Re: [PATCH bpf-next 00/13] bpf: Add tracing_multi link support for bpf progs

[Andrii Nakryiko]

On Sun, Aug 16, 2026 at 11:20 PM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
> On 15/8/26 04:14, Andrii Nakryiko wrote:
> > On Sun, Aug 9, 2026 at 8:01 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
> >>
> >> Similar to the tracing_multi link support for kernel functions [1], add
> >> support for bpf progs.
> >>
> >> When attaching to bpf progs, it must attaches to the target by text poke
> >> way.
> >>
> >
> > Please spend a bit more human effort on justification for the change
> > and explaining your use case. In what case you'll be attaching to a
> > large amount of BPF programs such that attachment speed-up (if there
> > is any) matters.
>
> Will update the cover letter with justification and my use case.
>
> Here's my use case:
>
> I'm planning to enhance the function-graph feature of bpfsnoop [1]. It
> will trace all bpf progs, including their subprogs, to draw a full
> function call graph including bpf prog call sites.
>

fair enough, interesting use case, definitely outline that in the next
revision (and provide before/after attach time as well for such use
case, please)

> The attachment could speed-up when there are hundreds of targets. For
> example, on high CPU core count servers, it probably runs 200 tc-bpf
> progs as Kubernetes CNI, and each tc-bpf prog might have 4 subprogs.
> Hence, there will be 1000 targets to trace for bpfsnoop's function-graph
> feature.
>
> With tracing_multi link support for bpf progs, bpfsnoop will be able to
> attach to all targets quickly.
>
> [1] https://github.com/bpfsnoop/bpfsnoop
>
> >
> > Please do your homework. Generating code with AI is easy, reviewing
>
> Sure, will do my homework.
>
> > and making decisions about whether it's the right approach (and
> > ultimately supporting it long term) is still a human process, so let's
> > weigh that in.
>
> Will keep it in mind.
>
> Thanks,
> Leon
>
> >
> >> [1] https://lore.kernel.org/bpf/20260606123955.345967-1-jolsa@xxxxxxxxxx/
> >>
> >> Leon Hwang (13):
> >>   bpf: Initialize ftrace_managed in bpf_trampoline_get
> >>   bpf: Factor out update_fentry_multi helper
> >>   bpf: Drop unnecessary ftrace_location() in update_fentry_multi()
> >>   bpf: Add tracing_multi link support for bpf progs
> >>   libbpf: Add tracing_multi link support for bpf progs
> >>   bpf: Add tracing_multi link fdinfo support for bpf progs
> >>   bpf: Add tracing_multi link info support for bpf progs
> >>   selftests/bpf: Add tracing_multi bpf prog attach test
> >>   selftests/bpf: Add tracing_multi bpf prog attach failure tests
> >>   selftests/bpf: Add tracing_multi bpf prog cookie test
> >>   selftests/bpf: Add tracing_multi bpf prog rollback test
> >>   selftests/bpf: Add tracing_multi bpf prog link info test
> >>   selftests/bpf: Test tailcall with fentry.multi
> >>
> >>  include/linux/bpf.h                           |   3 +
> >>  include/uapi/linux/bpf.h                      |   6 +-
> >>  kernel/bpf/trampoline.c                       |  87 +++---
> >>  kernel/bpf/verifier.c                         |  22 +-
> >>  kernel/trace/bpf_trace.c                      | 212 ++++++++++++---
> >>  tools/bpf/bpftool/link.c                      |  59 +++-
> >>  tools/include/uapi/linux/bpf.h                |   6 +-
> >>  tools/lib/bpf/bpf.c                           |   1 +
> >>  tools/lib/bpf/bpf.h                           |   2 +
> >>  tools/lib/bpf/libbpf.c                        |  39 ++-
> >>  tools/lib/bpf/libbpf.h                        |   4 +-
> >>  tools/lib/bpf/libbpf_internal.h               |   1 +
> >>  .../selftests/bpf/prog_tests/fill_link_info.c | 170 ++++++++++--
> >>  .../selftests/bpf/prog_tests/tailcalls.c      |  62 +++++
> >>  .../selftests/bpf/prog_tests/tracing_multi.c  | 254 ++++++++++++++++++
> >>  .../selftests/bpf/progs/tracing_multi_bpf.c   |  61 +++++
> >>  16 files changed, 869 insertions(+), 120 deletions(-)
> >>  create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_bpf.c
> >>
> >> --
> >> 2.55.0
>