linux-kernel - Re: [PATCH bpf-next v2 15/18] libbpf: add skip_invalid and attach_tracing for tracing

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Message-ID: <CAEf4BzZb793wAXROPNcE_EggfU1U3g80jdDsvP5sr86uDBhgmA@mail.gmail.com>
Date: Mon, 14 Jul 2025 15:07:47 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: alexei.starovoitov@...il.com, rostedt@...dmis.org, jolsa@...nel.org, 
	bpf@...r.kernel.org, Menglong Dong <dongml2@...natelecom.cn>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 15/18] libbpf: add skip_invalid and
 attach_tracing for tracing_multi

On Thu, Jul 3, 2025 at 5:23 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> We add skip_invalid and attach_tracing for tracing_multi for the
> selftests.
>
> When we try to attach all the functions in available_filter_functions with
> tracing_multi, we can't tell if the target symbol can be attached
> successfully, and the attaching will fail. When skip_invalid is set to
> true, we will check if it can be attached in libbpf, and skip the invalid
> entries.
>
> We will skip the symbols in the following cases:
>
> 1. the btf type not exist
> 2. the btf type is not a function proto
> 3. the function args count more that 6
> 4. the return type is struct or union
> 5. any function args is struct or union
>
> The 5th rule can be a manslaughter, but it's ok for the testings.
>
> "attach_tracing" is used to convert a TRACING prog to TRACING_MULTI. For
> example, we can set the attach type to FENTRY_MULTI before we load the
> skel. And we can attach the prog with
> bpf_program__attach_trace_multi_opts() with "attach_tracing=1". The libbpf
> will attach the target btf type of the prog automatically. This is also
> used to reuse the selftests of tracing.
>
> (Oh my goodness! What am I doing?)

exactly...

Let's think if we need any of that, as in: take a step back, and try
to explain why you think any of this should be part of libbpf's UAPI.

>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
>  tools/lib/bpf/libbpf.c | 97 ++++++++++++++++++++++++++++++++++++------
>  tools/lib/bpf/libbpf.h |  6 ++-
>  2 files changed, 89 insertions(+), 14 deletions(-)
>

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