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

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Date:   Thu, 3 Feb 2022 18:12:11 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jiri Olsa <olsajiri@...il.com>
Subject: Re: [PATCH 0/8] bpf: Add fprobe link

On Thu, Feb 3, 2022 at 6:07 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Thu, 3 Feb 2022 17:34:54 -0800
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
>
> > On Thu, Feb 3, 2022 at 4:46 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > >
> > > I thought What Alexei pointed was that don't expose the FPROBE name
> > > to user space. If so, I agree with that. We can continue to use
> > > KPROBE for user space. Using fprobe is just for kernel implementation.
> >
> > Clearly that intent is not working.
>
> Thanks for confirmation :-)
>
> > The "fprobe" name is already leaking outside of the kernel internals.
> > The module interface is being proposed.
>
> Yes, but that is only for making the example module.
> It is easy for me to enclose it inside kernel. I'm preparing KUnit
> selftest code for next version. After integrated that, we don't need
> that example module anymore.
>
> > You'd need to document it, etc.
>
> Yes, I've added a document of the APIs for the series.  :-)
>
> > I think it's only causing confusion to users.
> > The new name serves no additional purpose other than
> > being new and unheard of.
> > fprobe is kprobe on ftrace. That's it.
>
> No, fprobe is NOT kprobe on ftrace, kprobe on ftrace is already implemented
> transparently.

Not true.
fprobe is nothing but _explicit_ kprobe on ftrace.
There was an implicit optimization for kprobe when ftrace
could be used.
All this new interface is doing is making it explicit.
So a new name is not warranted here.

> from that viewpoint, fprobe and kprobe interface are similar but different.

What is the difference?
I don't see it.