tracing/ring-buffer: Only have tracing_on disable tracing buffers

As the ring-buffer code is being used by other facilities in the
kernel, having tracing_on file disable *all* buffers is not a desired
affect. It should only disable the ftrace buffers that are being used.

Move the code into the trace.c file and use the buffer disabling
for tracing_on() and tracing_off(). This way only the ftrace buffers
will be affected by them and other kernel utilities will not be
confused to why their output suddenly stopped.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 107 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 10d5503f0d04..f3c13d63d064 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -352,6 +352,59 @@ static void wakeup_work_handler(struct work_struct *work)
 static DECLARE_DELAYED_WORK(wakeup_work, wakeup_work_handler);
 
 /**
+ * tracing_on - enable tracing buffers
+ *
+ * This function enables tracing buffers that may have been
+ * disabled with tracing_off.
+ */
+void tracing_on(void)
+{
+	if (global_trace.buffer)
+		ring_buffer_record_on(global_trace.buffer);
+	/*
+	 * This flag is only looked at when buffers haven't been
+	 * allocated yet. We don't really care about the race
+	 * between setting this flag and actually turning
+	 * on the buffer.
+	 */
+	global_trace.buffer_disabled = 0;
+}
+EXPORT_SYMBOL_GPL(tracing_on);
+
+/**
+ * tracing_off - turn off tracing buffers
+ *
+ * This function stops the tracing buffers from recording data.
+ * It does not disable any overhead the tracers themselves may
+ * be causing. This function simply causes all recording to
+ * the ring buffers to fail.
+ */
+void tracing_off(void)
+{
+	if (global_trace.buffer)
+		ring_buffer_record_on(global_trace.buffer);
+	/*
+	 * This flag is only looked at when buffers haven't been
+	 * allocated yet. We don't really care about the race
+	 * between setting this flag and actually turning
+	 * on the buffer.
+	 */
+	global_trace.buffer_disabled = 1;
+}
+EXPORT_SYMBOL_GPL(tracing_off);
+
+/**
+ * tracing_is_on - show state of ring buffers enabled
+ */
+int tracing_is_on(void)
+{
+	if (global_trace.buffer)
+		return ring_buffer_record_is_on(global_trace.buffer);
+	return !global_trace.buffer_disabled;
+}
+EXPORT_SYMBOL_GPL(tracing_is_on);
+
+/**
  * trace_wake_up - wake up tasks waiting for trace input
  *
  * Schedules a delayed work to wake up any task that is blocked on the
@@ -4567,6 +4620,55 @@ static __init void create_trace_options_dir(void)
 		create_trace_option_core_file(trace_options[i], i);
 }
 
+static ssize_t
+rb_simple_read(struct file *filp, char __user *ubuf,
+	       size_t cnt, loff_t *ppos)
+{
+	struct ring_buffer *buffer = filp->private_data;
+	char buf[64];
+	int r;
+
+	if (buffer)
+		r = ring_buffer_record_is_on(buffer);
+	else
+		r = 0;
+
+	r = sprintf(buf, "%d\n", r);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+rb_simple_write(struct file *filp, const char __user *ubuf,
+		size_t cnt, loff_t *ppos)
+{
+	struct ring_buffer *buffer = filp->private_data;
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	if (buffer) {
+		if (val)
+			ring_buffer_record_on(buffer);
+		else
+			ring_buffer_record_off(buffer);
+	}
+
+	(*ppos)++;
+
+	return cnt;
+}
+
+static const struct file_operations rb_simple_fops = {
+	.open		= tracing_open_generic,
+	.read		= rb_simple_read,
+	.write		= rb_simple_write,
+	.llseek		= default_llseek,
+};
+
 static __init int tracer_init_debugfs(void)
 {
 	struct dentry *d_tracer;
@@ -4626,6 +4728,9 @@ static __init int tracer_init_debugfs(void)
 	trace_create_file("trace_clock", 0644, d_tracer, NULL,
 			  &trace_clock_fops);
 
+	trace_create_file("tracing_on", 0644, d_tracer,
+			    global_trace.buffer, &rb_simple_fops);
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 	trace_create_file("dyn_ftrace_total_info", 0444, d_tracer,
 			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
@@ -4863,6 +4968,8 @@ __init static int tracer_alloc_buffers(void)
 		goto out_free_cpumask;
 	}
 	global_trace.entries = ring_buffer_size(global_trace.buffer);
+	if (global_trace.buffer_disabled)
+		tracing_off();
 
 
 #ifdef CONFIG_TRACER_MAX_TRACE