ring-buffer: Add stats field for amount read from trace ring buffer

Add a stat about the number of events read from the ring buffer:

 #  cat /debug/tracing/per_cpu/cpu0/stats
entries: 39869
overrun: 870512
commit overrun: 0
bytes: 1449912
oldest event ts:  6561.368690
now ts:  6565.246426
dropped events: 0
read events: 112    <-- Added

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

2 files changed, 21 insertions, 0 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 13950d9027cb..7244acde77b0 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3103,6 +3103,24 @@ ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
 EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
 
 /**
+ * ring_buffer_read_events_cpu - get the number of events successfully read
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of events read
+ */
+unsigned long
+ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
+{
+        struct ring_buffer_per_cpu *cpu_buffer;
+
+        if (!cpumask_test_cpu(cpu, buffer->cpumask))
+                return 0;
+
+        cpu_buffer = buffer->buffers[cpu];
+        return cpu_buffer->read;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
+
+/**
  * ring_buffer_entries - get the number of entries in a buffer
  * @buffer: The ring buffer
  *
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d399592701aa..90a1c71fdbfc 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4430,6 +4430,9 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
         cnt = ring_buffer_dropped_events_cpu(tr->buffer, cpu);
         trace_seq_printf(s, "dropped events: %ld\n", cnt);
 
+        cnt = ring_buffer_read_events_cpu(tr->buffer, cpu);
+        trace_seq_printf(s, "read events: %ld\n", cnt);
+
         count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
 
         kfree(s);