tracing: Add an option for disabling markers

In our application, we have trace markers spread through user-space.
We have markers in GL, X, etc. These are super handy for Chrome's
about:tracing feature (Chrome + system + kernel trace view), but
can be very distracting when you're trying to debug a kernel issue.

I normally, use "grep -v tracing_mark_write" but it would be nice
if I could just temporarily disable markers all together.

Link: http://lkml.kernel.org/r/1347066739-26285-1-git-send-email-msb@chromium.org

CC: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -328,7 +328,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
 	TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
 	TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
-	TRACE_ITER_IRQ_INFO;
+	TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS;
 
 static int trace_stop_count;
 static DEFINE_RAW_SPINLOCK(tracing_start_lock);
@@ -470,6 +470,7 @@ static const char *trace_options[] = {
 	"overwrite",
 	"disable_on_free",
 	"irq-info",
+	"markers",
 	NULL
 };
 
@@ -3886,6 +3887,9 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 	if (tracing_disabled)
 		return -EINVAL;
 
+	if (!(trace_flags & TRACE_ITER_MARKERS))
+		return -EINVAL;
+
 	if (cnt > TRACE_BUF_SIZE)
 		cnt = TRACE_BUF_SIZE;
 

kernel/trace/trace.h

@@ -680,6 +680,7 @@ enum trace_iterator_flags {
 	TRACE_ITER_OVERWRITE		= 0x200000,
 	TRACE_ITER_STOP_ON_FREE		= 0x400000,
 	TRACE_ITER_IRQ_INFO		= 0x800000,
+	TRACE_ITER_MARKERS		= 0x1000000,
 };
 
 /*