From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 20 May 2016 00:30:07 +0000 (-0400)
Subject: Fix: don't perform extra flush on metadata channel
X-Git-Tag: v2.6.6~3
X-Git-Url: https://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=7337bad8813e5d9ec7f37669afb3ec3bf07937da

Fix: don't perform extra flush on metadata channel

The metadata channel requires that the LTTng client layer and the ring
buffer keep a notion of the amount of data produced in the channel.

This issue has been introduced recently by commit
"Fix: flush empty packets on snapshot channel".

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/lib/ringbuffer/frontend_internal.h b/lib/ringbuffer/frontend_internal.h
index 47c08029..2bc54037 100644
--- a/lib/ringbuffer/frontend_internal.h
+++ b/lib/ringbuffer/frontend_internal.h
@@ -159,6 +159,9 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf,
 extern
 void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf);
 
+extern
+void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf);
+
 /* Buffer write helpers */
 
 static inline
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 708bc6d3..6eec3232 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -900,15 +900,6 @@ int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
 	unsigned long consumed_cur, write_offset;
 	int finalized;
 
-	/*
-	 * First, ensure we perform a "final" flush onto the stream.  This will
-	 * ensure we create a packet of padding if we encounter an empty
-	 * packet. This ensures the time-stamps right before the snapshot is
-	 * used as end of packet timestamp.
-	 */
-	if (!buf->quiescent)
-		_lib_ring_buffer_switch_remote(buf, SWITCH_FLUSH);
-
 retry:
 	finalized = ACCESS_ONCE(buf->finalized);
 	/*
@@ -1659,6 +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
diff --git a/lib/ringbuffer/ring_buffer_vfs.c b/lib/ringbuffer/ring_buffer_vfs.c
index 4389b5f6..71991ebb 100644
--- a/lib/ringbuffer/ring_buffer_vfs.c
+++ b/lib/ringbuffer/ring_buffer_vfs.c
@@ -191,6 +191,15 @@ long lib_ring_buffer_ioctl(struct file *filp, unsigned int cmd,
 
 	switch (cmd) {
 	case RING_BUFFER_SNAPSHOT:
+		/*
+		 * First, ensure we perform a "final" flush onto the
+		 * stream.  This will ensure we create a packet of
+		 * padding if we encounter an empty packet. This ensures
+		 * the time-stamps right before the snapshot is used as
+		 * end of packet timestamp.
+		 */
+		if (!buf->quiescent)
+			lib_ring_buffer_switch_remote_empty(buf);
 		return lib_ring_buffer_snapshot(buf, &buf->cons_snapshot,
 					    &buf->prod_snapshot);
 	case RING_BUFFER_SNAPSHOT_GET_CONSUMED:
@@ -320,6 +329,15 @@ long lib_ring_buffer_compat_ioctl(struct file *filp, unsigned int cmd,
 
 	switch (cmd) {
 	case RING_BUFFER_COMPAT_SNAPSHOT:
+		/*
+		 * First, ensure we perform a "final" flush onto the
+		 * stream.  This will ensure we create a packet of
+		 * padding if we encounter an empty packet. This ensures
+		 * the time-stamps right before the snapshot is used as
+		 * end of packet timestamp.
+		 */
+		if (!buf->quiescent)
+			lib_ring_buffer_switch_remote_empty(buf);
 		return lib_ring_buffer_snapshot(buf, &buf->cons_snapshot,
 						&buf->prod_snapshot);
 	case RING_BUFFER_COMPAT_SNAPSHOT_GET_CONSUMED:
diff --git a/lttng-abi.c b/lttng-abi.c
index 196aed84..0f01d3d7 100644
--- a/lttng-abi.c
+++ b/lttng-abi.c
@@ -629,6 +629,18 @@ long lttng_metadata_ring_buffer_ioctl(struct file *filp,
 			goto err;
 		break;
 	}
+	case RING_BUFFER_SNAPSHOT:
+	{
+		/*
+		 * Force the buffer to quiescent so the ring buffer
+		 * don't attempt to perform a SWITCH_FLUSH, which would
+		 * desynchronize the client accounting of the amount of
+		 * data available in the buffer from the ring buffer
+		 * view.
+		 */
+		buf->quiescent = true;
+		break;
+	}
 	default:
 		break;
 	}
@@ -699,6 +711,18 @@ long lttng_metadata_ring_buffer_compat_ioctl(struct file *filp,
 			goto err;
 		break;
 	}
+	case RING_BUFFER_SNAPSHOT:
+	{
+		/*
+		 * Force the buffer to quiescent so the ring buffer
+		 * don't attempt to perform a SWITCH_FLUSH, which would
+		 * desynchronize the client accounting of the amount of
+		 * data available in the buffer from the ring buffer
+		 * view.
+		 */
+		buf->quiescent = true;
+		break;
+	}
 	default:
 		break;
 	}