From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 19 Nov 2021 16:08:15 +0000 (-0500)
Subject: relayd: clarify viewer_get_next_index no rotation condition
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=bb1dcf019b7b1c2057cc34afde9172d12fc3981e;p=lttng-tools.git

relayd: clarify viewer_get_next_index no rotation condition

The condition identifying cases where a viewer_get_next_index must not
perform a viewer stream rotation is relatively tricky to comprehend.

Split it in two intermediate variables, and use those variables to
print debugging statements when conditions for not performing a
rotation match.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ieca2fbf879c8ed45c0b3aa6035ac32679b12dcdc
---

diff --git a/src/bin/lttng-relayd/live.cpp b/src/bin/lttng-relayd/live.cpp
index 9cdc1c8d7..96ec11efc 100644
--- a/src/bin/lttng-relayd/live.cpp
+++ b/src/bin/lttng-relayd/live.cpp
@@ -29,6 +29,7 @@
 #include <urcu/futex.h>
 #include <urcu/rculist.h>
 #include <urcu/uatomic.h>
+#include <string>
 
 #include <common/common.h>
 #include <common/compat/endian.h>
@@ -1602,6 +1603,9 @@ int viewer_get_next_index(struct relay_connection *conn)
 	struct relay_stream *rstream = NULL;
 	struct ctf_trace *ctf_trace = NULL;
 	struct relay_viewer_stream *metadata_viewer_stream = NULL;
+	bool viewer_stream_and_session_in_same_chunk, viewer_stream_one_rotation_behind;
+	uint64_t stream_file_chunk_id = -1ULL, viewer_session_chunk_id = -1ULL;
+	enum lttng_trace_chunk_status status;
 
 	LTTNG_ASSERT(conn);
 
@@ -1682,12 +1686,50 @@ int viewer_get_next_index(struct relay_connection *conn)
 	 * This allows clients to consume all the packets of a trace chunk
 	 * after a session's destruction.
 	 */
-	if (!lttng_trace_chunk_ids_equal(conn->viewer_session->current_trace_chunk, vstream->stream_file.trace_chunk) &&
-			!(rstream->completed_rotation_count == vstream->last_seen_rotation_count + 1 && !rstream->trace_chunk)) {
-		DBG("Viewer session and viewer stream chunk IDs differ: "
-				"vsession chunk %p vstream chunk %p",
+	if (vstream->stream_file.trace_chunk) {
+		status = lttng_trace_chunk_get_id(
+				vstream->stream_file.trace_chunk,
+				&stream_file_chunk_id);
+		LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
+	}
+	if (conn->viewer_session->current_trace_chunk) {
+		status = lttng_trace_chunk_get_id(
 				conn->viewer_session->current_trace_chunk,
-				vstream->stream_file.trace_chunk);
+				&viewer_session_chunk_id);
+		LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
+	}
+
+	viewer_stream_and_session_in_same_chunk = lttng_trace_chunk_ids_equal(
+			conn->viewer_session->current_trace_chunk,
+			vstream->stream_file.trace_chunk);
+	viewer_stream_one_rotation_behind = rstream->completed_rotation_count ==
+			vstream->last_seen_rotation_count + 1;
+
+	if (viewer_stream_and_session_in_same_chunk) {
+		DBG("Transition to latest chunk check (%s -> %s): Same chunk, no need to rotate",
+				vstream->stream_file.trace_chunk ?
+						std::to_string(stream_file_chunk_id).c_str() :
+						"None",
+				conn->viewer_session->current_trace_chunk ?
+						std::to_string(viewer_session_chunk_id).c_str() :
+						"None");
+	} else if (viewer_stream_one_rotation_behind && !rstream->trace_chunk) {
+		DBG("Transition to latest chunk check (%s -> %s): One chunk behind relay stream which is being destroyed, no need to rotate",
+				vstream->stream_file.trace_chunk ?
+						std::to_string(stream_file_chunk_id).c_str() :
+						"None",
+				conn->viewer_session->current_trace_chunk ?
+						std::to_string(viewer_session_chunk_id).c_str() :
+						"None");
+	} else {
+		DBG("Transition to latest chunk check (%s -> %s): Viewer stream chunk ID and viewer session chunk ID differ, rotating viewer stream",
+				vstream->stream_file.trace_chunk ?
+						std::to_string(stream_file_chunk_id).c_str() :
+						"None",
+				conn->viewer_session->current_trace_chunk ?
+						std::to_string(viewer_session_chunk_id).c_str() :
+						"None");
+
 		viewer_stream_rotate_to_trace_chunk(vstream,
 				conn->viewer_session->current_trace_chunk);
 		vstream->last_seen_rotation_count =
@@ -1732,7 +1774,6 @@ int viewer_get_next_index(struct relay_connection *conn)
 	 */
 	if (!vstream->stream_file.handle) {
 		char file_path[LTTNG_PATH_MAX];
-		enum lttng_trace_chunk_status status;
 		struct fs_handle *fs_handle;
 
 		ret = utils_stream_file_path(rstream->path_name,