linux-kernel - Re: [PATCH bpf-next v5 1/3] bpf: Show precise link_type for {uprobe,kprobe}

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Message-ID: <CAADnVQ+aZw4-3Ab9nLWrZUg78sc-SXuEGYnPrdOChw8m9sRLvw@mail.gmail.com>
Date: Mon, 23 Jun 2025 10:55:59 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: KP Singh <kpsingh@...nel.org>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Song Liu <song@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 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>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...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 v5 1/3] bpf: Show precise link_type for
 {uprobe,kprobe}_multi fdinfo

On Mon, Jun 23, 2025 at 6:44 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>
> Alexei suggested, 'link_type' can be more precise and differentiate
> for human in fdinfo. In fact BPF_LINK_TYPE_KPROBE_MULTI includes
> kretprobe_multi type, the same as BPF_LINK_TYPE_UPROBE_MULTI, so we
> can show it more concretely.
>
> link_type:      kprobe_multi
> link_id:        1
> prog_tag:       d2b307e915f0dd37
> ...
> link_type:      kretprobe_multi
> link_id:        2
> prog_tag:       ab9ea0545870781d
> ...
> link_type:      uprobe_multi
> link_id:        9
> prog_tag:       e729f789e34a8eca
> ...
> link_type:      uretprobe_multi
> link_id:        10
> prog_tag:       7db356c03e61a4d4
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  include/linux/trace_events.h | 10 ++++++++++
>  kernel/bpf/syscall.c         |  9 ++++++++-
>  kernel/trace/bpf_trace.c     | 28 ++++++++++++++++++++++++++++
>  3 files changed, 46 insertions(+), 1 deletion(-)
>
> Change list:
>   v4 -> v5:
>     - Add patch1 to show precise link_type for
>       {uprobe,kprobe}_multi.(Alexei)
>     - patch2,3 just remove type field, which will be showed in
>       link_type
>   v4:
>   https://lore.kernel.org/bpf/20250619034257.70520-1-chen.dylane@linux.dev
>
>   v3 -> v4:
>     - use %pS to print func info.(Alexei)
>   v3:
>   https://lore.kernel.org/bpf/20250616130233.451439-1-chen.dylane@linux.dev
>
>   v2 -> v3:
>     - show info in one line for multi events.(Jiri)
>   v2:
>   https://lore.kernel.org/bpf/20250615150514.418581-1-chen.dylane@linux.dev
>
>   v1 -> v2:
>     - replace 'func_cnt' with 'uprobe_cnt'.(Andrii)
>     - print func name is more readable and security for kprobe_multi.(Alexei)
>   v1:
>   https://lore.kernel.org/bpf/20250612115556.295103-1-chen.dylane@linux.dev
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index fa9cf4292df..951c91babbc 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -780,6 +780,8 @@ int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
>                             unsigned long *missed);
>  int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
>  int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> +void bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
> +void bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
>  #else
>  static inline unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
>  {
> @@ -832,6 +834,14 @@ bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>  {
>         return -EOPNOTSUPP;
>  }
> +static inline void
> +bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
> +{
> +}
> +static inline void
> +bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
> +{
> +}
>  #endif
>
>  enum {
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 51ba1a7aa43..43b821b37bc 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3226,9 +3226,16 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
>         const struct bpf_prog *prog = link->prog;
>         enum bpf_link_type type = link->type;
>         char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
> +       char link_type[64] = {};
>
>         if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) {
> -               seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> +               if (link->type == BPF_LINK_TYPE_KPROBE_MULTI)
> +                       bpf_kprobe_multi_link_type_show(link, link_type, sizeof(link_type));
> +               else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI)
> +                       bpf_uprobe_multi_link_type_show(link, link_type, sizeof(link_type));
> +               else
> +                       strscpy(link_type, bpf_link_type_strs[type], sizeof(link_type));
> +               seq_printf(m, "link_type:\t%s\n", link_type);

New callbacks just to print a string?
Let's find a different way.

How about moving 'flags' from bpf_[ku]probe_multi_link into bpf_link ?
(There is a 7 byte hole there anyway)
and checking flags inline.

Jiri, Andrii,

better ideas?