ftrace: add ftrace_enabled sysctl to disable mcount function

This patch adds back the sysctl ftrace_enabled. This time it is
defaulted to on, if DYNAMIC_FTRACE is configured. When ftrace_enabled
is disabled, the ftrace function is set to the stub return.

If DYNAMIC_FTRACE is also configured, on ftrace_enabled = 0,
the registered ftrace functions will all be set to jmps, but no more
new calls to ftrace recording (used to find the ftrace calling sites)
will be called.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 90dbc0ee2046..ccd8537dbdb7 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -5,6 +5,12 @@
 
 #include <linux/linkage.h>
 
+extern int ftrace_enabled;
+extern int
+ftrace_enable_sysctl(struct ctl_table *table, int write,
+                     struct file *filp, void __user *buffer, size_t *lenp,
+                     loff_t *ppos);
+
 typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip);
 
 struct ftrace_ops {