to expose netlink as public and stable libbpf
> api.

Figured you might say that :)

> bpftools needs to stay tightly coupled with libbpf (and statically
> linked for that reason).
> Otherwise libbpf will grow a ton of public api that would have to be stable
> and will quickly become a burden.

I can see why you don't want to expose the "internal" functions as
LIBBPF_API. Doesn't *have* to mean we can't link bpftool dynamically
against the .so version of libbpf, though; will see if I can figure out
a clean way to do that...

-Toke