linux-kernel - Re: [PATCH bpf-next v4 2/2] bpf: Add show_fdinfo for kprobe

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Message-ID: <b2656172-091a-435b-a197-6472ca9a038a@linux.dev>
Date: Mon, 23 Jun 2025 10:32:28 +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 v4 2/2] bpf: Add show_fdinfo for kprobe_multi

在 2025/6/21 02:25, Alexei Starovoitov 写道:
> On Thu, Jun 19, 2025 at 8:31 PM Tao Chen <chen.dylane@...ux.dev> wrote:
>>
>> 在 2025/6/20 10:59, Alexei Starovoitov 写道:
>>> On Thu, Jun 19, 2025 at 7:46 PM Tao Chen <chen.dylane@...ux.dev> wrote:
>>>>
>>>> 在 2025/6/20 01:17, Alexei Starovoitov 写道:
>>>>> On Wed, Jun 18, 2025 at 8:44 PM 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
>>>>>
>>>>> ..
>>>>>
>>>>>> +       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",
>>>>>
>>>>> why print the same info twice ?
>>>>> seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
>>>>> in bpf_link_show_fdinfo() already did it in a cleaner way.
>>>>>
>>>>
>>>> link_type only shows 'kprobe_multi', maybe we can show the format like:
>>>
>>> Ohh. Especially so. It would be wrong and confusing to display:
>>> link_type:      kprobe_multi
>>> type: kretprobe_multi
>>>
>>> Let's fix 'link_type' to display it properly.
>>
>> What do you think show like this:
>>
>>       link_type:      kprobe_multi
>>       link_id:        1
>>       prog_tag:       33be53a4fd673e1d
>>       prog_id:        21
>>       retprobe:       false
> 
> It leaks implementation details.
> For the kernel the link type is BPF_LINK_TYPE_KPROBE_MULTI for retprobe too,
> but show_fdinfo is for humans.
> 'link_type:' field can be more precise and differentiate
> what's effectively a subtype of the link.

Well, i will fix it in v5. Thanks.

-- 
Best Regards
Tao Chen