netdev - Re: [RFC PATCH bpf-next 1/2] libbpf: Add support for dynamic tracepoint

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Message-ID: <Z30bGYeyGQL2UpnX@krava>
Date: Tue, 7 Jan 2025 13:16:25 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>, Eddy Z <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Eric Dumazet <edumazet@...gle.com>,
	bpf <bpf@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Viktor Malik <vmalik@...hat.com>
Subject: Re: [RFC PATCH bpf-next 1/2] libbpf: Add support for dynamic
 tracepoint

On Mon, Jan 06, 2025 at 10:32:15AM +0800, Yafang Shao wrote:
> On Mon, Jan 6, 2025 at 8:16 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Sun, Jan 5, 2025 at 4:44 AM Yafang Shao <laoar.shao@...il.com> wrote:
> > >
> > > Dynamic tracepoints can be created using debugfs. For example:
> > >
> > >    echo 'p:myprobe kernel_clone args' >> /sys/kernel/debug/tracing/kprobe_events
> > >
> > > This command creates a new tracepoint under debugfs:
> > >
> > >   $ ls /sys/kernel/debug/tracing/events/kprobes/myprobe/
> > >   enable  filter  format  hist  id  trigger
> > >
> > > Although this dynamic tracepoint appears as a tracepoint, it is internally
> > > implemented as a kprobe. However, it must be attached as a tracepoint to
> > > function correctly in certain contexts.
> >
> > Nack.
> > There are multiple mechanisms to create kprobe/tp via text interfaces.
> > We're not going to mix them with the programmatic libbpf api.
> 
> It appears that bpftrace still lacks support for adding a kprobe/tp
> and then attaching to it directly. Is that correct?
> What do you think about introducing this mechanism into bpftrace? With
> such a feature, we could easily attach to inlined kernel functions
> using bpftrace.

so with the 'echo .. > kprobe_events' you create kprobe which will be
exported through tracefs together with other tracepoints and bpftrace
sees it as another tracepoint.. but it's a kprobe :-\

how about we add support for kprobe section like SEC("kprobe/SUBSYSTEM/PROBE"),
so in your case above it'd be SEC("kprobe/kprobes/myprobe")

then attach_kprobe would parse that out and use new new probe_attach_mode
for bpf_program__attach_kprobe_opts to attach it correctly

cc-ing Viktor

jirka