Documentation: ring buffer: SWITCH_FLUSH can be used when active

[lttng-ust.git] / libringbuffer / ring_buffer_frontend.c

diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index c7394b1fd668d6e307e251221fcb1d79df07fb9e..43496254ce443baaace6dd910bd89938edc30398 100644 (file)
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -642,7 +642,7 @@ void lib_ring_buffer_channel_switch_timer_start(struct channel *chan)
        }
 
        its.it_value.tv_sec = chan->switch_timer_interval / 1000000;
-       its.it_value.tv_nsec = chan->switch_timer_interval % 1000000;
+       its.it_value.tv_nsec = (chan->switch_timer_interval % 1000000) * 1000;
        its.it_interval.tv_sec = its.it_value.tv_sec;
        its.it_interval.tv_nsec = its.it_value.tv_nsec;
 
@@ -696,7 +696,7 @@ void lib_ring_buffer_channel_read_timer_start(struct channel *chan)
        }
 
        its.it_value.tv_sec = chan->read_timer_interval / 1000000;
-       its.it_value.tv_nsec = chan->read_timer_interval % 1000000;
+       its.it_value.tv_nsec = (chan->read_timer_interval % 1000000) * 1000;
        its.it_interval.tv_sec = its.it_value.tv_sec;
        its.it_interval.tv_nsec = its.it_value.tv_nsec;
 
@@ -1492,7 +1492,8 @@ void lib_ring_buffer_print_errors(struct channel *chan,
 /*
  * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
  *
- * Only executed when the buffer is finalized, in SWITCH_FLUSH.
+ * Only executed by SWITCH_FLUSH, which can be issued while tracing is
+ * active or at buffer finalization (destroy).
  */
 static
 void lib_ring_buffer_switch_old_start(struct lttng_ust_lib_ring_buffer *buf,
@@ -1666,12 +1667,14 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
                unsigned long sb_index, commit_count;
 
                /*
-                * We are performing a SWITCH_FLUSH. At this stage, there are no
-                * concurrent writes into the buffer.
+                * We are performing a SWITCH_FLUSH. There may be concurrent
+                * writes into the buffer if e.g. invoked while performing a
+                * snapshot on an active trace.
                 *
-                * The client does not save any header information.  Don't
-                * switch empty subbuffer on finalize, because it is invalid to
-                * deliver a completely empty subbuffer.
+                * If the client does not save any header information
+                * (sub-buffer header size == 0), don't switch empty subbuffer
+                * on finalize, because it is invalid to deliver a completely
+                * empty subbuffer.
                 */
                if (!config->cb.subbuffer_header_size())
                        return -1;