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

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Message-ID: <20191127224753.GA1209@krava>
Date:   Wed, 27 Nov 2019 23:47:53 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        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>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.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 10:22:31PM +0100, Daniel Borkmann wrote:
> On 11/27/19 9:24 PM, Andrii Nakryiko wrote:
> > On Wed, Nov 27, 2019 at 8:38 AM Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > > 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.
> > > 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.
> 
> +1, and would also be out of scope from a BPF library point of view.

ok, static it is.. ;-) thanks for the feedback,

jirka


> 
> > I second that. I'm currently working on adding few more APIs that I'd
> > like to keep unstable for a while, until we have enough real-world
> > usage (and feedback) accumulated, before we stabilize them. With
> > LIBBPF_API and a promise of stable API, we are going to over-stress
> > and over-design APIs, potentially making them either too generic and
> > bloated, or too limited (and thus become deprecated almost at
> > inception time). I'd like to take that pressure off for a super-new
> > and in flux APIs and not hamper the progress.
> > 
> > I'm thinking of splitting off those non-stable, sort-of-internal APIs
> > into separate libbpf-experimental.h (or whatever name makes sense),
> > and let those be used only by tools like bpftool, which are only ever
> > statically link against libbpf and are ok with occasional changes to
> > those APIs (which we'll obviously fix in bpftool as well). Pahole
> > seems like another candidate that fits this bill and we might expose
> > some stuff early on to it, if it provides tangible benefits (e.g., BTF
> > dedup speeds ups, etc).
> > 
> > Then as APIs mature, we might decide to move them into libbpf.h with
> > LIBBPF_API slapped onto them. Any objections?
> 
> I don't think adding yet another libbpf_experimental.h makes sense, it feels
> too much of an invitation to add all sort of random stuff in there. We already
> do have libbpf.h and libbpf_internal.h, so everything that does not relate to
> the /stable and public/ API should be moved from libbpf.h into libbpf_internal.h
> such as the netlink helpers, as one example, and bpftool can use these since
> in-tree changes also cover the latter just fine. So overall, same page, just
> reuse/improve libbpf_internal.h instead of a new libbpf_experimental.h.
> 
> Thanks,
> Daniel
>