tracing: Add disable_on_free option

Add a trace option to disable tracing on free. When this option is
set, a write into the free_buffer file will not only shrink the
ring buffer down to zero, but it will also disable tracing.

Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -425,6 +425,7 @@ static const char *trace_options[] = {
 	"graph-time",
 	"record-cmd",
 	"overwrite",
+	"disable_on_free",
 	NULL
 };
 
@@ -3518,7 +3519,8 @@ tracing_free_buffer_write(struct file *filp, const char __user *ubuf,
 static int
 tracing_free_buffer_release(struct inode *inode, struct file *filp)
 {
-	/* disable tracing */
+	/* disable tracing ? */
+	if (trace_flags & TRACE_ITER_STOP_ON_FREE)
 		tracing_off();
 	/* resize the ring buffer to 0 */
 	tracing_resize_ring_buffer(0);

kernel/trace/trace.h

@@ -609,6 +609,7 @@ enum trace_iterator_flags {
 	TRACE_ITER_GRAPH_TIME		= 0x80000,
 	TRACE_ITER_RECORD_CMD		= 0x100000,
 	TRACE_ITER_OVERWRITE		= 0x200000,
+	TRACE_ITER_STOP_ON_FREE		= 0x400000,
 };
 
 /*