From eca1eb92d894520ba01e6e00ead720c414eb68a8 Mon Sep 17 00:00:00 2001
From: Steven Noonan <steven@uplinklabs.net>
Date: Fri, 19 Sep 2008 03:06:43 -0700
Subject: [PATCH] --- yaml --- r: 116623 b: refs/heads/master c:
 fb1b6d8b5154c692172a424e45fbd0573295cb93 h: refs/heads/master i:   116621:
 040c07ddce9633efb09088c36ebb2f8623c9eff7   116619:
 0b44e6ecd804cb821139c75d3cccee39e24e46d2   116615:
 25ef4b41cb339e081dbaee26aba8e5a4abd92278   116607:
 f2c63ae7f3d17aaf95afa8ec2d7db890b3293b01 v: v3

---
 [refs]                              |  2 +-
 trunk/kernel/trace/Kconfig          | 10 +++++
 trunk/kernel/trace/Makefile         |  1 +
 trunk/kernel/trace/trace.h          |  4 ++
 trunk/kernel/trace/trace_nop.c      | 65 +++++++++++++++++++++++++++++
 trunk/kernel/trace/trace_selftest.c |  9 ++++
 6 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 trunk/kernel/trace/trace_nop.c

diff --git a/[refs] b/[refs]
index 68ad322641ef..a92617afca0f 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5bf9a1ee350a10feb94107de32a203d81fbbe706
+refs/heads/master: fb1b6d8b5154c692172a424e45fbd0573295cb93
diff --git a/trunk/kernel/trace/Kconfig b/trunk/kernel/trace/Kconfig
index 16e5bb5daaa5..d7b2de744631 100644
--- a/trunk/kernel/trace/Kconfig
+++ b/trunk/kernel/trace/Kconfig
@@ -101,6 +101,16 @@ config SCHED_TRACER
 	  This tracer tracks the latency of the highest priority task
 	  to be scheduled in, starting from the point it has woken up.
 
+config NOP_TRACER
+	bool "NOP Tracer"
+	depends on HAVE_FTRACE
+	depends on DEBUG_KERNEL
+	select TRACING
+	help
+	  This tracer does nothing. The primary purpose for it is to
+	  politely print the output of ftrace_printk() calls without
+	  the overhead of an irrelevant trace taking place.
+
 config CONTEXT_SWITCH_TRACER
 	bool "Trace process context switches"
 	depends on HAVE_FTRACE
diff --git a/trunk/kernel/trace/Makefile b/trunk/kernel/trace/Makefile
index 58ec61c44bd6..73ba13f5a461 100644
--- a/trunk/kernel/trace/Makefile
+++ b/trunk/kernel/trace/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_FTRACE) += trace_functions.o
 obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
+obj-$(CONFIG_NOP_TRACER) += trace_nop.o
 obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
 
diff --git a/trunk/kernel/trace/trace.h b/trunk/kernel/trace/trace.h
index 42f65d0097f0..447d4b9b6391 100644
--- a/trunk/kernel/trace/trace.h
+++ b/trunk/kernel/trace/trace.h
@@ -339,6 +339,10 @@ extern int trace_selftest_startup_preemptirqsoff(struct tracer *trace,
 extern int trace_selftest_startup_wakeup(struct tracer *trace,
 					 struct trace_array *tr);
 #endif
+#ifdef CONFIG_NOP_TRACER
+extern int trace_selftest_startup_nop(struct tracer *trace,
+					 struct trace_array *tr);
+#endif
 #ifdef CONFIG_CONTEXT_SWITCH_TRACER
 extern int trace_selftest_startup_sched_switch(struct tracer *trace,
 					       struct trace_array *tr);
diff --git a/trunk/kernel/trace/trace_nop.c b/trunk/kernel/trace/trace_nop.c
new file mode 100644
index 000000000000..dafaefb84038
--- /dev/null
+++ b/trunk/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);
diff --git a/trunk/kernel/trace/trace_selftest.c b/trunk/kernel/trace/trace_selftest.c
index 630715bbd572..82db9103b9bc 100644
--- a/trunk/kernel/trace/trace_selftest.c
+++ b/trunk/kernel/trace/trace_selftest.c
@@ -418,6 +418,15 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
 }
 #endif /* CONFIG_IRQSOFF_TRACER && CONFIG_PREEMPT_TRACER */
 
+#ifdef CONFIG_NOP_TRACER
+int
+trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
+{
+	/* What could possibly go wrong? */
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_SCHED_TRACER
 static int trace_wakeup_test_thread(void *data)
 {