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

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