diff --git a/tools/ota/make-update-script.c b/tools/ota/make-update-script.c
new file mode 100644
index 0000000..225dc52
--- /dev/null
+++ b/tools/ota/make-update-script.c
@@ -0,0 +1,228 @@
+/*
+ * Copyright (C) 2008 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 "private/android_filesystem_config.h"
+
+#include <dirent.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/*
+ * Recursively walk the directory tree at <sysdir>/<subdir>, writing
+ * script commands to set permissions and create symlinks.
+ * Assume the contents already have the specified default permissions,
+ * so only output commands if they need to be changed from the defaults.
+ *
+ * Note that permissions are set by fs_config(), which uses a lookup table of
+ * Android permissions.  They are not drawn from the build host filesystem.
+ */
+static void walk_files(
+        const char *sysdir, const char *subdir,
+        unsigned default_uid, unsigned default_gid,
+        unsigned default_dir_mode, unsigned default_file_mode) {
+    const char *sep = strcmp(subdir, "") ? "/" : "";
+
+    char fn[PATH_MAX];
+    unsigned dir_uid = 0, dir_gid = 0, dir_mode = 0;
+    snprintf(fn, PATH_MAX, "system%s%s", sep, subdir);
+    fs_config(fn, 1, &dir_uid, &dir_gid, &dir_mode);
+
+    snprintf(fn, PATH_MAX, "%s%s%s", sysdir, sep, subdir);
+    DIR *dir = opendir(fn);
+    if (dir == NULL) {
+        perror(fn);
+        exit(1);
+    }
+
+    /*
+     * We can use "set_perm" and "set_perm_recursive" to set file permissions
+     * (owner, group, and file mode) for individual files and entire subtrees.
+     * We want to use set_perm_recursive efficiently to avoid setting the
+     * permissions of every single file in the system image individually.
+     *
+     * What we do is recursively set our entire subtree to the permissions
+     * used by the first file we encounter, and then use "set_perm" to adjust
+     * the permissions of subsequent files which don't match the first one.
+     * This is bad if the first file is an outlier, but it generally works.
+     * Subdirectories can do the same thing recursively if they're different.
+     */
+
+    int is_first = 1;
+    const struct dirent *e;
+    while ((e = readdir(dir))) {
+        // Skip over "." and ".." entries
+        if (!strcmp(e->d_name, ".") || !strcmp(e->d_name, "..")) continue;
+
+        if (e->d_type == DT_LNK) {  // Symlink
+
+            // Symlinks don't really have permissions, so this is orthogonal.
+            snprintf(fn, PATH_MAX, "%s/%s%s%s", sysdir, subdir, sep, e->d_name);
+            int len = readlink(fn, fn, PATH_MAX - 1);
+            if (len <= 0) {
+                perror(fn);
+                exit(1);
+            }
+            fn[len] = '\0';
+            printf("symlink %s SYSTEM:%s%s%s\n", fn, subdir, sep, e->d_name);
+
+        } else if (e->d_type == DT_DIR) {  // Subdirectory
+
+            // Use the parent directory as the model for default permissions.
+            // We haven't seen a file, so just make up some file defaults.
+            if (is_first && (
+                    dir_mode != default_dir_mode ||
+                    dir_uid != default_uid || dir_gid != default_gid)) {
+                default_uid = dir_uid;
+                default_gid = dir_gid;
+                default_dir_mode = dir_mode;
+                default_file_mode = dir_mode & default_file_mode & 0666;
+                printf("set_perm_recursive %d %d 0%o 0%o SYSTEM:%s\n",
+                         default_uid, default_gid,
+                         default_dir_mode, default_file_mode,
+                         subdir);
+            }
+
+            is_first = 0;
+
+            // Recursively handle the subdirectory.
+            // Note, the recursive call handles the directory's own permissions.
+            snprintf(fn, PATH_MAX, "%s%s%s", subdir, sep, e->d_name);
+            walk_files(sysdir, fn,
+                    default_uid, default_gid,
+                    default_dir_mode, default_file_mode);
+
+        } else {  // Ordinary file
+
+            // Get the file's desired permissions.
+            unsigned file_uid = 0, file_gid = 0, file_mode = 0;
+            snprintf(fn, PATH_MAX, "system/%s%s%s", subdir, sep, e->d_name);
+            fs_config(fn, 0, &file_uid, &file_gid, &file_mode);
+
+            // If this is the first file, its mode gets to become the default.
