6 files changed, 127 insertions, 0 deletions
diff --git a/src/lib/trace/.may_include b/src/lib/trace/.may_include
new file mode 100644
index 0000000000..45cd13676b
--- /dev/null
+++ b/src/lib/trace/.may_include
@@ -0,0 +1,3 @@
+orconfig.h
+lib/log/*.h
+lib/trace/*.h
diff --git a/src/lib/trace/debug.h b/src/lib/trace/debug.h
new file mode 100644
index 0000000000..e35616cf50
--- /dev/null
+++ b/src/lib/trace/debug.h
@@ -0,0 +1,30 @@
+/* Copyright (c) 2017-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file debug.h
+ * \brief Macros for debugging our event-trace support.
+ **/
+
+#ifndef TOR_TRACE_LOG_DEBUG_H
+#define TOR_TRACE_LOG_DEBUG_H
+
+#include "lib/log/log.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 */
diff --git a/src/lib/trace/events.h b/src/lib/trace/events.h
new file mode 100644
index 0000000000..1e1e7b9d16
--- /dev/null
+++ b/src/lib/trace/events.h
@@ -0,0 +1,45 @@
+/* Copyright (c) 2017-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file events.h
+ * \brief Header file for Tor event tracing.
+ **/
+
+#ifndef TOR_TRACE_EVENTS_H
+#define TOR_TRACE_EVENTS_H
+
+/*
+ * The following defines a generic event tracing function name that has to be
+ * used to trace events in the code base.
+ *
+ * That generic function is then defined by a event tracing framework. For
+ * instance, the "log debug" framework sends all trace events to log_debug()
+ * which is defined in src/trace/debug.h which can only be enabled at compile
+ * time (--enable-event-tracing-debug).
+ *
+ * By default, every trace events in the code base are replaced by a NOP. See
+ * doc/HACKING/Tracing.md for more information on how to use event tracing or
+ * add events.
+ */
+
+#ifdef TOR_EVENT_TRACING_ENABLED
+/* Map every trace event to a per subsystem macro. */
+#define tor_trace(subsystem, name, ...) \
+  tor_trace_##subsystem(name, __VA_ARGS__)
+
+/* Enable event tracing for the debug framework where all trace events are
+ * mapped to a log_debug(). */
+#ifdef USE_EVENT_TRACING_DEBUG
+#include "lib/trace/debug.h"
+#endif
+
+#else /* TOR_EVENT_TRACING_ENABLED */
+
+/* Reaching this point, we NOP every event declaration because event tracing
+ * is not been enabled at compile time. */
+#define tor_trace(subsystem, name, args...)
+
+#endif /* TOR_EVENT_TRACING_ENABLED */
+
+#endif /* TOR_TRACE_EVENTS_H */
diff --git a/src/lib/trace/include.am b/src/lib/trace/include.am
new file mode 100644
index 0000000000..6f10c98744
--- /dev/null
+++ b/src/lib/trace/include.am
@@ -0,0 +1,18 @@
+
+noinst_LIBRARIES += \
+	src/lib/libtor-trace.a
+
+TRACEHEADERS = \
+	src/lib/trace/trace.h \
+	src/lib/trace/events.h
+
+if USE_EVENT_TRACING_DEBUG
+TRACEHEADERS += \
+	src/lib/trace/debug.h
+endif
+
+# Library source files.
+src_lib_libtor_trace_a_SOURCES = \
+	src/lib/trace/trace.c
+
+noinst_HEADERS+= $(TRACEHEADERS)
diff --git a/src/lib/trace/trace.c b/src/lib/trace/trace.c
new file mode 100644
index 0000000000..18be63c5a8
--- /dev/null
+++ b/src/lib/trace/trace.c
@@ -0,0 +1,17 @@
+/* Copyright (c) 2017-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file trace.c
+ * \brief Common functions for event-tracing implementation
+ *
+ * See trace.h and doc/HACKING/Tracing.md for more information.
+ **/
+
+#include "lib/trace/trace.h"
+
+/** Initialize the tracing library. */
+void
+tor_trace_init(void)
+{
+}
diff --git a/src/lib/trace/trace.h b/src/lib/trace/trace.h
new file mode 100644
index 0000000000..606d435568
--- /dev/null
+++ b/src/lib/trace/trace.h
@@ -0,0 +1,14 @@
+/* Copyright (c) 2017-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file trace.h
+ * \brief Header for trace.c
+ **/
+
+#ifndef TOR_TRACE_TRACE_H
+#define TOR_TRACE_TRACE_H
+
+void tor_trace_init(void);
+
+#endif // TOR_TRACE_TRACE_H