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Date: Mon, 1 Apr 2024 11:59:28 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
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Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add
 support to record and check the accessed args
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On Mon, 1 Apr 2024 10:28:17 +0800
=E6=A2=A6=E9=BE=99=E8=91=A3 <dongmenglong.8@bytedance.com> wrote:

> On Sun, Mar 31, 2024 at 3:34=E2=80=AFAM Steven Rostedt <rostedt@goodmis.o=
rg> wrote:
> >
> > On Sat, 30 Mar 2024 11:18:29 +0800
> > =E6=A2=A6=E9=BE=99=E8=91=A3 <dongmenglong.8@bytedance.com> wrote:
> > =20
> > > > If you really want to have thousands of functions, why not just reg=
ister it
> > > > with ftrace itself. It will give you the arguments via the ftrace_r=
egs
> > > > structure. Can't you just register a program as the callback?
> > > > =20
> > >
> > > Ennn...I don't understand. The main purpose for
> > > me to use TRACING is:
> > >
> > > 1. we can directly access the memory, which is more
> > >    efficient. =20
> >
> > I'm not sure what you mean by the above. Access what memory?
> > =20
>=20
> We need to use the helper of bpf_probe_read_kernel
> when we read "skb->sk" in kprobe, and the "skb" is the
> 1st arg in ip_rcv(). And we can directly read "skb->sk"
> in tracing, which is more efficient. Isn't it?

If you add a ftrace_ops function handler that calls a BPF program, I don't
see why you can't just give it the parameters it needs instead of using bpf
helpers. It's no different than using a trampoline to do the same thing.

-- Steve