1. 简介

为了能把应用程序安装到SD卡和TF卡上，Android系统默认是不支持的，它只有一个asec mount点： /mnt/secure/asec，在我的系统中，此mount点由/mnt/sdcard给占用了，所以TF卡就支持不了。为了解决此问题，除了把代码读明白之外，无其它的办法。为了方便理解下面的描述，先看下Vold(管理外设热插拔)的系统框架图：

关于相关类图，引用其他仁兄的图：

2. 从U盘安装应用程序流程

PackageInstallerActivity.java::initiateInstall->
                             ::startInstallConfirm->
                   
InstallAppProgress::onCreate->
InstallAppProgress::initView->

PackageManager::installPackage->

PackageManagerService::installPackage->
 installPackageWithVerification->
       mHandler.sendMessage(msg)->

PackageHandler::handleMessage->
  PackageHandler::doHandleMessage->
  HandlerParams::startCopy->
     InstallParams::handleStartCopy-> (根据installLocation确认安装位置,只有针对/data分区有lowThreshold)
       SdInstallArgs::copyApk-> (关键的地方，下面详解)
     InstallParams::handleReturnCode->
       PackageManagerService::processPendingInstall->
         PackageManagerService::installPackageLI-> //args, res分析
           PackageManagerService::installNewPackageLI->  // or replacePackageLI
             PackageManagerService::scanPackageLI-> (KEY)->parsePackage(解析AndroidManifest.xml)
               Installer::install (mInstaller.install)-> (Socket)--->
               installd(真正做事的地方)

2.1 SdInstallArgs::copyApk

SdInstallArgs::copyApk->
DefaultContainerService::copyResourceInner->
PackageHelper::createSdDir->
MountService::createSecureContainer->

(cmd = String.format(new Locale("en", "Us"),

"asec create %s %d %s %s %d", id, sizeMb, fstype, key, ownerUid);)
NativeDaemonConnector::doCommandLocked->(向"vold" socket发送命令给vold，并等待结果)
NativeDaemonConnector::sendCommandLocked-> (Socket)

FrameworkListener::onDataAvailable-> (receive message)  "buffer=asec list"
                                  或"buffer=asec create smdl2tmp1 19 fat caf791d0426d682e5b2aafc5439d55a9 10023"
FrameworkListener::dispatchCommand->
CommandListener::AsecCmd::runCommand-> (所有与Volume::SEC_ASECDIR相关的代码都需要修改)
VolumeManager::createAsec (决定安装文件的路径Volume::SEC_ASECDIR)

2.2 复杂的mount关系

详细代码参见Volume.cpp::

代码默认不把sdcard && udisk mount为asec，为此需要把SD卡或TF卡mount到asec挂载点，当然系统默认只有一个/mnt/secure/asec,你可以在init.rc中创建一个/mnt/secure/asecsd或/mnt/secure/asectf，并执行mount即可。

• /mnt/secure: 下的mount点为物理外设的mount点

•/mnt/asec: 为公共挂载点，它是一个tmpfs文件系统的挂载点，安装到SD或TF上的应用程序都可以被mount到此目录下的mount点

复杂的mount关系如下所示：

1) /dev/block/vold/31:9    mount to /mnt/secure/staging
   2) /mnt/secure/staging/.android_secure mount to /mnt/secure/asec (MS_BIND)
   3) tmpfs  mount to /mnt/secure/staging/.android_secure (只读0字节tmpfs,把它隐藏起来, obscuring the asec image directory from non root users)
   4) 把/mnt/secure/staging下的子目录(.android_secure)移动到/mnt/sdcard下

   注：MS_BIND: 执行bind挂载，使文件或者子目录树在文件系统内的另一个点上可视。

搞这么复杂的目的只有一个：只有root用户才能查看/mnt/secure/asec下的文件，当然把TF卡取出来，在Widows上可以看到.android_secure目录下的.asec文件。

2.3 把APK安装到SD卡或TF卡上留下的东东

当把APK安装到SD卡或TF卡上时，将在以下地方留下它的东东：

1) /mnt/secure/asec: (安装之后产生的.asec文件，它才是真正的内容)
   -rwxrwxr-x system   sdcard_rw 20257280 2013-04-07 06:14 com.myarrow.test-1.asec

2) /mnt/asec/com.myarrow.test-1: (是被mount上去的，它是一个tmpfs，并不真正占用flash空间)
   dr-xr-xr-x system   root              2013-04-07 06:14 lib
   -r-xr-xr-x system   root      4973096 2013-04-07 06:14 pkg.apk

3) /data/data/com.myarrow.test: (只是一个链接，不真正占用flash空间)
   lrwxrwxrwx system   system            2013-04-09 06:51 lib -> /mnt/asec/com.myarrow.test-1/lib

4) /data/dalvik-cache: (包含apk包中的dex文件，它占用data分区的flash空间, 所以data分区必须预留空间)
   -rw-r--r-- system   app_58      36608 2013-04-07 06:14 mnt@asec@com.myarrow.test-1@pkg.apk@classes.dex

3. 需要修改的主要文件

1) Volume.cpp

修改其中的mountVol/unmountVol，把SD或TF卡也执行bindmount

2) DefaultContainerService.java

修改isUnderExternalThreshold，当空间不足时，看看SD或TF卡上是否有足够的空间

3) VolumeManager.cpp

扩展与Volume::SEC_ASECDIR相关的地方，因为我们增加了一个Volume::SEC_SD_ASECDIR

4. Mount和Unmoun asec t流程

1) Mount:

