X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=libringbuffer%2Fring_buffer_frontend.c;h=908539a8663973fde0a8e51384907b4690b0e30d;hb=77d7fa989f79f3c2cb14d26576cbbb54b0637594;hp=ed60d7e22aa63ee127f2ae8b00f186522bdaae13;hpb=a33eb425f64228f7e2e545cb2a9d8840720657ae;p=lttng-ust.git

diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index ed60d7e2..908539a8 100644
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -1488,7 +1488,8 @@ 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,
@@ -1662,12 +1663,14 @@ 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;