libcamera: tracing: Implement tracing infrastructure

Implement tracing infrastructure in libcamera. It takes .tp files, as
required by lttng, and generates a tracepoint header and C file, as lttng
requires. meson is updated accordingly to get it to compile with the
rest of libcamera. Update the documentation accordingly.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/meson.build

@@ -55,6 +55,7 @@ libcamera_sources = files([
 ])
 
 libcamera_sources += libcamera_public_headers
+libcamera_sources += libcamera_tracepoint_header
 
 includes = [
     libcamera_includes,
@@ -72,6 +73,11 @@ if libgnutls.found()
     config_h.set('HAVE_GNUTLS', 1)
 endif
 
+if liblttng.found()
+    config_h.set('HAVE_TRACING', 1)
+    libcamera_sources += files(['tracepoints.cpp'])
+endif
+
 if libudev.found()
     config_h.set('HAVE_LIBUDEV', 1)
     libcamera_sources += files([
@@ -114,6 +120,7 @@ libcamera_deps = [
     libatomic,
     libdl,
     libgnutls,
+    liblttng,
     libudev,
     dependency('threads'),
 ]

src/libcamera/tracepoints.cpp

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * tracepoints.cpp - Tracepoints with lttng
+ */
+#define TRACEPOINT_CREATE_PROBES
+#define TRACEPOINT_DEFINE
+
+#include "libcamera/internal/tracepoints.h"