安卓应用安装过程学习

声明：此文章来自http://shuwoom.com/?p=60的学习记录

启动式安装

public static final IPackageManager main(Context context, Installer installer,
    boolean factoryTest, boolean onlyCore) {
        PackageManagerService m = new PackageManagerService(context, installer, factoryTest, onlyCore);
        ServiceManager.addService("package", m);
        return m;
}

main函数中创建PackageManagerService服务对象，并把服务添加到ServiceManager中

ServiceManager是Android系统Binder进程通信机制的守护进程，一直运行在后台。它主要负责管理系统中的Binder对象。

应用程序在安装时涉及到如下几个重要目录：

system/app	系统应用程序的目录
data/app	用户程序安装的目录
data/data	存放应用程序数据的目录
data/dalvik-cache	存放的是经过优化的dex文件

PackageManagerService是Android系统的核心服务之一，在系统启动的时候由SystemServer组件负责启动起来。PackageManagerService用于管理系统中的所有安装包信息以及应用程序的安装和卸载，但是实际应用程序的安装卸载并不是由PackageManagerService亲自完成，而是通过socket通信，PackageManagerService来访问installd服务来实现应用程序的安装和卸载。

public class SystemServer {
    ...
    /**
     * Called to initialize native system services.
    */
    private static native void nativeInit();
    public static void main(String[] args) {
    ...
    System.loadLibrary("android_servers");

    Slog.i(TAG, "Entered the Android system server!");

    // Initialize native services.
    nativeInit();
    // This used to be its own separate thread, but now it is
    // just the loop we run on the main thread.
    ServerThread thr = new ServerThread();
    thr.initAndLoop();
    }
}

SystemServer中的ServerThread来启动PackageManagerService

class ServerThread {
    private static final String TAG = "SystemServer";
    ……
    ContentResolver mContentResolver;
    ……

    public void initAndLoop() {
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN,
        SystemClock.uptimeMillis());
        Looper.prepareMainLooper();

        ……
        boolean onlyCore = false;
        boolean firstBoot = false;
        ……
        try {
            Slog.i(TAG, "Display Manager");
            display = new DisplayManagerService(context, wmHandler);
            ServiceManager.addService(Context.DISPLAY_SERVICE, display, true);

            Slog.i(TAG, "Telephony Registry");
            telephonyRegistry = new TelephonyRegistry(context);
            ServiceManager.addService("telephony.registry", telephonyRegistry);

            Slog.i(TAG, "Scheduling Policy");
            ServiceManager.addService("scheduling_policy", new SchedulingPolicyService());

            AttributeCache.init(context);

            if (!display.waitForDefaultDisplay()) {
                reportWtf("Timeout waiting for default display to be initialized.",
                        new Throwable());
            }

            Slog.i(TAG, "Package Manager");
            // 处于加密状态时，紧解析核心应用
            String cryptState = SystemProperties.get("vold.decrypt");
            if (ENCRYPTING_STATE.equals(cryptState)) {
                Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
                onlyCore = true;
            } else if (ENCRYPTED_STATE.equals(cryptState)) {
                Slog.w(TAG, "Device encrypted - only parsing core apps");
                onlyCore = true;
            }

            pm = PackageManagerService.main(context, installer,
                    factoryTest != SystemServer.FACTORY_TEST_OFF,
                    onlyCore);
            
           ……
      }
}

PackageManagerService构造函数如下

public PackageManagerService(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
    synchronized (mInstallLock) {
        // writer
        synchronized (mPackages) {
            mHandlerThread.start();
            mHandler = new PackageHandler(mHandlerThread.getLooper());
            Watchdog.getInstance().addThread(mHandler, mHandlerThread.getName(),
                    WATCHDOG_TIMEOUT);

            File dataDir = Environment.getDataDirectory();
            mAppDataDir = new File(dataDir, "data");  
            mAppInstallDir = new File(dataDir, "app");  
            mAppLibInstallDir = new File(dataDir, "app-lib"); 
            mAsecInternalPath = new File(dataDir, "app-asec").getPath();  
            mUserAppDataDir = new File(dataDir, "user");  
            mDrmAppPrivateInstallDir = new File(dataDir, "app-private"); 
            ……
            mFrameworkDir = new File(Environment.getRootDirectory(), "framework");
            mDalvikCacheDir = new File(dataDir, "dalvik-cache");
            ……
           // Find base frameworks (resource packages without code).
            mFrameworkInstallObserver = new AppDirObserver(
                frameworkDir.getPath(), OBSERVER_EVENTS, true, false);
            mFrameworkInstallObserver.startWatching();
            //扫描”/system/framework”目录下的apk
            scanDirLI(frameworkDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR
                    | PackageParser.PARSE_IS_PRIVILEGED,
                    scanMode | SCAN_NO_DEX, 0);

            // Collected privileged system packages.
            File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
            mPrivilegedInstallObserver = new AppDirObserver(
                    privilegedAppDir.getPath(), OBSERVER_EVENTS, true, true);
            mPrivilegedInstallObserver.startWatching();
            //扫描”/system/priv-app”目录下的apk
            scanDirLI(privilegedAppDir, PackageParser.PARSE_IS_SYSTEM
                        | PackageParser.PARSE_IS_SYSTEM_DIR
                        | PackageParser.PARSE_IS_PRIVILEGED, scanMode, 0);

