trace: Add a basic event-tracing infrastructure.

This commit adds the src/trace directory containing the basics for our tracing
subsystem. It is not used in the code base. The "src/trace/debug.h" file
contains an example on how we can map our tor trace events to log_debug().

The tracing subsystem can only be enabled by tracing framework at compile
time. This commit introduces the "--enable-tracing-debug" option that will
make all "tor_trace()" function be maped to "log_debug()".

Closes #13802

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/trace/debug.h b/src/trace/debug.h
new file mode 100644
index 0000000000..3a1652543a
--- /dev/null
+++ b/src/trace/debug.h
@@ -0,0 +1,25 @@
+/* Copyright (c) 2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#ifndef TOR_TRACE_LOG_DEBUG_H
+#define TOR_TRACE_LOG_DEBUG_H
+
+#include "torlog.h"
+
+/* Stringify pre-processor trick. */
+#define XSTR(d) STR(d)
+#define STR(s) #s
+
+/* Send every event to a debug log level. This is useful to debug new trace
+ * events without implementing them for a specific event tracing framework.
+ * Note that the arguments are ignored since at this step we do not know the
+ * types and amount there is. */
+
+/* Example on how to map a tracepoint to log_debug(). */
+#undef tor_trace
+#define tor_trace(subsystem, name, args...) \
+  log_debug(LD_GENERAL, "Trace event \"" XSTR(name) "\" from " \
+                        "\"" XSTR(subsystem) "\" hit. " \
+                        "(line "XSTR(__LINE__) ")")
+
+#endif /* TOR_TRACE_LOG_DEBUG_H */