Re: [PATCH 0/8] bpf: Add fprobe link

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Jiri Olsa <olsajiri@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Jiri Olsa <jolsa@redhat.com>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, lkml <linux-kernel@vger.kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>, Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 0/8] bpf: Add fprobe link
Date: Fri, 18 Feb 2022 13:07:27 +0900	[thread overview]
Message-ID: <20220218130727.51db96861c3e1c79b45daafb@kernel.org> (raw)
In-Reply-To: <CAEf4BzYxcSCae=sF3EKNUtLDCZhkhHkd88CEBt4bffzN_AZrDw@mail.gmail.com>

On Thu, 17 Feb 2022 14:01:30 -0800
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> > > Is there any chance to support this fast multi-attach for uprobe? If
> > > yes, we might want to reuse the same link for both (so should we name
> > > it more generically?
> >
> > There is no interface to do that but also there is no limitation to
> > expand uprobes. For the kprobes, there are some limitations for the
> > function entry because it needs to share the space with ftrace. So
> > I introduced fprobe for easier to use.
> >
> > > on the other hand BPF program type for uprobe is
> > > BPF_PROG_TYPE_KPROBE anyway, so keeping it as "kprobe" also would be
> > > consistent with what we have today).
> >
> > Hmm, I'm not sure why BPF made such design choice... (Uprobe needs
> > the target program.)
> >
> 
> We've been talking about sleepable uprobe programs, so we might need
> to add uprobe-specific program type, probably. But historically, from
> BPF point of view there was no difference between kprobe and uprobe
> programs (in terms of how they are run and what's available to them).
> From BPF point of view, it was just attaching BPF program to a
> perf_event.

Got it, so that will reuse the uprobe_events in ftrace. But I think
the uprobe requires a "path" to the attached binary, how is it
specified?

> > > But yeah, the main question is whether there is something preventing
> > > us from supporting multi-attach uprobe as well? It would be really
> > > great for USDT use case.
> >
> > Ah, for the USDT, it will be useful. But since now we will have "user-event"
> > which is faster than uprobes, we may be better to consider to use it.
> 
> Any pointers? I'm not sure what "user-event" refers to.

Here is the user-events series, which allows user program to define
raw dynamic events and it can write raw event data directly from
user space.

https://lore.kernel.org/all/20220118204326.2169-1-beaub@linux.microsoft.com/

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>