Android 上层RecoverySystem类

尝试将imx51使用OTA方式进行recovery，将android_recovery.img放入/cache/分区下然后再下一次重启的时候进行分区更新,但发现放入的文件会被莫名删除，logcat中搜索到recovery相关log，tag为recoverysystem，尝试在android工程framework的os代码中寻找代码，找到相关代码，代码最后有将cache分区进行删除仅保留last_log的操作，这才解开心中的疑惑，而且发现，以前本地升级时写文件的代码其实不需要自己写的，android自己已经做好了类的函数，需要的只是调用。代码很简单，和recovery的代码几乎一样，java话而已，无须一条条解释代码。List as below:

部分中文解释为下：（参考http://www.elexcon.com/news/54208.html）

从Android 2.2开始新增RecoverySystem类，可以帮助我们调用系统还原等操作，使用RecoverySystem必须是API Level最小为为8，该类位于android.os.RecoverySystem，提供了三个静态方法

  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 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。

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

 /*
  * Copyright (C) 2010 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.os;

 import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
 import android.util.Log;

 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.security.GeneralSecurityException;
 import java.security.PublicKey;
 import java.security.Signature;
 import java.security.SignatureException;
 import java.security.cert.Certificate;
 import java.security.cert.CertificateFactory;
 import java.security.cert.X509Certificate;
 import java.util.Collection;
 import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;

 import org.apache.harmony.security.asn1.BerInputStream;
 import org.apache.harmony.security.pkcs7.ContentInfo;
 import org.apache.harmony.security.pkcs7.SignedData;
 import org.apache.harmony.security.pkcs7.SignerInfo;
 import org.apache.harmony.security.provider.cert.X509CertImpl;

 /**
  * RecoverySystem contains methods for interacting with the Android
  * recovery system (the separate partition that can be used to install
  * system updates, wipe user data, etc.)
  */
 public class RecoverySystem {
     private static final String TAG = "RecoverySystem";

     /**
      * Default location of zip file containing public keys (X509
      * certs) authorized to sign OTA updates.
      */
     private static final File DEFAULT_KEYSTORE =
         new File("/system/etc/security/otacerts.zip");

     /** Send progress to listeners no more often than this (in ms). */
     private static final long PUBLISH_PROGRESS_INTERVAL_MS = 500;

     /** Used to communicate with recovery.  See bootable/recovery/recovery.c. */
     private static File RECOVERY_DIR = new File("/cache/recovery");
     private static File COMMAND_FILE = new File(RECOVERY_DIR, "command");
     private static File LOG_FILE = new File(RECOVERY_DIR, "log");
     private static String LAST_LOG_FILENAME = "last_log";

     // Length limits for reading files.
     private static int LOG_FILE_MAX_LENGTH = 64 * 1024;

     /**
      * Interface definition for a callback to be invoked regularly as
      * verification proceeds.
      */
     public interface ProgressListener {
         /**
          * Called periodically as the verification progresses.
          *
          * @param progress  the approximate percentage of the
          *        verification that has been completed, ranging from 0
          *        to 100 (inclusive).
          */
         public void onProgress(int progress);
     }

     /** @return the set of certs that can be used to sign an OTA package. */
     private static HashSet getTrustedCerts(File keystore)
         throws IOException, GeneralSecurityException {
         HashSet trusted = new HashSet();
         if (keystore == null) {
             keystore = DEFAULT_KEYSTORE;
         }
         ZipFile zip = new ZipFile(keystore);
         try {
             CertificateFactory cf = CertificateFactory.getInstance("X.509");
             Enumerationextends ZipEntry> entries = zip.entries();
             while (entries.hasMoreElements()) {
                 ZipEntry entry = entries.nextElement();
                 trusted.add(cf.generateCertificate(zip.getInputStream(entry)));
             }
         } finally {
             zip.close();
         }
         return trusted;
     }

