Vold: Add the fstrim subsystem to vold

The fstrim subsystem implements the dotrim command, which goes
through all the writable filesystems on the device, and invokes
the FITRIM ioctl() on them.  This marks all the unused blocks on
the underlying flash device as unused, so the device performs better.

Change-Id: I5fc8c2f60e0bc823f162d0f89580fb288ecb2160
diff --git a/fstrim.h b/fstrim.h
new file mode 100644
index 0000000..e46e804
--- /dev/null
+++ b/fstrim.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+    int fstrim_filesystems(void);
+#ifdef __cplusplus
+}
+#endif
+