ftrace: trace single pid for function graph tracer

Impact: New feature

This patch makes the changes to set_ftrace_pid apply to the function
graph tracer.

  # echo $$ > /debugfs/tracing/set_ftrace_pid
  # echo function_graph > /debugfs/tracing/current_tracer

Will cause only the current task to be traced. Note, the trace flags are
also inherited by child processes, so the children of the shell
will also be traced.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/ftrace.c

@@ -48,7 +48,7 @@ int ftrace_enabled __read_mostly;
 static int last_ftrace_enabled;
 
 /* set when tracing only a pid */
-static int ftrace_pid_trace = -1;
+int ftrace_pid_trace = -1;
 
 /* Quick disabling of function tracer. */
 int function_trace_stop;

kernel/trace/trace.c

@@ -1209,6 +1209,9 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
 	int cpu;
 	int pc;
 
+	if (!ftrace_trace_task(current))
+		return 0;
+
 	if (!ftrace_graph_addr(trace->func))
 		return 0;
 

kernel/trace/trace.h

@@ -541,6 +541,16 @@ print_graph_function(struct trace_iterator *iter)
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
+extern int ftrace_pid_trace;
+
+static inline int ftrace_trace_task(struct task_struct *task)
+{
+	if (ftrace_pid_trace < 0)
+		return 1;
+
+	return test_tsk_trace_trace(task);
+}
+
 /*
  * trace_iterator_flags is an enumeration that defines bit
  * positions into trace_flags that controls the output.