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

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Message-ID: <7b6ae7dc-1044-4551-bc3f-32430e34ba05@linux.dev>
Date: Thu, 19 Jun 2025 11:08:15 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
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

在 2025/6/19 09:46, Alexei Starovoitov 写道:
> 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.
> 
> pw-bot: cr

My problem, sorry for that, i had some issues with using printk to show 
func name directly before. Actually, i used it incorrectly. How about 
%pS, it looks more accurate. Thanks!

%pB format
cookie           func
8                __pfx_bpf_fentry_test1+0x10/0x10
2                __pfx_bpf_fentry_test2+0x10/0x10
7                __pfx_bpf_fentry_test3+0x10/0x10

%pS format
cookie           func
8                bpf_fentry_test1+0x0/0x20
2                bpf_fentry_test2+0x0/0x20
7                bpf_fentry_test3+0x0/0x20

-- 
Best Regards
Tao Chen