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

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Message-ID: <20241101183355.620763892@goodmis.org>
Date: Fri, 01 Nov 2024 14:33:29 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Eric Sandeen <sandeen@...hat.com>,
 Shuah Khan <shuah@...nel.org>,
 Ali Zahraee <ahzahraee@...il.com>,
 Christian Brauner <brauner@...nel.org>,
 David Howells <dhowells@...hat.com>,
 Kalesh Singh <kaleshsingh@...gle.com>
Subject: [for-linus][PATCH 2/3] tracing: Document tracefs gid mount option

From: Kalesh Singh <kaleshsingh@...gle.com>

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: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Ali Zahraee <ahzahraee@...il.com>
Cc: Christian Brauner <brauner@...nel.org>
Cc: David Howells <dhowells@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Link: https://lore.kernel.org/20241030171928.4168869-3-kaleshsingh@google.com
Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 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"
-- 
2.45.2