tracing: Support multiple pids in set_pid_ftrace file

Adding the possibility to set more than 1 pid in the set_pid_ftrace
file, thus allowing to trace more than 1 independent processes.

Usage:

 sh-4.0# echo 284 > ./set_ftrace_pid
 sh-4.0# cat ./set_ftrace_pid
 284
 sh-4.0# echo 1 >> ./set_ftrace_pid
 sh-4.0# echo 0 >> ./set_ftrace_pid
 sh-4.0# cat ./set_ftrace_pid
 swapper tasks
 1
 284
 sh-4.0# echo 4 > ./set_ftrace_pid
 sh-4.0# cat ./set_ftrace_pid
 4
 sh-4.0# echo > ./set_ftrace_pid
 sh-4.0# cat ./set_ftrace_pid
 no pid
 sh-4.0#

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20091013203425.565454612@goodmis.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f22a7ac32380..acef8b4636f0 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -496,12 +496,12 @@ print_graph_function(struct trace_iterator *iter)
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
-extern struct pid *ftrace_pid_trace;
+extern struct list_head ftrace_pids;
 
 #ifdef CONFIG_FUNCTION_TRACER
 static inline int ftrace_trace_task(struct task_struct *task)
 {
-        if (!ftrace_pid_trace)
+        if (list_empty(&ftrace_pids))
                 return 1;
 
         return test_tsk_trace_trace(task);