recovery升级流程分析

在系统升级这方面，recovery升级方式起着非常重要的作用，所谓recovery升级指的是在进行升级的时候，启动到recovery模式(类似于正常模式)，开始对指定的分区进行升级，升级完成后启动到正常模式。

从应用层开始分析recovery的流程。

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

    @SystemApi
    @RequiresPermission(android.Manifest.permission.RECOVERY)
    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?)");
        }
    }

　在该方法中传入的参数为上下文，升级包文件和是否被uncrypt'd处理过。