linux-kernel - Re: [PATCH bpf-next v6 1/3] bpf: Show precise link_type for {uprobe,kprobe}

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Message-ID: <CAADnVQLWZH0sQk6ni-AWb+SRJ+H_sE=Gvwn3wdu+UC=mJiPPrg@mail.gmail.com>
Date: Tue, 1 Jul 2025 13:39:36 -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>, 
	John Fastabend <john.fastabend@...il.com>, 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>, 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 v6 1/3] bpf: Show precise link_type for
 {uprobe,kprobe}_multi fdinfo

On Fri, Jun 27, 2025 at 1:23 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
>
> As Andrii suggested attach_type can be recorded in bpf_link, there is
> still a 6 byte hole in bpf_link, we can fill the hole with attach_type
> soon.
>
> Co-authored-by: Jiri Olsa <jolsa@...nel.org>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  include/linux/bpf.h      |  1 +
>  kernel/bpf/syscall.c     |  9 ++++++++-
>  kernel/trace/bpf_trace.c | 10 ++++------
>  3 files changed, 13 insertions(+), 7 deletions(-)
>
> Change list:
>   v5 -> v6:
>     - Move flags into bpf_link to get retprobe info
>       directly.(Alexei, Jiri)
>   v5:
>   https://lore.kernel.org/bpf/20250623134342.227347-1-chen.dylane@linux.dev
>
>   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/bpf.h b/include/linux/bpf.h
> index 5b25d278409..3d8fecc9b17 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1702,6 +1702,7 @@ struct bpf_link {
>          * link's semantics is determined by target attach hook
>          */
>         bool sleepable;
> +       u32 flags :8;

There is a 7-byte hole here.
Let's use 'u32 flags' right now and optimize later if necessary.