linux-kernel - Re: [PATCHv4 0/6] perf/bpftool: Allow to link libbpf dynamically

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Message-ID: <877e3cpdc9.fsf@toke.dk>
Date:   Wed, 04 Dec 2019 11:57:58 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Networking <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>,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [PATCHv4 0/6] perf/bpftool: Allow to link libbpf dynamically

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

> On Mon, Dec 2, 2019 at 1:15 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Ah, that is my mistake: I was getting dynamic libbpf symbols with this
>> approach, but that was because I had the version of libbpf.so in my
>> $LIBDIR that had the patch to expose the netlink APIs as versioned
>> symbols; so it was just pulling in everything from the shared library.
>>
>> So what I was going for was exactly what you described above; but it
>> seems that doesn't actually work. Too bad, and sorry for wasting your
>> time on this :/
>
> bpftool is currently tightly coupled with libbpf and very likely
> in the future the dependency will be even tighter.
> In that sense bpftool is an extension of libbpf and libbpf is an extension
> of bpftool.
> Andrii is working on set of patches to generate user space .c code
> from bpf program.
> bpftool will be generating the code that is specific for the version
> bpftool and for
> the version of libbpf. There will be compatibility layers as usual.
> But in general the situation where a bug in libbpf is so criticial
> that bpftool needs to repackaged is imo less likely than a bug in
> bpftool that will require re-packaging of libbpf.
> bpftool is quite special. It's not a typical user of libbpf.
> The other way around is more correct. libbpf is a user of the code
> that bpftool generates and both depend on each other.
> perf on the other side is what typical user space app that uses
> libbpf will look like.
> I think keeping bpftool in the kernel while packaging libbpf
> out of github was an oversight.
> I think we need to mirror bpftool into github/libbpf as well
> and make sure they stay together. The version of libbpf == version of bpftool.
> Both should come from the same package and so on.
> May be they can be two different packages but
> upgrading one should trigger upgrade of another and vice versa.
> I think one package would be easier though.
> Thoughts?

Yup, making bpftool explicitly the "libbpf command line interface" makes
sense and would help clarify the relationship between the two. As Jiri
said, we are already moving in that direction packaging-wise...

-Toke