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Message-ID: <CAEf4BzZVw4aSpdTH+VKkG_q6J-sQwSFSCyU+-c5DcA5euP49ng@mail.gmail.com>
Date: Mon, 23 Jun 2025 13:59:18 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Tao Chen <chen.dylane@...ux.dev>, KP Singh <kpsingh@...nel.org>,
Matt Bobrowski <mattbobrowski@...gle.com>, Song Liu <song@...nel.org>, Jiri Olsa <jolsa@...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 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
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