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

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Message-ID: <20191204182727.GA29780@localhost.localdomain>
Date:   Wed, 4 Dec 2019 19:27:27 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        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>,
        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

On Wed, Dec 04, 2019 at 09:39:59AM -0800, Alexei Starovoitov wrote:
> On Wed, Dec 4, 2019 at 2:58 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> > 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...
> 
> Awesome. Let's figure out the logistics.
> Should we do:
> git mv tools/bpf/bpftool/ tools/lib/bpf/
> and appropriate adjustment to Makefiles ?
> or keep it where it is and only add to
> https://github.com/libbpf/libbpf/blob/master/scripts/sync-kernel.sh ?

I'd be in preference of the latter aka keeping where it is.

Thanks,
Daniel