verity: Implement verity tool

This allows for toggling block device verification at runtime.

Both A/B and non-A/B devices as well as VB1.0 and VB2.0 (AVB)
are supported.

Change-Id: If6bec67a000074804f71fa098ad46ba395cac635

verity_tool/main.cpp

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2018 The LineageOS 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 "verity_tool.h"
+
+#include <getopt.h>
+#include <stdio.h>
+#include <string.h>
+
+static void print_usage() {
+    printf("veritytool - toggle block device verification\n"
+           "    --help        show this help\n"
+           "    --enable      enable dm-verity\n"
+           "    --disable     disable dm-verity\n");
+}
+
+int main(int argc, char** argv) {
+    int c, rc;
+    int enable = 0;
+    bool flag_set = false;
+    struct option long_opts[] = {
+        {"disable", no_argument, &enable, 0},
+        {"enable", no_argument, &enable, 1},
+        {NULL, 0, NULL, 0},
+    };
+
+    while ((c = getopt_long(argc, argv, "de", long_opts, NULL)) != -1) {
+        switch (c) {
+            case 0:
+                flag_set = true;
+                break;
+            default:
+                print_usage();
+                exit(0);
+        }
+    }
+
+    if (!flag_set) {
+        print_usage();
+        exit(0);
+    }
+
+    if (!set_verity_enabled(enable)) {
+        printf("Error occurred in set_verity_enable\n");
+        exit(EXIT_FAILURE);
+    }
+
+    printf("Set verity mode to: %s\n", enable ? "enabled" : "disabled");
+    printf("Now reboot your device for settings to take effect\n");
+    return 0;
+}