ftrace: add nop tracer

A no-op tracer which can serve two purposes:

 1. A template for development of a new tracer.
 2. A convenient way to see ftrace_printk() calls without
    an irrelevant trace making the output messy.

[ mingo@elte.hu: resolved conflicts ]
Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 65 insertions, 0 deletions

diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
new file mode 100644
index 000000000000..dafaefb84038
--- /dev/null
+++ b/kernel/trace/trace_nop.c
@@ -0,0 +1,65 @@
+/*
+ * nop tracer
+ *
+ * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <linux/ftrace.h>
+
+#include "trace.h"
+
+static struct trace_array       *ctx_trace;
+
+static void start_nop_trace(struct trace_array *tr)
+{
+        /* Nothing to do! */
+}
+
+static void stop_nop_trace(struct trace_array *tr)
+{
+        /* Nothing to do! */
+}
+
+static void nop_trace_init(struct trace_array *tr)
+{
+        ctx_trace = tr;
+
+        if (tr->ctrl)
+                start_nop_trace(tr);
+}
+
+static void nop_trace_reset(struct trace_array *tr)
+{
+        if (tr->ctrl)
+                stop_nop_trace(tr);
+}
+
+static void nop_trace_ctrl_update(struct trace_array *tr)
+{
+        /* When starting a new trace, reset the buffers */
+        if (tr->ctrl)
+                start_nop_trace(tr);
+        else
+                stop_nop_trace(tr);
+}
+
+static struct tracer nop_trace __read_mostly =
+{
+        .name           = "nop",
+        .init           = nop_trace_init,
+        .reset          = nop_trace_reset,
+        .ctrl_update    = nop_trace_ctrl_update,
+#ifdef CONFIG_FTRACE_SELFTEST
+        .selftest       = trace_selftest_startup_nop,
+#endif
+};
+
+__init static int init_nop_trace(void)
+{
+        return register_tracer(&nop_trace);
+}
+device_initcall(init_nop_trace);