libutils: add a system-wide tracing utility

This change adds some utility functionality for doing userland tracing
into the kernel trace log.

Change-Id: Id0a8cee9ea515b1d8765afd1cecf472a88b4b9e8

1 files changed, 47 insertions, 0 deletions

diff --git a/libs/utils/Trace.cpp b/libs/utils/Trace.cpp
new file mode 100644
index 0000000..c49278a
--- /dev/null
+++ b/libs/utils/Trace.cpp
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <cutils/properties.h>
+#include <utils/Log.h>
+#include <utils/Trace.h>
+
+namespace android {
+
+volatile int32_t Tracer::sIsReady = 0;
+int Tracer::sTraceFD = -1;
+uint64_t Tracer::sEnabledTags = 0;
+Mutex Tracer::sMutex;
+
+void Tracer::init() {
+    Mutex::Autolock lock(sMutex);
+
+    if (!sIsReady) {
+        const char* const traceFileName =
+                "/sys/kernel/debug/tracing/trace_marker";
+        sTraceFD = open(traceFileName, O_WRONLY);
+        if (sTraceFD == -1) {
+            ALOGE("error opening trace file: %s (%d)", strerror(errno), errno);
+        } else {
+            char value[PROPERTY_VALUE_MAX];
+            property_get("atrace.tags.enableflags", value, "0");
+            sEnabledTags = strtoll(value, NULL, 0) | ATRACE_TAG_ALWAYS;
+        }
+
+        android_atomic_release_store(1, &sIsReady);
+    }
+}
+
+} // namespace andoid