Android13 救援模式

救援模式：

目前市场上的手机消费者包括资深用户，当他们的手机出现无限循环启动的异常时，用户没有办法修复异常只能通过设备商售后处理。Google在Android 8.0加入该新功能，称之为rescue party救援程序。主要监控系统核心程序出现循环崩溃的时候，会启动该程序，根据不同的救援级别做出一系列操作，看是否可恢复设备，最严重的时候则是通过进入recovery然后提供用户清空用户数据恢复出厂设置解决。

遇到开机进到recovery模式的情况，其实我们全局搜索下关键字“RescueParty”

就可以看到在init进程收到reboot,recovery指令之前，就可以看到因为救援模式，而发生了wipe-data

以下代码基于Android13:

首先救援分不同的级别，不同的级别执行不同的代码逻辑

//QSSI.13\frameworks\base\services\core\java\com\android\server\RescueParty.java
@VisibleForTesting
static final int LEVEL_NONE = 0;
@VisibleForTesting
static final int LEVEL_RESET_SETTINGS_UNTRUSTED_DEFAULTS = 1;
@VisibleForTesting
static final int LEVEL_RESET_SETTINGS_UNTRUSTED_CHANGES = 2;
@VisibleForTesting
static final int LEVEL_RESET_SETTINGS_TRUSTED_DEFAULTS = 3;
@VisibleForTesting
static final int LEVEL_WARM_REBOOT = 4;
@VisibleForTesting
static final int LEVEL_FACTORY_RESET = 5;
@VisibleForTesting
static final String PROP_RESCUE_BOOT_COUNT = "sys.rescue_boot_count";
@VisibleForTesting
static final String TAG = "RescueParty";
....
private static void executeRescueLevelInternal(Context context, int level, @Nullable
        String failedPackage) throws Exception {
    FrameworkStatsLog.write(FrameworkStatsLog.RESCUE_PARTY_RESET_REPORTED, level);
    // Try our best to reset all settings possible, and once finished
    // rethrow any exception that we encountered
    Exception res = null;
    Runnable runnable;
    Thread thread;
    switch (level) {
        case LEVEL_RESET_SETTINGS_UNTRUSTED_DEFAULTS:
            try {
                resetAllSettingsIfNecessary(context, Settings.RESET_MODE_UNTRUSTED_DEFAULTS,
                        level);
            } catch (Exception e) {
                res = e;
            }
            try {
                resetDeviceConfig(context, /*isScoped=*/true, failedPackage);
            } catch (Exception e) {
                res = e;
            }
            break;
        case LEVEL_RESET_SETTINGS_UNTRUSTED_CHANGES:
            try {
                resetAllSettingsIfNecessary(context, Settings.RESET_MODE_UNTRUSTED_CHANGES,
                        level);
            } catch (Exception e) {
                res = e;
            }
            try {
                resetDeviceConfig(context, /*isScoped=*/true, failedPackage);
            } catch (Exception e) {
                res = e;
            }
            break;
        case LEVEL_RESET_SETTINGS_TRUSTED_DEFAULTS:
            try {
                resetAllSettingsIfNecessary(context, Settings.RESET_MODE_TRUSTED_DEFAULTS,
                        level);
            } catch (Exception e) {
                res = e;
            }
            try {
                resetDeviceConfig(context, /*isScoped=*/false, failedPackage);
            } catch (Exception e) {
                res = e;
            }
            break;
        case LEVEL_WARM_REBOOT:
            // Request the reboot from a separate thread to avoid deadlock on PackageWatchdog
            // when device shutting down.
            SystemProperties.set(PROP_ATTEMPTING_REBOOT, "true");
            runnable = () -> {
                try {
                    PowerManager pm = context.getSystemService(PowerManager.class);
                    if (pm != null) {
                        pm.reboot(TAG);
                    }
                } catch (Throwable t) {
                    logRescueException(level, failedPackage, t);
                }
            };
            thread = new Thread(runnable);
            thread.start();
            break;
        case LEVEL_FACTORY_RESET:
            SystemProperties.set(PROP_ATTEMPTING_FACTORY_RESET, "true");
            runnable = new Runnable() {
                @Override
                public void run() {
                    try {
                        RecoverySystem.rebootPromptAndWipeUserData(context, TAG);
                    } catch (Throwable t) {
                        logRescueException(level, failedPackage, t);
                    }
                }
            };
            thread = new Thread(runnable);
            thread.start();
            break;
    }

    if (res != null) {
        throw res;
    }
}

触发场景：

（1）system_server 在 10 分钟内重启 5 次以上调整一次级别。（Android 12以前 为5分钟内5次）

（2）永久性系统应用在 50 秒内崩溃 5 次以上调整一次级别。（Android 12 以前 默认为30秒内5次）

当检测到上述某种情况时，救援程序会将其上报给下一救援级别、处理与该级别相关联的任务，并让设备继续运行，看看能否恢复。清除或重置内容的程度随级别而增加。最高级别会提示用户将设备恢复出厂设置。

别的逻辑都比较简单，我们看一下恢复出厂的逻辑：

//QSSI.13/frameworks/base/core/java/android/os/RecoverySystem.java
    public static void rebootPromptAndWipeUserData(Context context, String reason)
            throws IOException {
        boolean checkpointing = false;
        boolean needReboot = false;
        IVold vold = null;
        try {
            vold = IVold.Stub.asInterface(ServiceManager.checkService("vold"));
            if (vold != null) {
                checkpointing = vold.needsCheckpoint();
            } else  {
                Log.w(TAG, "Failed to get vold");
            }
        } catch (Exception e) {
            Log.w(TAG, "Failed to check for checkpointing");
        }

        // If we are running in checkpointing mode, we should not prompt a wipe.
        // Checkpointing may save us. If it doesn't, we will wind up here again.
        // 检测是否可以通过回滚消除问题，
        if (checkpointing) {
            try {
                vold.abortChanges("rescueparty", false);
                Log.i(TAG, "Rescue Party requested wipe. Aborting update");
            } catch (Exception