Android RecoverSystem 类

      昨天开会讨论IP网络升级时，需要一个后台服务做升级检测及下载数据，最后在定义下载的数据存放位置及如何做开机标志时，突然发现一个很好用的上层java类对象。


frameworks\base\core\java\android\os\RecoverySystem.java
那么这个类做了什么事情呢？又是如何做到的。

RecoverySystem类，可以帮助我们调用系统还原等操作：

android.os.RecoverySystem，提供了如下静态方法
  static void  installPackage(Context context, File packageFile)   //重启设备，安装一个更新包

  static void  rebootWipeUserData(Context context)  //重启设备，清除用户数据分区类似恢复出厂设置

  static String handleAftermath() 提供清除recover中相关文件，在开机广播中被调用

  static void  verifyPackage(File packageFile, RecoverySystem.ProgressListener listener, File deviceCertsZipFile)  //验证加密签名的系统更新包在安装前，其中第二个数接口的具体定义为 android.os.RecoverySystem.ProgressListener  其中只有一个回调方法  abstract void  onProgress(int progress)   来显示效验的进度。
  


下面具体看一下代码中是如何实现：
1、安装更新包：

    /**     * Reboots the device in order to install the given update     * package.     * Requires the {@link android.Manifest.permission#REBOOT} permission.     *     * @param context      the Context to use     * @param packageFile  the update package to install.  Must be on     * a partition mountable by recovery.  (The set of partitions     * known to recovery may vary from device to device.  Generally,     * /cache and /data are safe.)     *     * @throws IOException  if writing the recovery command file     * 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;        bootCommand(context, arg); // 都是调用了这个函数    }    /**     * 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);  // 写命令写入到recover中        try {            command.write(arg);            command.write("\n");        } finally {            command.close();        }        // Having written the command file, go ahead and reboot 系统重启        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);        pm.reboot("recovery");        throw new IOException("Reboot failed (no permissions?)");    }

2、出厂恢复

    /**     * 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.sendOrderedBroadcast(intent, 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");    }    /**     * 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");    }

3、验证签名
    public static void verifyPackage(File packageFile,
                                     ProgressListener listener,
                                     File deviceCertsZipFile)  请自行阅读源码

后面说一下重启 reboot 命令如何执行的：

无论是 factory reset 工厂恢复还是 安装更新包都会调用到reboot函数，调用   pm.reboot("recovery");

通到jni就是： android_os_Power.cpp

shutdown 调用 android_reboot(ANDROID_RB_POWEROFF, 0, 0);
reboot 调用 android_reboot(ANDROID_RB_RESTART2, 0, (char *) chars);
最终都是调用到下面函数：
int reboot (int  mode) 
{
    return __reboot( LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL );
}


＝＝＝＝＝linux kernel 内核流程＝＝＝＝＝
/bionic/libc/arch-arm/syscalls/__reboot.S
这个文件由gensyscalls.py自动产生，调用系统调用 __NR_reboot


bionic/libc/include/sys/linux-syscalls.h
#define __NR_reboot (__NR_SYSCALL_BASE+88)


/arch/arm/kernel/calls.S
__NR_reboot?就是系统函数sys_reboot


sys_reboot定义在./include/linux/syscalls.h，实现在./kernel/sys.c?sys_reboot会调用kernel_restart
最终kernel_restart调用每一个架构特定的machine_restart，即machine_restart执行每个架构特定的函数