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Message-ID: <CAEf4BzY7TZRjxpCJM-+LYgEqe23YFj5Uv3isb7gat2-HU4OSng@mail.gmail.com>
Date: Tue, 24 Jun 2025 08:46:48 -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 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).
>
> --
> Best Regards
> Tao Chen
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