1.引言
最近在面试复习，对android知识重新梳理了一遍，争取做到以点到面，把知识点都串起来。PackageManagerService 是android 核心服务之一。授权/app安装都与之相关。本文主要讲下安装apk的流程和扫描apk的过程。
2.正题
2.1 packageService 服务启动，apk扫描过程
android中基本上每个cpp文件都对应一个名词一模一样的java文件，如surface.java 和surface.cpp ，Canves.java和Canves.cpp。包括本文的SystemServer.cpp和SystemServer.java。 往往c到java层的时候，都是调用java层的main方法。同理在系统初始化的时候，SystemServer.java的main方法会被调用.进而调用startBootstrapServices
/services/java/com/android/server/SystemServer.java
private void startBootstrapServices() {
....
traceBeginAndSlog("StartPackageManagerService");
try {
Watchdog.getInstance().pauseWatchingCurrentThread("packagemanagermain");
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
} finally {
Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");
}
....
}
/services/core/java/com/android/server/pm/PackageManagerService.java
public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
// Self-check for initial settings.
PackageManagerServiceCompilerMapping.checkProperties();
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
m.enableSystemUserPackages();
ServiceManager.addService("package", m);
final PackageManagerNative pmn = m.new PackageManagerNative();
ServiceManager.addService("package_native", pmn);
return m;
}
ServiceManager.addService("package", m);
将每个服务保存到Map中，需要的时候就根据名词获取IBinder的引用。扫描系统app的核心就是在PackageManagerService的构造方法中。
扫描特定目录下是否含有apk:
scanDirTracedLI(frameworkDir, systemParseFlags,
systemScanFlags | SCAN_NO_DEX | SCAN_AS_PRIVILEGED, 0);
if (!mPackages.containsKey("android")) {
throw new IllegalStateException(
"Failed to load frameworks package; check log for warnings");
}
for (int i = 0, size = mDirsToScanAsSystem.size(); i < size; i++) {
final SystemPartition partition = mDirsToScanAsSystem.get(i);
//扫描priv-app目录
if (partition.privAppFolder != null) {
scanDirTracedLI(partition.privAppFolder, systemParseFlags,
systemScanFlags | SCAN_AS_PRIVILEGED | partition.scanFlag, 0);
}
scanDirTracedLI(partition.appFolder, systemParseFlags,
systemScanFlags | partition.scanFlag, 0);
}
...
//扫描system/app目录下的内容
scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0);
scanDirTracedLI方法调用的事scanDirLI方法，此方法是用了俩个for循环，第一for循环不断解析apk生成ParseResult,并且向 ArrayBlockingQueue中保存，下一个for循环就是不停的取出。
for (File file : files) {
final boolean isPackage = (isApkFile(file) || file.isDirectory())
&& !PackageInstallerService.isStageName(file.getName());
if (!isPackage) {
// Ignore entries which are not packages
continue;
}
parallelPackageParser.submit(file, parseFlags);
fileCount++;
}
// Process results one by one
for (; fileCount > 0; fileCount--) {
ParallelPackageParser.ParseResult parseResult = parallelPackageParser.take();
Throwable throwable = parseResult.throwable;
int errorCode = PackageManager.INSTALL_SUCCEEDED;
}
// Delete invalid userdata apps
if ((scanFlags & SCAN_AS_SYSTEM) == 0 &&
errorCode != PackageManager.INSTALL_SUCCEEDED) {
logCriticalInfo(Log.WARN,
"Deleting invalid package at " + parseResult.scanFile);
removeCodePathLI(parseResult.scanFile);
}
}
}
services/core/java/com/android/server/pm/ParallelPackageParser.java
/**
* Submits the file for parsing
* @param scanFile file to scan
* @param parseFlags parse falgs
*/
public void submit(File scanFile, int parseFlags) {
mService.submit(() -> {
ParseResult pr = new ParseResult();
Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "parallel parsePackage [" + scanFile + "]");
try {
PackageParser pp = new PackageParser();
pp.setSeparateProcesses(mSeparateProcesses);
pp.setOnlyCoreApps(mOnlyCore);
pp.setDisplayMetrics(mMetrics);
pp.setCacheDir(mCacheDir);
pp.setCallback(mPackageParserCallback);
pr.scanFile = scanFile;
pr.pkg = parsePackage(pp, scanFile, parseFlags);
} catch (Throwable e) {
pr.throwable = e;
} finally {
Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
}
try {
mQueue.put(pr);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
// Propagate result to callers of take().
