recovery 根据@/cache/recovery/block.map描述从data分区升级

随着android版本的更新，系统固件的大小也越来越大，升级包也越来越大，cache分区已经不够存储update.zip了，所以应用把update.zip下载到data分区，默认情况下data分区是可以存储升级包的。

我们有分区加密的功能，当打开加密分区后，data分区是加密的，当升级包存在data分区的时候，recovery下获取不到对应的秘钥，也没有对应的程序去解密，所以recovery无法正常挂载data分区，获取升级包升级。那么google是如何完成分区加密时，从data分区升级的呢？

当应用从远程服务器下载update.zip升级包后，是如何一步步进入recovery升级的呢？

android P（9.0）aosp code：

frameworks/base/core/java/android/os/RecoverySystem.java

主要分为两步进行，第一步处理升级包（processPackage），第二步安装升级包（installPackage）：

处理升级包：

public static void processPackage(Context context, File packageFile, final ProgressListener listener, final Handler handler) throws IOException { String filename = packageFile.getCanonicalPath(); if (!filename.startsWith("/data/")) { return; } RecoverySystem rs = (RecoverySystem) context.getSystemService(Context.RECOVERY_SERVICE); IRecoverySystemProgressListener progressListener = null; if (listener != null) { final Handler progressHandler; if (handler != null) { progressHandler = handler; } else { progressHandler = new Handler(context.getMainLooper()); } progressListener = new IRecoverySystemProgressListener.Stub() { int lastProgress = 0; long lastPublishTime = System.currentTimeMillis(); @Override public void onProgress(final int progress) { final long now = System.currentTimeMillis(); progressHandler.post(new Runnable() { @Override public void run() { if (progress > lastProgress && now - lastPublishTime > PUBLISH_PROGRESS_INTERVAL_MS) { lastProgress = progress; lastPublishTime = now; listener.onProgress(progress); } } }); } }; } if (!rs.uncrypt(filename, progressListener)) { throw new IOException("process package failed"); } }

主要做了如下工作：

（1）只处理升级包在/data分区的场景

（2）处理进度显示

（3）调用rs.uncrypt(filename, progressListener) 处理升级包

    /**
     * Talks to RecoverySystemService via Binder to trigger uncrypt.
     */
    private boolean uncrypt(String packageFile, IRecoverySystemProgressListener listener) { try { return mService.uncrypt(packageFile, listener); } catch (RemoteException unused) { } return false; }

RecoverySystem 通过Binder 触发 uncrypt服务

/system/etc/init/uncrypt.rc

service uncrypt /system/bin/uncrypt
    class main
    socket uncrypt stream 600 system system disabled oneshot service setup-bcb /system/bin/uncrypt --setup-bcb class main socket uncrypt stream 600 system system disabled oneshot service clear-bcb /system/bin/uncrypt --clear-bcb class main socket uncrypt stream 600 system system disabled oneshot

调用了/system/bin/uncrypt程序来处理升级包， uncrypt对应的源码在 bootable/recovery/uncrypt/uncrypt.cpp

具体处理细节我们在章节详解：recovery uncrypt功能解析(bootable/recovery/uncrypt/uncrypt.cpp)

安装升级包：

 public static void installPackage(Context context, File packageFile, boolean processed) throws IOException { synchronized (sRequestLock) { LOG_FILE.delete(); // Must delete the file in case it was created by system server. UNCRYPT_PACKAGE_FILE.delete(); String filename = packageFile.getCanonicalPath(); Log.w(TAG, "!!! REBOOTING TO INSTALL " + filename + " !!!"); // If the package name ends with "_s.zip", it's a security update. boolean securityUpdate = filename.endsWith("_s.zip"); // If the package is on the /data partition, the package needs to // be processed (i.e. uncrypt'd). The caller specifies if that has // been done in 'processed' parameter. if (filename.startsWith("/data/")) { if (processed) { if (!BLOCK_MAP_FILE.exists()) { Log.e(TAG, "Package claimed to have been processed but failed to find " + "the block map file."); throw new IOException("Failed to find block map file"); } } else { FileWriter uncryptFile = new FileWriter(UNCRYPT_PACKAGE_FILE); try { uncryptFile.write(filename + "\n"); } finally { uncryptFile.close(); } // UNCRYPT_PACKAGE_FILE needs to be readable and writable // by system server. if (!UNCRYPT_PACKAGE_FILE.setReadable(true, false) || !UNCRYPT_PACKAGE_FILE.setWritable(true, false)) { Log.e(TAG, "Error setting permission for " + UNCRYPT_PACKAGE_FILE); } BLOCK_MAP_FILE.delete(); } // If the package is on the /data partition, use the block map // file as the package name instead. filename = "@/cache/recovery/block.map"; } final String filenameArg = "--update_package=" + filename + "\n"; final String localeArg = "--locale=" + Locale.getDefault().toLanguageTag() + "\n"; final String securityArg = "--security\n"; String command = filenameArg + localeArg; if (securityUpdate) { command += securityArg; } RecoverySystem rs = (RecoverySystem) context.getSystemService( Context.RECOVERY_SERVICE); if (!rs.setupBcb(command)) { throw new IOException("Setup BCB failed"); } // Having set up the BCB (bootloader control block), go ahead and reboot PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE); String reason = PowerManager.REBOOT_RECOVERY_UPDATE; // On TV, reboot quiescently if the screen is off if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_LEANBACK)) { WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); if (wm.getDefaultDisplay().getState() != Display.STATE_ON) { reason += ",quiescent"; } } pm.reboot(reason); throw new IOException("Reboot failed (no permissions?)"); } }

主要做了如下工作：

（1）如果升级包路径为/data开始的根目录，把升级包的名字写到文件/cache/recovery/uncrypt_file里

（2）写升级命令--update_package=@/cache/recovery/block.map到文件/cache/recovery/command

（3）调用pm.reboot(PowerManager.REBOOT_RECOVERY_UPDATE)重启。

参考资料：https://blog.csdn.net/miaotao/article/details/45129423

http://feed.askmaclean.com/archives/linux查看稀疏文件的哪些块没有分配空间.html

recovery 根据@/cache/recovery/block.map描述从data分区升级

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