MountService.java (notifyVolumeStateChange/onEvent)->
MountService.jvav (updatePublicVolumeState) ->
PackageManagerService.java (updateExternalMediaStatus) ->
                          (updateExternalMediaStatusInner) ->
                           (loadMediaPackages) ->
                           SdInstallArgs.doPreInstall->
PackageHelper.java (mountSdDir) ->
MountService.java(mountSecureContainer)->
CommandListener.cpp(CommandListener::AsecCmd::runCommand)

2) Unmount:
MountService.java (notifyVolumeStateChange/onEvent)->
MountService.jvav (updatePublicVolumeState) ->
PackageManagerService.java (updateExternalMediaStatus) ->
                          (updateExternalMediaStatusInner) ->
                           (unloadMediaPackages) ->(send UPDATED_MEDIA_STATUS)
                           PackageHandler.doHandleMessage (get UPDATED_MEDIA_STATUS)->
                           unloadAllContainers ->
                           (SdInstallArgs.doPostDeleteLI)->

PackageHelper.java (unMountSdDir) ->
MountService.java (unmountSecureContainer)->
CommandListener.cpp(CommandListener::AsecCmd::runCommand)

5.  copyResourceInner

其详细代码如下所示：

    private String copyResourceInner(Uri packageURI, String newCid, String key, String resFileName) {        // Make sure the sdcard is mounted.        String status = Environment.getExternalStorageState();        if (!status.equals(Environment.MEDIA_MOUNTED)) {            Slog.w(TAG, "Make sure sdcard is mounted.");            return null;        }        // The .apk file        String codePath = packageURI.getPath();        File codeFile = new File(codePath);        // Calculate size of container needed to hold base APK.        int sizeMb;        try {            sizeMb = calculateContainerSize(codeFile);        } catch (FileNotFoundException e) {            Slog.w(TAG, "File does not exist when trying to copy " + codeFile.getPath());            return null;        }        // Create new container        final String newCachePath;        if ((newCachePath = PackageHelper.createSdDir(sizeMb, newCid, key, Process.myUid())) == null) {            Slog.e(TAG, "Failed to create container " + newCid);            return null;        }        /*if (localLOGV)*/ {            Slog.i(TAG, "Created container for " + newCid + " at path : " + newCachePath);        }        final File resFile = new File(newCachePath, resFileName);        if (FileUtils.copyFile(new File(codePath), resFile)) {            /*if (localLOGV)*/ {                Slog.i(TAG, "Copied " + codePath + " to " + resFile);            }        } else {            Slog.e(TAG, "Failed to copy " + codePath + " to " + resFile);            // Clean up container            PackageHelper.destroySdDir(newCid);            return null;        }        final File sharedLibraryDir = new File(newCachePath, LIB_DIR_NAME);        if (sharedLibraryDir.mkdir()) {            int ret = NativeLibraryHelper.copyNativeBinariesIfNeededLI(codeFile, sharedLibraryDir);            if (ret != PackageManager.INSTALL_SUCCEEDED) {                Slog.e(TAG, "Could not copy native libraries to " + sharedLibraryDir.getPath());                PackageHelper.destroySdDir(newCid);                return null;            }        } else {            Slog.e(TAG, "Could not create native lib directory: " + sharedLibraryDir.getPath());            PackageHelper.destroySdDir(newCid);            return null;        }        if (!PackageHelper.finalizeSdDir(newCid)) {            Slog.e(TAG, "Failed to finalize " + newCid + " at path " + newCachePath);            // Clean up container            PackageHelper.destroySdDir(newCid);            return null;        }        if (localLOGV) {            Slog.i(TAG, "Finalized container " + newCid);        }        if (PackageHelper.isContainerMounted(newCid)) {            if (localLOGV) {                Slog.i(TAG, "Unmounting " + newCid + " at path " + newCachePath);            }            // Force a gc to avoid being killed.            Runtime.getRuntime().gc();            PackageHelper.unMountSdDir(newCid);        } else {            if (localLOGV) {                Slog.i(TAG, "Container " + newCid + " not mounted");            }        }        return newCachePath;    }

其主要功能为：

1）创建.asec文件

2）copy apk

3）copy lib

4）final .asec文件

其详细log信息如下：

D/VoldVolumeManager(   85):  createAsec(367) call createImageFile   E/Vold    (   85): createImageFile(236) call creat                  E/Vold    (   85): createImageFile(241) call ftruncate              E/Vold    (   85): createImageFile(247) END                         D/VoldVolumeManager(   85): createAsec(374) call asecHash           D/VoldVolumeManager(   85): createAsec(383) call Loop::create       D/VoldVolumeManager(   85): createAsec(397) call Devmapper::create  D/VoldVolumeManager(   85): createAsec(414) call open               D/VoldVolumeManager(   85): createAsec(436) write sb                D/VoldVolumeManager(   85): createAsec(453) Fat::format             D/VoldVolumeManager(   85): createAsec(477) Fat::doMount            D/VoldVolumeManager(   85): createAsec(491) End                                                                                         ****copy apk and lib*****                                                                                                               D/VoldVolumeManager(   85): finalizeAsec(502) start                 D/VoldVolumeManager(   85): finalizeAsec(520) End                   D/VoldVolumeManager(   85): renameAsec:538 Volume::SEC_ASECDIR startD/VoldVolumeManager(   85): renameAsec:538 Volume::SEC_ASECDIR start