概要

本文描述Android应用层要进入recovery模式时，需要设定参数的方式、以及参数的格式。

应用层的调用场景

有如下的场景需要让手机重启进入recovery模式：

系统升级；
恢复出厂设置

RecoverySystem.java

// \frameworks\base\core\java\android\os\RecoverySystem.java * fails, or if the reboot itself fails. */public static void installPackage(Context context, File packageFile)    throws IOException {    String filename = packageFile.getCanonicalPath();    Log.w(TAG, "!!! REBOOTING TO INSTALL " + filename + " !!!");    String arg = "--update_package=" + filename +        "\n--locale=" + Locale.getDefault().toString();    bootCommand(context, arg);}/** * Reboots the device and wipes the user data partition.  This is * sometimes called a "factory reset", which is something of a * misnomer because the system partition is not restored to its * factory state. * Requires the {@link android.Manifest.permission#REBOOT} permission. * * @param context  the Context to use * * @throws IOException  if writing the recovery command file * fails, or if the reboot itself fails. */public static void rebootWipeUserData(Context context) throws IOException {    final ConditionVariable condition = new ConditionVariable();    Intent intent = new Intent("android.intent.action.MASTER_CLEAR_NOTIFICATION");    context.sendOrderedBroadcastAsUser(intent, UserHandle.OWNER,            android.Manifest.permission.MASTER_CLEAR,            new BroadcastReceiver() {                @Override                public void onReceive(Context context, Intent intent) {                    condition.open();                }            }, null, 0, null, null);    // Block until the ordered broadcast has completed.    condition.block();    bootCommand(context, "--wipe_data\n--locale=" + Locale.getDefault().toString());}/** * Reboot into the recovery system to wipe the /cache partition. * @throws IOException if something goes wrong. */public static void rebootWipeCache(Context context) throws IOException {    bootCommand(context, "--wipe_cache\n--locale=" + Locale.getDefault().toString());}/** * Reboot into the recovery system with the supplied argument. * @param arg to pass to the recovery utility. * @throws IOException if something goes wrong. */private static void bootCommand(Context context, String arg) throws IOException {    RECOVERY_DIR.mkdirs();  // In case we need it    COMMAND_FILE.delete();  // In case it's not writable    LOG_FILE.delete();    FileWriter command = new FileWriter(COMMAND_FILE);    try {        command.write(arg);        command.write("\n");    } finally {        command.close();    }    // Having written the command file, go ahead and reboot    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);    pm.reboot("recovery");    throw new IOException("Reboot failed (no permissions?)");}

这里包括了：

installPackage：系统升级，比如FOTA、组合按键进入recovery，等等
rebootWipeUserData：重启用于擦除用户数据（恢复出厂设置）；
rebootWipeCache：擦除cache分区

所有这些都通过COMMAND_FILE（/cache/recovery/command）文件来给recovery传递命令行参数。

command文件的格式

如同上面代码所描述的，command文件中，每个参数占用一行；每个参数本身采用--parName=parValue的格式。如：

--wipe_data--locale=en

因为Android底层是Linux，所以换行使用的是\n，而不是\r\n。——参考上面的java代码。当然，recovery为了提高可靠性，增加了容错处理。下面是recovery.cpp中的处理过程：

// \bootable\recovery\recovery.cpp// --- if that doesn't work, try the command fileif (*argc <= 1) {    FILE *fp = fopen_path(COMMAND_FILE, "r");    if (fp != NULL) {        char *token;        char *argv0 = (*argv)[0];        *argv = (char **) malloc(sizeof(char *) * MAX_ARGS);        (*argv)[0] = argv0;  // use the same program name        char buf[MAX_ARG_LENGTH];        for (*argc = 1; *argc < MAX_ARGS; ++*argc) {            if (!fgets(buf, sizeof(buf), fp)) break;            token = strtok(buf, "\r\n");            if (token != NULL) {                (*argv)[*argc] = strdup(token);  // Strip newline.            } else {                --*argc;            }        }        check_and_fclose(fp, COMMAND_FILE);        LOGI("Got arguments from %s\n", COMMAND_FILE);    }}

recovery支持的命令行参数

recovery支持的参数由recovery.cpp中的OPTIONS来定义：

static const struct option OPTIONS[] = {  { "send_intent", required_argument, NULL, 's' },  { "update_package", required_argument, NULL, 'u' },  { "wipe_data", no_argument, NULL, 'w' },  { "wipe_cache", no_argument, NULL, 'c' },  { "show_text", no_argument, NULL, 't' },  { "just_exit", no_argument, NULL, 'x' },  { "locale", required_argument, NULL, 'l' },  { NULL, 0, NULL, 0 },};

事实上，各个厂商可以根据需求而进行扩展，只要recovery和上层应用保持一致即可。——在Recovery模式下的文本显示一文中讲到了locale的注意事项，如前面Java代码给出的，传入的是Locale.toString()，而不是Locale.getLanguage()。

BCB (Bootloader Control Block)

待补充

接下来分析应用层如何进入recovery模式的，包括ShutdownThread.java、android_reboot.c等的分析。

Recovery模式的命令行参数

概要

应用层的调用场景

RecoverySystem.java

command文件的格式

recovery支持的命令行参数

BCB (Bootloader Control Block)

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