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.

Signed-off-by: Mandeep Singh Baines <m...@chromium.org>
CC: Steven Rostedt <rost...@goodmis.org>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Ingo Molnar <mi...@redhat.com>
---
 kernel/trace/trace.c |    6 +++++-
 kernel/trace/trace.h |    1 +
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5c38c81..0b052da 100644
--- a/kernel/trace/trace.c
+++ b/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;
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 55e1f7f..3da9da0 100644
--- a/kernel/trace/trace.h
+++ b/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,
 };
 
 /*
-- 
1.7.8.6

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