linux-kernel - Re: [PATCH bpf-next v3 2/2] bpf: Add show_fdinfo for kprobe

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Message-ID: <CAADnVQ+hT6nCGoR5a0Z+52SrJzO9-ReBRds23mBfrG3SbwGFdw@mail.gmail.com>
Date: Wed, 18 Jun 2025 18:46:58 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <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>, Jiri Olsa <jolsa@...nel.org>, 
	Matt Bobrowski <mattbobrowski@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 2/2] bpf: Add show_fdinfo for kprobe_multi

On Mon, Jun 16, 2025 at 6:03 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>
> Show kprobe_multi link info with fdinfo, the info as follows:
>
> link_type:      kprobe_multi
> link_id:        1
> prog_tag:       a15b7646cb7f3322
> prog_id:        21
> type:   kprobe_multi
> kprobe_cnt:     8
> missed: 0
> cookie           func
> 1                bpf_fentry_test1
> 7                bpf_fentry_test2
> 2                bpf_fentry_test3
> 3                bpf_fentry_test4
> 4                bpf_fentry_test5
> 5                bpf_fentry_test6
> 6                bpf_fentry_test7
> 8                bpf_fentry_test8
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  kernel/trace/bpf_trace.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 2d422f897ac..fcf19e233b5 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2623,10 +2623,42 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
>         return err;
>  }
>
> +#ifdef CONFIG_PROC_FS
> +static void bpf_kprobe_multi_show_fdinfo(const struct bpf_link *link,
> +                                        struct seq_file *seq)
> +{
> +       struct bpf_kprobe_multi_link *kmulti_link;
> +       char sym[KSYM_NAME_LEN];
> +
> +       kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
> +
> +       seq_printf(seq,
> +                  "type:\t%s\n"
> +                  "kprobe_cnt:\t%u\n"
> +                  "missed:\t%lu\n",
> +                  kmulti_link->flags == BPF_F_KPROBE_MULTI_RETURN ? "kretprobe_multi" :
> +                                        "kprobe_multi",
> +                  kmulti_link->cnt,
> +                  kmulti_link->fp.nmissed);
> +
> +       seq_printf(seq, "%-16s %-16s\n", "cookie", "func");
> +       for (int i = 0; i < kmulti_link->cnt; i++) {
> +               sprint_symbol_no_offset(sym, kmulti_link->addrs[i]);
> +               seq_printf(seq,
> +                          "%-16llu %-16s\n",
> +                          kmulti_link->cookies[i],
> +                          sym);

Why call sprint_symbol_no_offset() directly ?
%pB is fine.
+off doesn't disclose anything.

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