linux-kernel - [PATCH v2 2/3] tracing: Document tracefs gid mount option

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Message-ID: <20241030171928.4168869-3-kaleshsingh@google.com>
Date: Wed, 30 Oct 2024 10:17:49 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: dhowells@...hat.com, rostedt@...dmis.org, mhiramat@...nel.org, 
	sandeen@...hat.com
Cc: surenb@...gle.com, jyescas@...gle.com, kernel-team@...roid.com, 
	android-mm@...gle.com, Kalesh Singh <kaleshsingh@...gle.com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Shuah Khan <shuah@...nel.org>, 
	Ali Zahraee <ahzahraee@...il.com>, Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: [PATCH v2 2/3] tracing: Document tracefs gid mount option

Commit ee7f3666995d ("tracefs: Have new files inherit the ownership
of their parent") and commit 48b27b6b5191 ("tracefs: Set all files to
the same group ownership as the mount option") introduced a new gid
mount option that allows specifying a group to apply to all entries
in tracefs.

Document this in the tracing readme.

Cc: Eric Sandeen <sandeen@...hat.com>
Cc: David Howells <dhowells@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
---

Changes in v2:
  - Reference commits instead of lore links, per Steve

 kernel/trace/trace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a8f52b6527ca..2b64b3ec67d9 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5501,6 +5501,10 @@ static const struct file_operations tracing_iter_fops = {

 static const char readme_msg[] =
 	"tracing mini-HOWTO:\n\n"
+	"By default tracefs removes all OTH file permission bits.\n"
+	"When mounting tracefs an optional group id can be specified\n"
+	"which adds the group to every directory and file in tracefs:\n\n"
+	"\t e.g. mount -t tracefs [-o [gid=<gid>]] nodev /sys/kernel/tracing\n\n"
 	"# echo 0 > tracing_on : quick way to disable tracing\n"
 	"# echo 1 > tracing_on : quick way to re-enable tracing\n\n"
 	" Important files:\n"
--
2.47.0.163.g1226f6d8fa-goog