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Message-ID: <aFpeyZnOuJ3Xr4J6@krava>
Date: Tue, 24 Jun 2025 10:16:09 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
Tao Chen <chen.dylane@...ux.dev>, 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 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);
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