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Message-ID: <9034e367-e7e1-43b5-bd7c-70fc9a58335d@linux.dev>
Date: Tue, 24 Jun 2025 16:41:17 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Jiri Olsa <olsajiri@...il.com>,
Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
KP Singh <kpsingh@...nel.org>, Matt Bobrowski <mattbobrowski@...gle.com>,
Song Liu <song@...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
在 2025/6/24 16:16, Jiri Olsa 写道:
> On Mon, Jun 23, 2025 at 01:59:18PM -0700, Andrii Nakryiko wrote:
>> On Mon, Jun 23, 2025 at 10:56 AM Alexei Starovoitov
>> <alexei.starovoitov@...il.com> wrote:
>>>
>>> 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?
>>
>> We can just remember original attr->link_create.attach_type in
>> bpf_link itself, and then have a small helper that will accept link
>> type and attach type, and fill out link type representation based on
>> those two. Internally we can do the special-casing of uprobe vs
>> uretprobe and kprobe vs kretprobe transparently to all the other code.
>> And use that here in show_fdinfo
>
> but you'd still need the flags, no? to find out if it's return probe
>
> I tried what Alexei suggested and it seems ok and simple enough
>
> jirka
>
>
> ---
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 5dd556e89cce..287c956cdbd2 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;
> /* rcu is used before freeing, work can be used to schedule that
> * RCU-based freeing before that, so they never overlap
> */
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 56500381c28a..f1d9ee9717a1 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3228,7 +3228,14 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
> char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
>
> 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)
> + seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_KPROBE_MULTI_RETURN ?
> + "kretprobe_multi" : "kprobe_multi");
> + else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI)
> + seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_UPROBE_MULTI_RETURN ?
> + "uretprobe_multi" : "uprobe_multi");
> + else
> + seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> } else {
> WARN_ONCE(1, "missing BPF_LINK_TYPE(...) for link type %u\n", type);
> seq_printf(m, "link_type:\t<%u>\n", type);
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0a06ea6638fe..81d7a4e5ae15 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2466,7 +2466,6 @@ struct bpf_kprobe_multi_link {
> u32 cnt;
> u32 mods_cnt;
> struct module **mods;
> - u32 flags;
> };
>
> struct bpf_kprobe_multi_run_ctx {
> @@ -2586,7 +2585,7 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
>
> kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
> info->kprobe_multi.count = kmulti_link->cnt;
> - info->kprobe_multi.flags = kmulti_link->flags;
> + info->kprobe_multi.flags = kmulti_link->link.flags;
> info->kprobe_multi.missed = kmulti_link->fp.nmissed;
>
> if (!uaddrs)
> @@ -2976,7 +2975,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> link->addrs = addrs;
> link->cookies = cookies;
> link->cnt = cnt;
> - link->flags = flags;
> + link->link.flags = flags;
>
> if (cookies) {
> /*
> @@ -3045,7 +3044,6 @@ struct bpf_uprobe_multi_link {
> struct path path;
> struct bpf_link link;
> u32 cnt;
> - u32 flags;
> struct bpf_uprobe *uprobes;
> struct task_struct *task;
> };
> @@ -3109,7 +3107,7 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
>
> umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> info->uprobe_multi.count = umulti_link->cnt;
> - info->uprobe_multi.flags = umulti_link->flags;
> + info->uprobe_multi.flags = umulti_link->link.flags;
> info->uprobe_multi.pid = umulti_link->task ?
> task_pid_nr_ns(umulti_link->task, task_active_pid_ns(current)) : 0;
>
> @@ -3369,7 +3367,7 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> link->uprobes = uprobes;
> link->path = path;
> link->task = task;
> - link->flags = flags;
> + link->link.flags = flags;
>
> bpf_link_init(&link->link, BPF_LINK_TYPE_UPROBE_MULTI,
> &bpf_uprobe_multi_link_lops, prog);
Hi, Jiri, Andrii,
Jiri's patch looks more simple, and i see other struct xx_links wrap
bpf_link, which have attach_type field like:
struct sockmap_link {
struct bpf_link link;
struct bpf_map *map;
enum bpf_attach_type attach_type;
};
If we create attach_type filed in bpf_link, maybe these struct xx_link
should also be modified. BTW, as Jiri said, we still can not find return
probe type from attach_type.
--
Best Regards
Tao Chen
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