[RFC][PATCH 3/4] ftrace: Have function tracing start in early boot up

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

Register the function tracer right after the tracing buffers are initialized
in early boot up. This will allow function tracing to begin early if it is
enabled via the kernel command line.

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace.c           | 3 +++
 kernel/trace/trace.h           | 2 ++
 kernel/trace/trace_functions.c | 3 +--
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c4c21de61145..b8f7f5cc11b0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7965,6 +7965,9 @@ __init static int tracer_alloc_buffers(void)
 
 	register_tracer(&nop_trace);
 
+	/* Function tracing may start here (via kernel command line) */
+	init_function_trace();
+
 	/* All seems OK, enable tracing */
 	tracing_disabled = 0;
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index ae1cce91fead..d8cbad40d3e2 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -896,6 +896,7 @@ int using_ftrace_ops_list_func(void);
 void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d_tracer);
 void ftrace_init_tracefs_toplevel(struct trace_array *tr,
 				  struct dentry *d_tracer);
+int init_function_trace(void);
 #else
 static inline int ftrace_trace_task(struct trace_array *tr)
 {
@@ -914,6 +915,7 @@ ftrace_init_global_array_ops(struct trace_array *tr) { }
 static inline void ftrace_reset_array_ops(struct trace_array *tr) { }
 static inline void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d) { }
 static inline void ftrace_init_tracefs_toplevel(struct trace_array *tr, struct dentry *d) { }
+static inline int init_function_trace(void) { }
 /* ftace_func_t type is not defined, use macro instead of static inline */
 #define ftrace_init_array_ops(tr, func) do { } while (0)
 #endif /* CONFIG_FUNCTION_TRACER */
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 0efa00d80623..4199ca61b0e5 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -687,9 +687,8 @@ static inline int init_func_cmd_traceon(void)
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
-static __init int init_function_trace(void)
+__init int init_function_trace(void)
 {
 	init_func_cmd_traceon();
 	return register_tracer(&function_trace);
 }
-core_initcall(init_function_trace);
-- 
2.10.2