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

On 15/8/26 04:14, Andrii Nakryiko wrote:

On Sun, Aug 9, 2026 at 8:01 AM Leon Hwang [off-list ref] wrote:

quoted

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.

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

quoted

[1] https://lore.kernel.org/bpf/20260606123955.345967-1-jolsa@kernel.org/ (local)

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

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