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

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Message-ID: <CAEf4BzbUK98tsYH1mSNoTjuVB4dstRsL5rpkA+9nRCcqrdn6-Q@mail.gmail.com>
Date:   Mon, 2 Dec 2019 09:09:33 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     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>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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

On Wed, Nov 27, 2019 at 1:49 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

I wonder what's the motivation behind these changes, though? Why is
linking bpftool dynamically with libbpf is necessary and important?
They are both developed tightly within kernel repo, so I fail to see
what are the huge advantages one can get from linking them
dynamically.

>
> 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.
>
> Also available in:
>   git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   libbpf/dyn
>
> thanks,
> jirka
>
>
> ---
> Jiri Olsa (2):
>       perf tools: Allow to specify libbpf install directory
>       bpftool: Allow to link libbpf dynamically
>
> Toke Høiland-Jørgensen (1):
>       libbpf: Export netlink functions used by bpftool
>
>  tools/bpf/bpftool/Makefile        | 40 +++++++++++++++++++++++++++++++++++++++-
>  tools/build/feature/test-libbpf.c |  9 +++++++++
>  tools/lib/bpf/libbpf.h            | 22 +++++++++++++---------
>  tools/lib/bpf/libbpf.map          |  7 +++++++
>  tools/lib/bpf/nlattr.h            | 15 ++++++++++-----
>  tools/perf/Makefile.config        | 27 ++++++++++++++++++++-------
>  6 files changed, 98 insertions(+), 22 deletions(-)
>