[PATCH 1/3] tracing: Document tracefs gid mount option

[Kalesh Singh <kaleshsingh@google.com>]

[1] and [2] introduced a new gid mount options that could apply to a
group to all entries in tracefs.

Document this in the tracing readme.

[1] https://lore.kernel.org/r/20211208075720.4855d180@gandalf.local.home/T/#u
[2] https://lore.kernel.org/r/20211207171729.2a54e1b3@gandalf.local.home/T/#u

Cc: David Howells <dhowells@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
 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