linux-kernel - Re: [PATCH bpf-next] libbpf: allow disabling auto attach

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Date:   Tue, 16 Aug 2022 15:55:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Hao Luo <haoluo@...gle.com>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH bpf-next] libbpf: allow disabling auto attach

On Tue, Aug 16, 2022 at 3:16 PM Hao Luo <haoluo@...gle.com> wrote:
>
> On Tue, Aug 16, 2022 at 3:01 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Tue, Aug 16, 2022 at 2:49 PM Hao Luo <haoluo@...gle.com> wrote:
> > >
> > > Add libbpf APIs for disabling auto-attach for individual functions.
> > > This is motivated by the use case of cgroup iter [1]. Some iter
> > > types require their parameters to be non-zero, therefore applying
> > > auto-attach on them will fail. With these two new APIs, Users who
> > > want to use auto-attach and these types of iters can disable
> > > auto-attach for them and perform manual attach.
> > >
> > > [1] https://lore.kernel.org/bpf/CAEf4BzZ+a2uDo_t6kGBziqdz--m2gh2_EUwkGLDtMd65uwxUjA@mail.gmail.com/
> > >
> > > Signed-off-by: Hao Luo <haoluo@...gle.com>
> > > ---
> > >  tools/lib/bpf/libbpf.c | 16 ++++++++++++++++
> > >  tools/lib/bpf/libbpf.h |  2 ++
> > >  2 files changed, 18 insertions(+)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index aa05a99b913d..25f654d25b46 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> [...]
> > >  const struct bpf_insn *bpf_program__insns(const struct bpf_program *prog)
> > >  {
> > >         return prog->insns;
> > > @@ -12349,6 +12362,9 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
> > >                 if (!prog->autoload)
> > >                         continue;
> > >
> > > +               if (!prog->autoattach)
> > > +                       continue;
> > > +
> >
> > nit: I'd combine as if (!prog->autoload || !prog->autoattach), they
> > are very coupled in this sense
> >
>
> Sure.
>
> > >                 /* auto-attaching not supported for this program */
> > >                 if (!prog->sec_def || !prog->sec_def->prog_attach_fn)
> > >                         continue;
> > > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > > index 61493c4cddac..88a1ac34b12a 100644
> > > --- a/tools/lib/bpf/libbpf.h
> > > +++ b/tools/lib/bpf/libbpf.h
> > > @@ -260,6 +260,8 @@ LIBBPF_API const char *bpf_program__name(const struct bpf_program *prog);
> > >  LIBBPF_API const char *bpf_program__section_name(const struct bpf_program *prog);
> > >  LIBBPF_API bool bpf_program__autoload(const struct bpf_program *prog);
> > >  LIBBPF_API int bpf_program__set_autoload(struct bpf_program *prog, bool autoload);
> > > +LIBBPF_API bool bpf_program__autoattach(const struct bpf_program *prog);
> > > +LIBBPF_API void bpf_program__set_autoattach(struct bpf_program *prog, bool autoattach);
> >
> > please add these APIs to libbpf.map as well
> >
>
> Ok. Which section? LIBBPF_1.0.0? Do the items in each section have a
> particular order?

Yes, 1.0.0 section. All the functions are sorted alphabetically.

> > it would be also nice to have a simple test validating that skeleton's
> > auto-attach doesn't attach program (no link will be created) if
> > bpf_program__set_autoattach(false) is called before. Can you please
> > add that as well?
> >
>
> Ok. Will add a test and send v2.
>
> > >
> > >  struct bpf_insn;
> > >
> > > --
> > > 2.37.1.595.g718a3a8f04-goog
> > >