feat(plugin): issue warning if trace clock is not monotonic

We don't know for sure which trace clock is used by LTTng US, but if the
trace.dat (ftrace) clock is not monotonic, it is likely that the traces
are misaligned. Issue a warning in this case, but proceed.

Signed-off-by: Felix Moessbauer <[email protected]>

Author: fmoessbauer

src/bt-ftrace-source.c

@@ -215,6 +215,9 @@ static void create_metadata_and_stream(bt_self_component *self_component,
 	char NAME_BUF[32];
 	const uint64_t mip_version =
 		bt_self_component_get_graph_mip_version(self_component);
+	/* assume monotonic clock if not provided otherwise */
+	const char *traceclock = "mono";
+	bt_bool clock_is_monotonic = true;
 
 	/* Create a default trace class */
 	bt_trace_class *trace_class = bt_trace_class_create(self_component);
@@ -223,10 +226,19 @@ static void create_metadata_and_stream(bt_self_component *self_component,
 	bt_stream_class *stream_class = bt_stream_class_create(trace_class);
 	bt_stream_class_set_name(stream_class, "ftrace-stream");
 
+#if WITH_TRACE_CMD_PRIVATE_SYMBOLS
+	traceclock = tracecmd_get_trace_clock(ftrace_in->tc_input);
+#endif
 	/* Create a default clock class (1 GHz frequency) */
 	bt_clock_class *clock_class = bt_clock_class_create(self_component);
-	bt_clock_class_set_name(clock_class, "monotonic");
-	bt_clock_class_set_description(clock_class, "Monotonic Clock");
+	if (strcmp(traceclock, "mono") == 0 ||
+		strcmp(traceclock, "mono_raw") == 0) {
+		bt_clock_class_set_name(clock_class, "monotonic");
+		bt_clock_class_set_description(clock_class, "Monotonic Clock");
+	} else {
+		clock_is_monotonic = false;
+		bt_clock_class_set_name(clock_class, traceclock);
+	}
 	/* make the clock compatible with an LTTng US clock definition */
 	if (ftrace_in->clock_offset_ns) {
 		bt_clock_class_set_offset(clock_class,
@@ -248,6 +260,12 @@ static void create_metadata_and_stream(bt_self_component *self_component,
 			bt_clock_class_set_uid(clock_class, ftrace_in->clock_uid);
 #endif
 		}
+		if (!clock_is_monotonic) {
+			BT_FTRACE_LOG_WARNING(
+				ftrace_in->log_level,
+				"ftrace used non-monotonic clock \"%s\". Traces are likely misaligned.",
+				traceclock);
+		}
 	}
 
 	/*

src/trace-cmd-private.h

@@ -11,5 +11,6 @@
 struct tracecmd_input;
 
 const char *tracecmd_get_uname(struct tracecmd_input *handle);
+const char *tracecmd_get_trace_clock(struct tracecmd_input *handle);
 
 #endif