     /**
      * Verify the cryptographic signature of a system update package
      * before installing it.  Note that the package is also verified
      * separately by the installer once the device is rebooted into
      * the recovery system.  This function will return only if the
      * package was successfully verified; otherwise it will throw an
      * exception.
      *
      * Verification of a package can take significant time, so this
      * function should not be called from a UI thread.  Interrupting
      * the thread while this function is in progress will result in a
      * SecurityException being thrown (and the thread's interrupt flag
      * will be cleared).
      *
      * @param packageFile  the package to be verified
      * @param listener     an object to receive periodic progress
      * updates as verification proceeds.  May be null.
      * @param deviceCertsZipFile  the zip file of certificates whose
      * public keys we will accept.  Verification succeeds if the
      * package is signed by the private key corresponding to any
      * public key in this file.  May be null to use the system default
      * file (currently "/system/etc/security/otacerts.zip").
      *
      * @throws IOException if there were any errors reading the
      * package or certs files.
      * @throws GeneralSecurityException if verification failed
      */
     public static void verifyPackage(File packageFile,
                                      ProgressListener listener,
                                      File deviceCertsZipFile)
         throws IOException, GeneralSecurityException {
         long fileLen = packageFile.length();

         RandomAccessFile raf = new RandomAccessFile(packageFile, "r");
         try {
             int lastPercent = 0;
             long lastPublishTime = System.currentTimeMillis();
             if (listener != null) {
                 listener.onProgress(lastPercent);
             }

             raf.seek(fileLen - 6);
             byte[] footer = new byte[6];
             raf.readFully(footer);

             if (footer[2] != (byte)0xff || footer[3] != (byte)0xff) {
                 throw new SignatureException("no signature in file (no footer)");
             }

             int commentSize = (footer[4] & 0xff) | ((footer[5] & 0xff) << 8);
             int signatureStart = (footer[0] & 0xff) | ((footer[1] & 0xff) << 8);
             Log.v(TAG, String.format("comment size %d; signature start %d",
                                      commentSize, signatureStart));

             byte[] eocd = new byte[commentSize + 22];
             raf.seek(fileLen - (commentSize + 22));
             raf.readFully(eocd);

             // Check that we have found the start of the
             // end-of-central-directory record.
             if (eocd[0] != (byte)0x50 || eocd[1] != (byte)0x4b ||
                 eocd[2] != (byte)0x05 || eocd[3] != (byte)0x06) {
                 throw new SignatureException("no signature in file (bad footer)");
             }

             for (int i = 4; i < eocd.length-3; ++i) {
                 if (eocd[i  ] == (byte)0x50 && eocd[i+1] == (byte)0x4b &&
                     eocd[i+2] == (byte)0x05 && eocd[i+3] == (byte)0x06) {
                     throw new SignatureException("EOCD marker found after start of EOCD");
                 }
             }

             // The following code is largely copied from
             // JarUtils.verifySignature().  We could just *call* that
             // method here if that function didn't read the entire
             // input (ie, the whole OTA package) into memory just to
             // compute its message digest.

             BerInputStream bis = new BerInputStream(
                 new ByteArrayInputStream(eocd, commentSize+22-signatureStart, signatureStart));
             ContentInfo info = (ContentInfo)ContentInfo.ASN1.decode(bis);
             SignedData signedData = info.getSignedData();
             if (signedData == null) {
                 throw new IOException("signedData is null");
             }
             Collection encCerts = signedData.getCertificates();
             if (encCerts.isEmpty()) {
                 throw new IOException("encCerts is empty");
             }
             // Take the first certificate from the signature (packages
             // should contain only one).
             Iterator it = encCerts.iterator();
             X509Certificate cert = null;
             if (it.hasNext()) {
                 cert = new X509CertImpl((org.apache.harmony.security.x509.Certificate)it.next());
             } else {
                 throw new SignatureException("signature contains no certificates");
             }

             List sigInfos = signedData.getSignerInfos();
             SignerInfo sigInfo;
             if (!sigInfos.isEmpty()) {
                 sigInfo = (SignerInfo)sigInfos.get(0);
             } else {
                 throw new IOException("no signer infos!");
             }

             // Check that the public key of the certificate contained
             // in the package equals one of our trusted public keys.

             HashSet trusted = getTrustedCerts(
                 deviceCertsZipFile == null ? DEFAULT_KEYSTORE : deviceCertsZipFile);

             PublicKey signatureKey = cert.getPublicKey();
             boolean verified = false;
             for (Certificate c : trusted) {
                 if (c.getPublicKey().equals(signatureKey)) {
                     verified = true;
                     break;
                 }
             }
             if (!verified) {
                 throw new SignatureException("signature doesn't match any trusted key");
             }

             // The signature cert matches a trusted key.  Now verify that
             // the digest in the cert matches the actual file data.

