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Message-ID: <CAEf4BzambK3=3pPbW=xaiQH9WZ7_drb0wsXbKLNQn6n2Skt9zg@mail.gmail.com>
Date: Tue, 24 Jun 2025 12:41:58 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: Jiri Olsa <olsajiri@...il.com>, 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
On Tue, Jun 24, 2025 at 9:13 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>
> 在 2025/6/24 23:46, Andrii Nakryiko 写道:
> > On Tue, Jun 24, 2025 at 1:41 AM Tao Chen <chen.dylane@...ux.dev> wrote:
> >>
> >> 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.
> >
> > You are right, I somehow was under impression that ret vs non-retprobe
> > comes from attach type as well.
> >
> > Ok, moving flags into common bpf_link struct sounds good to me. I'd
> > still move attach_type into bpf_link, together with flags, for
> > generality (and update all those links that already include
> > attach_type as you mentioned). We can make it a single-byte field to
> > not increase bpf_link size unnecessarily (by using bitfield size).
> >
>
> Well，can we complete this in two steps?
>
sure, of course
> 1. Create a common field in bpf_link used for flags or attach_type, and
> realise the precise link_type feature as Jiri and Alexei said, the
> review of this part has been revised almost completely.
>
> 2. Move the attach_type from struct bpf_xx_link into bpf_link, this will
> involve a lot of changes, i will send a separate patchset to finish it.
>
> >>
> >> --
> >> Best Regards
> >> Tao Chen
>
>
> --
> Best Regards
> Tao Chen
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