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

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Message-ID: <20250618072102.1fnuVt8d@linutronix.de>
Date: Wed, 18 Jun 2025 09:21:02 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	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>,
	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 2025-06-17 20:00:23 [+0200], Peter Zijlstra wrote:
> 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.

I don't know what you run but since Debian 11/ Bullseye (v5.10) this happens
more or less on its own. systemd has the proper mount units:
| # mount | grep trace
| tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)
| # ls -lh /sys/kernel/debug/tracing/ > /dev/null
| # mount | grep trace
| tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)
| tracefs on /sys/kernel/debug/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)

This of course doesn't work if you manually mount it to /debug. While a
symlink would work, you still have to touch the boxes.

Sebastian