tracing: poll-able ring_buffer consumer

index b81ceed..6fd2664 100644
@@ -4,6 +4,7 @@
 #include <linux/kmemcheck.h>
 #include <linux/mm.h>
 #include <linux/seq_file.h>
+#include <linux/poll.h>
 
 struct ring_buffer;
 struct ring_buffer_iter;

@@ -188,6 +189,8 @@ int ring_buffer_read_page(struct ring_buffer *buffer, void **data_page,
 void ring_buffer_notify(struct ring_buffer *buffer);
 signed long ring_buffer_wait_page(struct ring_buffer *buffer, int cpu,
 		signed long timeout);
+unsigned int ring_buffer_poll(struct ring_buffer *buffer, int cpu,
+		struct file *filp, poll_table *poll_table);
 
 struct trace_seq;
 

index db82b38..c7c23da 100644
@@ -3389,6 +3389,22 @@ ring_buffer_wait_page(struct ring_buffer *buffer, int cpu, signed long timeout)
 			rb_page_available(cpu_buffer), timeout);
 }
 
+unsigned int ring_buffer_poll(struct ring_buffer *buffer, int cpu,
+		struct file *filp, poll_table *poll_table)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+
+	if (rb_page_available(cpu_buffer))
+		return POLLIN | POLLRDNORM;
+
+	poll_wait(filp, &cpu_buffer->sleepers, poll_table);
+
+	if (rb_page_available(cpu_buffer))
+		return POLLIN | POLLRDNORM;
+
+	return 0;
+}
+
 /**
  * ring_buffer_size - return the size of the ring buffer (in bytes)
  * @buffer: The ring buffer.

index ee435ed..c2aa14c 100644
@@ -3294,6 +3294,14 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static
+unsigned int tracing_buffers_poll(struct file *filp, poll_table *poll_table)
+{
+	struct ftrace_buffer_info *info = filp->private_data;
+
+	return ring_buffer_poll(info->tr->buffer, info->cpu, filp, poll_table);
+}
+
 struct buffer_ref {
 	struct ring_buffer	*buffer;
 	void			*page;

@@ -3459,6 +3467,7 @@ static const struct file_operations tracing_buffers_fops = {
 	.open		= tracing_buffers_open,
 	.read		= tracing_buffers_read,
 	.release	= tracing_buffers_release,
+	.poll		= tracing_buffers_poll,
 	.splice_read	= tracing_buffers_splice_read,
 	.llseek		= no_llseek,
 };