tracing: Add TRACE_EVENT_FN example
If a function should be called before a tracepoint is enabled
and/or after it is disabled, the TRACE_EVENT_FN() serves this
purpose. But it is not well documented. Having it as a sample would
help developers to know how to use it.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/samples/trace_events/trace-events-sample.c b/samples/trace_events/trace-events-sample.c
index c396a49..39d4484 100644
--- a/samples/trace_events/trace-events-sample.c
+++ b/samples/trace_events/trace-events-sample.c
@@ -49,6 +49,52 @@
}
static struct task_struct *simple_tsk;
+static struct task_struct *simple_tsk_fn;
+
+static void simple_thread_func_fn(int cnt)
+{
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(HZ);
+
+ /* More silly tracepoints */
+ trace_foo_bar_with_fn("Look at me", cnt);
+}
+
+static int simple_thread_fn(void *arg)
+{
+ int cnt = 0;
+
+ while (!kthread_should_stop())
+ simple_thread_func_fn(cnt++);
+
+ return 0;
+}
+
+static DEFINE_MUTEX(thread_mutex);
+
+void foo_bar_reg(void)
+{
+ pr_info("Starting thread for foo_bar_fn\n");
+ /*
+ * We shouldn't be able to start a trace when the module is
+ * unloading (there's other locks to prevent that). But
+ * for consistency sake, we still take the thread_mutex.
+ */
+ mutex_lock(&thread_mutex);
+ simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");
+ mutex_unlock(&thread_mutex);
+}
+
+void foo_bar_unreg(void)
+{
+ pr_info("Killing thread for foo_bar_fn\n");
+ /* protect against module unloading */
+ mutex_lock(&thread_mutex);
+ if (simple_tsk_fn)
+ kthread_stop(simple_tsk_fn);
+ simple_tsk_fn = NULL;
+ mutex_unlock(&thread_mutex);
+}
static int __init trace_event_init(void)
{
@@ -62,6 +108,11 @@
static void __exit trace_event_exit(void)
{
kthread_stop(simple_tsk);
+ mutex_lock(&thread_mutex);
+ if (simple_tsk_fn)
+ kthread_stop(simple_tsk_fn);
+ simple_tsk_fn = NULL;
+ mutex_unlock(&thread_mutex);
}
module_init(trace_event_init);