[PATCH v2 04/13] tracing: Add tracer_tracing_disable/enable() functions

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Allow a tracer to disable writing to its buffer for a temporary amount of
time and re-enable it.

The tracer_tracing_disable() will disable writing to the trace array
buffer, and requires a tracer_tracing_enable() to re-enable it.

The difference between tracer_tracing_disable() and tracer_tracing_off()
is that the disable version can nest, and requires as many enable() calls
as disable() calls to re-enable the buffer. Where as the off() function
can be called multiple times and only requires a singe tracer_tracing_on()
to re-enable the buffer.

Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Daniel Thompson <danielt@kernel.org>
Cc: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 33 +++++++++++++++++++++++++++++++++
 kernel/trace/trace.h |  2 ++
 2 files changed, 35 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5b8db27fb6ef..e36b1244fa82 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1582,6 +1582,39 @@ void tracer_tracing_off(struct trace_array *tr)
 	smp_wmb();
 }
 
+/**
+ * tracer_tracing_disable() - temporary disable the buffer from write
+ * @tr: The trace array to disable its buffer for
+ *
+ * Expects trace_tracing_enable() to re-enable tracing.
+ * The difference between this and tracer_tracing_off() is that this
+ * is a counter and can nest, whereas, tracer_tracing_off() can
+ * be called multiple times and a single trace_tracing_on() will
+ * enable it.
+ */
+void tracer_tracing_disable(struct trace_array *tr)
+{
+	if (WARN_ON_ONCE(!tr->array_buffer.buffer))
+		return;
+
+	ring_buffer_record_disable(tr->array_buffer.buffer);
+}
+
+/**
+ * tracer_tracing_enable() - counter part of tracer_tracing_disable()
+ * @tr: The trace array that had tracer_tracincg_disable() called on it
+ *
+ * This is called after tracer_tracing_disable() has been called on @tr,
+ * when it's safe to re-enable tracing.
+ */
+void tracer_tracing_enable(struct trace_array *tr)
+{
+	if (WARN_ON_ONCE(!tr->array_buffer.buffer))
+		return;
+
+	ring_buffer_record_enable(tr->array_buffer.buffer);
+}
+
 /**
  * tracing_off - turn off tracing buffers
  *
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 79be1995db44..74f1fe5788d4 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -665,6 +665,8 @@ bool tracing_is_disabled(void);
 bool tracer_tracing_is_on(struct trace_array *tr);
 void tracer_tracing_on(struct trace_array *tr);
 void tracer_tracing_off(struct trace_array *tr);
+void tracer_tracing_disable(struct trace_array *tr);
+void tracer_tracing_enable(struct trace_array *tr);
 struct dentry *trace_create_file(const char *name,
 				 umode_t mode,
 				 struct dentry *parent,
-- 
2.47.2