// This is helpful to prevent main thread from getting stuck waiting on
// ParallelPackageParser to finish in case of interruption
mInterruptedInThread = Thread.currentThread().getName();
}
});
}
解析的操作放在parsePackage()方法中,生成一个PackageParser.Package对象。
PackageParser类是真正执行解析apk的核心类，涉及到apk的解析操作。
经过层层调用，最终解析方法是PackageParser .parseBaseApkCommon。此方法会对Minifest.xml进行解析。得到四大组件，以及各个权限。以下是部分代码
String tagName = parser.getName();
if (tagName.equals("activity")) {
Activity a = parseActivity(owner, res, parser, flags, outError, cachedArgs, false,
owner.baseHardwareAccelerated);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.activities.add(a);
parsedComponent = a.info;
}
Package 类的结构:
public boolean baseHardwareAccelerated;
// For now we only support one application per package.
@UnsupportedAppUsage
public ApplicationInfo applicationInfo = new ApplicationInfo();
@UnsupportedAppUsage
public final ArrayList permissions = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList permissionGroups = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList activities = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList receivers = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList providers = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList services = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList instrumentation = new ArrayList(0);
@UnsupportedAppUsage
public final ArrayList requestedPermissions = new ArrayList();
/** Permissions requested but not in the manifest. */
public final ArrayList implicitPermissions = new ArrayList<>();
以上就是android 启动的时候 扫描app的过程。这个过程在安装apk的时候也会用到。
2.2 apk安装过程
分析安装过程先从应用层分析,入口在PackageInstallerActivity 这是系统默认的界面.点击ok之后，调用的事如下方法:
mAlert.setButton(DialogInterface.BUTTON_POSITIVE, getString(R.string.install),
(ignored, ignored2) -> {
if (mOk.isEnabled()) {
if (mSessionId != -1) {
mInstaller.setPermissionsResult(mSessionId, true);
finish();
} else {
startInstall();
}
}
}, null);
mAlert.setButton(DialogInterface.BUTTON_NEGATIVE, getString(R.string.cancel),
(ignored, ignored2) -> {
// Cancel and finish
setResult(RESULT_CANCELED);
if (mSessionId != -1) {
mInstaller.setPermissionsResult(mSessionId, false);
}
finish();
}, null);
setupAlert();
mInstaller.setPermissionsResult(mSessionId, true); 调用的PackageInstallerService的setPermissionsResult
@Override
public void setPermissionsResult(int sessionId, boolean accepted) {
// mContext.enforceCallingOrSelfPermission(android.Manifest.permission.INSTALL_PACKAGES, TAG);
synchronized (mSessions) {
PackageInstallerSession session = mSessions.get(sessionId);
if (session != null) {
session.setPermissionsResult(accepted);
}
}
}
mContext.enforceCallingOrSelfPermission 是分析的入口方法.
1.copy apk到data/app/
session.setPermissionsResult会发送一个MSG_COMMIT的Message.最终调用到了PackageManagerService.installStage方法。installStage方法发送了一个INIT_COPY的Message,将apk拷贝到data/app/
void doHandleMessage(Message msg) {
switch (msg.what) {
case INIT_COPY: {
HandlerParams params = (HandlerParams) msg.obj;
if (params != null) {
if (DEBUG_INSTALL) Slog.i(TAG, "init_copy: " + params);
Trace.asyncTraceEnd(TRACE_TAG_PACKAGE_MANAGER, "queueInstall",
System.identityHashCode(params));
Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "startCopy");
//开始copy,开始install
params.startCopy();
Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
}
break;
}
case SEND_PENDING_BROADCAST: {
2.processPendingInstall
processPendingInstall最终调用installPackagesLI方法。installPackagesLI是安装的核心。会继续调用prepareAppDataAfterInstallLIF方法
- 创建data/data用户数据：
- 将package信息写入到/data/system/package.xml
private void prepareAppDataAfterInstallLIF(PackageParser.Package pkg) {
final PackageSetting ps;
synchronized (mPackages) {
ps = mSettings.mPackages.get(pkg.packageName);
mSettings.writeKernelMappingLPr(ps);
}
final UserManagerService um = sUserManager;
UserManagerInternal umInternal = getUserManagerInternal();
for (UserInfo user : um.getUsers(false /* excludeDying */)) {
final int flags;
if (umInternal.isUserUnlockingOrUnlocked(user.id)) {
flags = StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE;
} else if (umInternal.isUserRunning(user.id)) {
flags = StorageManager.FLAG_STORAGE_DE;
} else {
continue;
}
if (ps.getInstalled(user.id)) {
// TODO: when user data is locked, mark that we're still dirty
prepareAppDataLIF(pkg, user.id, flags);
}
}
}