netdev - Re: [PATCH bpf-next v6 6/7] bpftool: gen min_core

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Date:   Tue, 15 Feb 2022 17:26:05 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Mauricio Vásquez Bernal <mauricio@...volk.io>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v6 6/7] bpftool: gen min_core_btf explanation and examples

On Tue, Feb 15, 2022 at 2:56 PM Mauricio Vásquez Bernal
<mauricio@...volk.io> wrote:
>
> On Fri, Feb 11, 2022 at 7:42 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Wed, Feb 9, 2022 at 2:27 PM Mauricio Vásquez <mauricio@...volk.io> wrote:
> > >
> > > From: Rafael David Tinoco <rafaeldtinoco@...il.com>
> > >
> > > Add "min_core_btf" feature explanation and one example of how to use it
> > > to bpftool-gen man page.
> > >
> > > Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> > > Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> > > Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> > > Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> > > ---
> > >  .../bpf/bpftool/Documentation/bpftool-gen.rst | 93 +++++++++++++++++++
> > >  1 file changed, 93 insertions(+)
> > >
> >
> > [...]
> >
> > > +Now, the "5.4.0-smaller.btf" file may be used by libbpf as an external BTF file
> > > +when loading the "one.bpf.o" object into the "5.4.0-example" kernel. Note that
> > > +the generated BTF file won't allow other eBPF objects to be loaded, just the
> > > +ones given to min_core_btf.
> > > +
> > > +::
> > > +
> > > +  struct bpf_object *obj = NULL;
> > > +  struct bpf_object_open_opts openopts = {};
> > > +
> > > +  openopts.sz = sizeof(struct bpf_object_open_opts);
> > > +  openopts.btf_custom_path = "./5.4.0-smaller.btf";
> > > +
> > > +  obj = bpf_object__open_file("./one.bpf.o", &openopts);
> >
> > Can you please use LIBBPF_OPTS() macro in the example, that's how
> > users are normally expected to use OPTS-based APIs anyways. Also there
> > is no need for "./" when specifying file location. This is a different
> > case than running a binary in the shell, where binary is searched in
> > PATH. This is never done when opening files.
> >
> > So all this should be:
> >
> > LIBBPF_OPTS(bpf_object_open_opts, opts, .btf_custom_path = "5.4.0-smaller.btf");
> > struct bpf_object *obj;
> >
>
> I suppose you meant DECLARE_LIBBPF_OPTS(...)

No, actually, we do have LIBBPF_OPTS and DECLARE_LIBBPF_OPTS is just
an (logically) deprecated alias to LIBBPF_OPTS. Minor difference, but
shorter LIBBPF_OPTS is easier to remember.

>
> > obj = bpf_object__open_file("one.bpf.o", &opts);
> >
> > That's all.
> >
> >
> > > +
> > > +  ...
> > > --
> > > 2.25.1
> > >