linux-kernel - Re: [RFC][PATCH] tracing: Deprecate auto-mounting tracefs in debugfs

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Message-ID: <20250617180023.GC1613376@noisy.programming.kicks-ass.net>
Date: Tue, 17 Jun 2025 20:00:23 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
	"linux-trace-users@...r.kernel.org" <linux-trace-users@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>
Subject: Re: [RFC][PATCH] tracing: Deprecate auto-mounting tracefs in debugfs

On Tue, Jun 17, 2025 at 01:54:46PM -0400, Steven Rostedt wrote:
> 
> 
> On June 17, 2025 1:41:07 PM EDT, Peter Zijlstra <peterz@...radead.org> wrote:
> >On Tue, Jun 17, 2025 at 01:36:14PM -0400, Steven Rostedt wrote:
> >> From: Steven Rostedt <rostedt@...dmis.org>
> >> 
> >> In January 2015, tracefs was created to allow access to the tracing
> >> infrastructure without needing to compile in debugfs. When tracefs is
> >> configured, the directory /sys/kernel/tracing will exist and tooling is
> >> expected to use that path to access the tracing infrastructure.
> >> 
> >> To allow backward compatibility, when debugfs is mounted, it would
> >> automount tracefs in its "tracing" directory so that tooling that had hard
> >> coded /sys/kernel/debug/tracing would still work.
> >> 
> >> It has been over 10 years since the new interface was introduced, and all
> >> tooling should now be using it. Start the process of deprecating the old
> >> path so that it doesn't need to be maintained anymore.
> >
> >I've always used /debug/tracing/ (because /debug is the right place to
> >mount debugfs). You're saying this is going away and will break all my
> >scripts?!
> 
> You could mount tracefs in /tracing too:
> 
>   # mount -t tracefs nodev /tracing 
> 
> And update you scripts with a simple sed script.

If I have to edit the mount table, I'll just keep it at /debug/tracing/.
Tracing is very much debug stuff anyway. While I knew there was tracefs,
I never knew there was another mount point.

Just annoying I now have to add two entries to every new machine.. Oh
well.