             // The verifier in recovery *only* handles SHA1withRSA
             // signatures.  SignApk.java always uses SHA1withRSA, no
             // matter what the cert says to use.  Ignore
             // cert.getSigAlgName(), and instead use whatever
             // algorithm is used by the signature (which should be
             // SHA1withRSA).

             String da = sigInfo.getdigestAlgorithm();
             String dea = sigInfo.getDigestEncryptionAlgorithm();
             String alg = null;
             if (da == null || dea == null) {
                 // fall back to the cert algorithm if the sig one
                 // doesn't look right.
                 alg = cert.getSigAlgName();
             } else {
                 alg = da + "with" + dea;
             }
             Signature sig = Signature.getInstance(alg);
             sig.initVerify(cert);

             // The signature covers all of the OTA package except the
             // archive comment and its 2-byte length.
             long toRead = fileLen - commentSize - 2;
             long soFar = 0;
             raf.seek(0);
             byte[] buffer = new byte[4096];
             boolean interrupted = false;
             while (soFar < toRead) {
                 interrupted = Thread.interrupted();
                 if (interrupted) break;
                 int size = buffer.length;
                 if (soFar + size > toRead) {
                     size = (int)(toRead - soFar);
                 }
                 int read = raf.read(buffer, 0, size);
                 sig.update(buffer, 0, read);
                 soFar += read;

                 if (listener != null) {
                     long now = System.currentTimeMillis();
                     int p = (int)(soFar * 100 / toRead);
                     if (p > lastPercent &&
                         now - lastPublishTime > PUBLISH_PROGRESS_INTERVAL_MS) {
                         lastPercent = p;
                         lastPublishTime = now;
                         listener.onProgress(lastPercent);
                     }
                 }
             }
             if (listener != null) {
                 listener.onProgress(100);
             }

             if (interrupted) {
                 throw new SignatureException("verification was interrupted");
             }

             if (!sig.verify(sigInfo.getEncryptedDigest())) {
                 throw new SignatureException("signature digest verification failed");
             }
         } finally {
             raf.close();
         }
     }

     /**
      * 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);
     }

     /**
      * 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 /data partition and toggle
      * Encrypted File Systems on/off.
      * @param extras to add to the RECOVERY_COMPLETED intent after rebooting.
      * @throws IOException if something goes wrong.
      *
      * @hide
      */
     public static void rebootToggleEFS(Context context, boolean efsEnabled)
         throws IOException {
         if (efsEnabled) {
             bootCommand(context, "--set_encrypted_filesystem=on");
         } else {
             bootCommand(context, "--set_encrypted_filesystem=off");
         }
     }

     /**
      * 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);
         try {
             command.write(arg);
             command.write("\n");
         } finally {
             command.close();
         }

         // Having written the command file, go ahead and reboot
         PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
         pm.reboot("recovery");

         throw new IOException("Reboot failed (no permissions?)");
     }

     /**
      * Called after booting to process and remove recovery-related files.
      * @return the log file from recovery, or null if none was found.
      *
      * @hide
      */
     public static String handleAftermath() {
         // Record the tail of the LOG_FILE
         String log = null;
         try {
             log = FileUtils.readTextFile(LOG_FILE, -LOG_FILE_MAX_LENGTH, "...\n");
         } catch (FileNotFoundException e) {
             Log.i(TAG, "No recovery log file");
         } catch (IOException e) {
             Log.e(TAG, "Error reading recovery log", e);
         }

         // Delete everything in RECOVERY_DIR except LAST_LOG_FILENAME
         String[] names = RECOVERY_DIR.list();
         for (int i = 0; names != null && i < names.length; i++) {
             if (names[i].equals(LAST_LOG_FILENAME)) continue;
             File f = new File(RECOVERY_DIR, names[i]);
             if (!f.delete()) {
                 Log.e(TAG, "Can't delete: " + f);
             } else {
                 Log.i(TAG, "Deleted: " + f);
             }
         }

         return log;
     }

     private void RecoverySystem() { }  // Do not instantiate
 }