[RFC PATCH 1/2] ftrace: Introduce cmdline argument ftrace_disabled

[Tiezhu Yang]

If set CONFIG_FUNCTION_TRACER=y, we can use the following command to
disable ftrace after boot up:
echo 0 > /proc/sys/kernel/ftrace_enabled

ftrace_disabled is much stronger than ftrace_enabled, introduce a new
cmdline argument ftrace_disabled for user to control whether to disable
ftrace when boot up.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 kernel/trace/ftrace.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 72ef4dc..a015699 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5517,6 +5517,14 @@ static char ftrace_filter_buf[FTRACE_FILTER_SIZE] __initdata;
 /* Used by function selftest to not test if filter is set */
 bool ftrace_filter_param __initdata;
 
+static int __init set_ftrace_disabled(char *str)
+{
+	pr_info("Set ftrace_disabled to disable ftrace\n");
+	ftrace_disabled = 1;
+	return 1;
+}
+__setup("ftrace_disabled", set_ftrace_disabled);
+
 static int __init set_ftrace_notrace(char *str)
 {
 	ftrace_filter_param = true;
-- 
2.1.0