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

[Hao Luo]

On Tue, Aug 16, 2022 at 3:01 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, Aug 16, 2022 at 2:49 PM Hao Luo <haoluo@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/
> >
> > Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
> > ---
> >  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?

> 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
> >