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