+            if (is_first && (
+                    dir_mode != default_dir_mode ||
+                    file_mode != default_file_mode ||
+                    dir_uid != default_uid || file_uid != default_uid ||
+                    dir_gid != default_gid || file_gid != default_gid)) {
+                default_uid = dir_uid;
+                default_gid = dir_gid;
+                default_dir_mode = dir_mode;
+                default_file_mode = file_mode;
+                printf("set_perm_recursive %d %d 0%o 0%o SYSTEM:%s\n",
+                         default_uid, default_gid,
+                         default_dir_mode, default_file_mode,
+                         subdir);
+            }
+
+            is_first = 0;
+
+            // Otherwise, override this file if it doesn't match the defaults.
+            if (file_mode != default_file_mode ||
+                file_uid != default_uid || file_gid != default_gid) {
+                printf("set_perm %d %d 0%o SYSTEM:%s%s%s\n",
+                         file_uid, file_gid, file_mode,
+                         subdir, sep, e->d_name);
+            }
+
+        }
+    }
+
+    // Set the directory's permissions directly, if they never got set.
+    if (dir_mode != default_dir_mode ||
+        dir_uid != default_uid || dir_gid != default_gid) {
+        printf("set_perm %d %d 0%o SYSTEM:%s\n",
+                dir_uid, dir_gid, dir_mode, subdir);
+    }
+
+    closedir(dir);
+}
+
+/*
+ * Generate the update script (in "Amend", see commands/recovery/commands.c)
+ * for the complete-reinstall OTA update packages the build system makes.
+ *
+ * The generated script makes a variety of sanity checks about the device,
+ * erases and reinstalls system files, and sets file permissions appropriately.
+ */
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+        fprintf(stderr, "usage: %s systemdir android-info.txt >update-script\n",
+                argv[0]);
+        return 2;
+    }
+
+    // ensure basic recovery script language compatibility
+    printf("assert compatible_with(\"0.2\") == \"true\"\n");
+
+    // if known, make sure the device name is correct
+    const char *device = getenv("TARGET_DEVICE");
+    if (device != NULL) {
+        printf("assert getprop(\"ro.product.device\") == \"%s\" || "
+                "getprop(\"ro.build.product\") == \"%s\"\n", device, device);
+    }
+
+    // scan android-info.txt to enforce compatibility with the target system
+    FILE *fp = fopen(argv[2], "r");
+    if (fp == NULL) {
+        perror(argv[2]);
+        return 1;
+    }
+
+    // The lines we're looking for look like:
+    //     version-bootloader=x.yy.zzzz
+    // or:
+    //     require version-bootloader=x.yy.zzzz
+    char line[256];
+    while (fgets(line, sizeof(line), fp)) {
+        const char *name = strtok(line, "="), *value = strtok(NULL, "\n");
+        if (value != NULL &&
+            (!strcmp(name, "version-bootloader") ||
+             !strcmp(name, "require version-bootloader"))) {
+            printf("assert getprop(\"ro.bootloader\") == \"%s\"\n", value);
+        }
+        // We also used to check version-baseband, but we update radio.img
+        // ourselves, so there's no need.
+    }
+
+    // erase the boot sector first, so if the update gets interrupted,
+    // the system will reboot into the recovery partition and start over.
+    printf("format BOOT:\n");
+
+    // write the radio image (actually just loads it into RAM for now)
+    printf("show_progress 0.1 0\n");
+    printf("write_radio_image PACKAGE:radio.img\n");
+
+    // erase and reinstall the system image
+    printf("show_progress 0.5 0\n");
+    printf("format SYSTEM:\n");
+    printf("copy_dir PACKAGE:system SYSTEM:\n");
+
+    // walk the files in the system image, set their permissions, etc.
+    // use -1 for default values to force permissions to be set explicitly.
+    walk_files(argv[1], "", -1, -1, -1, -1);
+
+    // as the last step, write the boot sector.
+    printf("show_progress 0.2 0\n");
+    printf("write_raw_image PACKAGE:boot.img BOOT:\n");
+
+    // after the end of the script, the radio will be written to cache
+    // leave some space in the progress bar for this operation
+    printf("show_progress 0.2 10\n");
+    return 0;
+}