linux-kernel - Re: [PATCH] Documentation: tracing: Add documentation about eprobes

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Message-ID: <20250729115446.06aa72e4@batman.local.home>
Date: Tue, 29 Jul 2025 11:54:46 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux trace kernel
 <linux-trace-kernel@...r.kernel.org>, linux-doc@...r.kernel.org, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Mark Rutland
 <mark.rutland@....com>, Andrew Morton <akpm@...ux-foundation.org>, Namhyung
 Kim <namhyung@...nel.org>, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] Documentation: tracing: Add documentation about eprobes

On Tue, 29 Jul 2025 10:26:36 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > diff --git a/Documentation/trace/eprobes.rst b/Documentation/trace/eprobes.rst
> > new file mode 100644
> > index 000000000000..c7aa7c867e9e
> > --- /dev/null
> > +++ b/Documentation/trace/eprobes.rst  
> 
> BTW, can't you rename it as 'eprobetrace.rst' as same as others?
> I usually name the doc of "a probe feature which provides only in-kernel
> APIs" as '*probe.rst' and the doc of "a probe *event* feature which can
> controlled via tracefs interface" as '*probetrace.rst'.

Sure, no problem. Will update.

> 
> > @@ -0,0 +1,268 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +=====================
> > +Eprobe - Event probes  
> 
> What about below title?
> 
>  Eprobe - Event-based Probe Tracing

OK.

> 
> > +=====================
> > +
> > +:Author: Steven Rostedt <rostedt@...dmis.org>
> > +
> > +- Written for v6.17
> > +
> > +Overview
> > +========
> > +
> > +Eprobes are dynamic events that are placed on existing events to eiter
> > +dereference a field that is a pointer, or simply to limit what fields get
> > +recorded in the trace event.
> > +
> > +Eprobes depend on kprobe events so to enable this feature, build your kernel
> > +with CONFIG_KPROBE_EVENTS=y.  
> 
> Is this correct? It seems that eprobe event only depends on event trigger
> (by implementation. Actually we should fix the kernel/trace/Kconfig.)
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git/tree/kernel/trace/trace_eprobe.c?h=trace-v6.16-rc5#n576

I noticed there was no config that selected it, and it only gets
selected by CONFIG_PROBE_EVENTS which requires something else to select
it. I guess adding an EPROBE config would be useful too. Let me do that
too.

Thanks for the review.

-- Steve