X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=lib%2Fringbuffer%2Fring_buffer_frontend.c;h=6eec323232b8d2910b19603d82bbd47c2735f011;hb=7337bad8813e5d9ec7f37669afb3ec3bf07937da;hp=42cf317a01d56482ae07401b8d1d8123b332a1d5;hpb=b63af41cb645dcf8513e997714e47fafcb4492b4;p=lttng-modules.git

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 42cf317a..6eec3232 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1289,7 +1289,8 @@ 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 lib_ring_buffer *buf,
@@ -1480,12 +1481,14 @@ 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;
@@ -1647,6 +1650,13 @@ void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote);
 
+/* Switch sub-buffer even if current sub-buffer is empty. */
+void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf)
+{
+	_lib_ring_buffer_switch_remote(buf, SWITCH_FLUSH);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty);
+
 /*
  * Returns :
  * 0 if ok