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

[Leon Hwang]

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.

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