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 start
D/VoldVolumeManager( 85): renameAsec:538 Volume::SEC_ASECDIR start