linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Add show_fdinfo for uprobe

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Message-ID: <CAEf4BzbxGS85nKK8qAYkSE1HEj7hVshmr9xGsZcP5di0Fu02xQ@mail.gmail.com>
Date: Thu, 12 Jun 2025 14:27:49 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, 
	mattbobrowski@...gle.com, rostedt@...dmis.org, mhiramat@...nel.org, 
	mathieu.desnoyers@...icios.com, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: Add show_fdinfo for uprobe_multi

On Thu, Jun 12, 2025 at 4:56 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>
> Show uprobe_multi link info with fdinfo, the info as follows:
>
> link_type:      uprobe_multi
> link_id:        9
> prog_tag:       e729f789e34a8eca
> prog_id:        39
> type:   uprobe_multi
> func_cnt:       3
> pid:    0
> path:   /home/dylane/bpf/tools/testing/selftests/bpf/test_progs
> offset: 0xa69ed7
> ref_ctr_offset: 0x0
> cookie: 3
> offset: 0xa69ee2
> ref_ctr_offset: 0x0
> cookie: 1
> offset: 0xa69eed
> ref_ctr_offset: 0x0
> cookie: 2
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  kernel/trace/bpf_trace.c | 48 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 24b94870b50..c4ad82b8fd8 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3157,10 +3157,58 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
>         return err;
>  }
>
> +#ifdef CONFIG_PROC_FS
> +static void bpf_uprobe_multi_show_fdinfo(const struct bpf_link *link,
> +                                        struct seq_file *seq)
> +{
> +       struct bpf_uprobe_multi_link *umulti_link;
> +       char *p, *buf;
> +
> +       umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> +
> +       buf = kmalloc(PATH_MAX, GFP_KERNEL);
> +       if (!buf)
> +               return;
> +
> +       p = d_path(&umulti_link->path, buf, PATH_MAX);
> +       if (IS_ERR(p)) {
> +               kfree(buf);
> +               return;
> +       }
> +
> +       seq_printf(seq,
> +                  "type:\t%s\n"
> +                  "func_cnt:\t%u\n"

it's not really *func* (e.g., for USDTs it's basically guaranteed to
be somewhere inside the function, potentially in many places within
the same function), I'd use generic "uprobe_{cnt,count}"


> +                  "pid:\t%u\n"
> +                  "path:\t%s\n",
> +                  umulti_link->flags == BPF_F_UPROBE_MULTI_RETURN ?
> +                                        "uretprobe_multi" : "uprobe_multi",
> +                  umulti_link->cnt,
> +                  umulti_link->task ? task_pid_nr_ns(umulti_link->task,
> +                          task_active_pid_ns(current)) : 0,
> +                  p);
> +
> +       for (int i = 0; i < umulti_link->cnt; i++) {
> +               seq_printf(seq,
> +                          "offset:\t%#llx\n"
> +                          "ref_ctr_offset:\t%#lx\n"
> +                          "cookie:\t%llu\n",
> +                          umulti_link->uprobes[i].offset,
> +                          umulti_link->uprobes[i].ref_ctr_offset,
> +                          umulti_link->uprobes[i].cookie);
> +       }
> +
> +       kfree(buf);
> +}
> +#endif
> +
>  static const struct bpf_link_ops bpf_uprobe_multi_link_lops = {
>         .release = bpf_uprobe_multi_link_release,
>         .dealloc_deferred = bpf_uprobe_multi_link_dealloc,
>         .fill_link_info = bpf_uprobe_multi_link_fill_link_info,
> +#ifdef CONFIG_PROC_FS
> +       .show_fdinfo = bpf_uprobe_multi_show_fdinfo,
> +#endif
>  };
>
>  static int uprobe_prog_run(struct bpf_uprobe *uprobe,
> --
> 2.48.1
>