            // Collect ordinary system packages.
            File systemAppDir = new File(Environment.getRootDirectory(), "app"); 
            mSystemInstallObserver = new AppDirObserver(
                systemAppDir.getPath(), OBSERVER_EVENTS, true, false);
            mSystemInstallObserver.startWatching();
            //扫描”/system/app”目录下的apk
            scanDirLI(systemAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);

            // Collect all vendor packages.
            File vendorAppDir = new File("/vendor/app");
            mVendorInstallObserver = new AppDirObserver(
                vendorAppDir.getPath(), OBSERVER_EVENTS, true, false);
            mVendorInstallObserver.startWatching();
            // vender目录其实连接到/system/vendor，实际扫描:/system/vendor/app目录下的apk
            scanDirLI(vendorAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);

            if (DEBUG_UPGRADE) Log.v(TAG, "Running installd update commands");
            mInstaller.moveFiles();

            // Prune any system packages that no longer exist.
            final List<String> possiblyDeletedUpdatedSystemApps = new ArrayList<String>();
           //由上一部分内容知道，默认情况下磁盘加密状态关闭，即mOnlyCore状态false
           if (!mOnlyCore) {
                EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,
                        SystemClock.uptimeMillis());
                mAppInstallObserver = new AppDirObserver(
                    mAppInstallDir.getPath(), OBSERVER_EVENTS, false, false);
                mAppInstallObserver.startWatching();
                //扫描”/data/app”目录下的apk
                scanDirLI(mAppInstallDir, 0, scanMode, 0);
    
                mDrmAppInstallObserver = new AppDirObserver(
                    mDrmAppPrivateInstallDir.getPath(), OBSERVER_EVENTS, false, false);
                mDrmAppInstallObserver.startWatching();
                //扫描”/data/app-private”目录下的apk
                scanDirLI(mDrmAppPrivateInstallDir, PackageParser.PARSE_FORWARD_LOCK,
                        scanMode, 0);

                ……
            } 
        ……..
}

这里调用了很多scanDirLI，这个函数调用了scanPackageLI

private void scanDirLI(File dir, int flags, int scanMode, long currentTime) {
    String[] files = dir.list();
    ……

    int i;
    for (i=0; i<files.length; i++) {
        File file = new File(dir, files[i]);
        //只扫描apk后缀的文件
        if (!isPackageFilename(files[i])) {
            // Ignore entries which are not apk's
            continue;
        }
        
        PackageParser.Package pkg = scanPackageLI(file,
                flags|PackageParser.PARSE_MUST_BE_APK, scanMode, currentTime, null);
       ……
    }
}

scanPackageLI功能如下

private PackageParser.Package scanPackageLI(File scanFile,
    int parseFlags, int scanMode, long currentTime, UserHandle user) {
    ……
    String scanPath = scanFile.getPath();
    parseFlags |= mDefParseFlags;
    PackageParser pp = new PackageParser(scanPath);
    pp.setSeparateProcesses(mSeparateProcesses);
    pp.setOnlyCoreApps(mOnlyCore);
    //解析安装包
    final PackageParser.Package pkg = pp.parsePackage(scanFile, scanPath, mMetrics, parseFlags);
    ……
    //保存解析后的安装包
    PackageParser.Package scannedPkg = scanPackageLI(pkg, parseFlags, scanMode
            | SCAN_UPDATE_SIGNATURE, currentTime, user);
    ……
    return scannedPkg;
}

其调用了parsePackage用于获取apk中的资源对象res和对Androidmanifest.xml文件进行格式化，并调用另一个parsePackage函数进一步做解析，也是package类真正生成的地方

啥是package？

package类是安卓框架中用于表示一个应用程序包的结构和信息的类。它包含了应用程序的多个方面的信息，包括：

包名：唯一标识应用程序的字符串，通常是反向域名格式（例如，com.example.myapp）。
版本信息：包括应用程序的版本号和版本代码，帮助识别应用的更新和兼容性。

权限：声明应用所需的权限，例如访问互联网、读取联系人等。

组件：描述应用程序包含的组件，如活动（Activity）、服务（Service）、内容提供者（Content Provider）和广播接收器（Broadcast Receiver）。

保存了app的信息之后调用createDataDirsLI进行真正的安装操作

private int createDataDirsLI(String packageName, int uid, String seinfo) {
    int[] users = sUserManager.getUserIds();
    int res = mInstaller.install(packageName, uid, uid, seinfo);
    if (res < 0) {
        return res;
    }
    for (int user : users) {
        if (user != 0) {
            res = mInstaller.createUserData(packageName,
                    UserHandle.getUid(user, uid), user);
            if (res < 0) {
                return res;
            }
        }
    }
    return res;
}

调用了install类的install方法 install调用execute execute调用transaction transaction进行客户端-服务端通信，首先判断客户端-服务端是否连接

然后调用writeCommand向服务端通过socket，向服务端发送指令

如果发送的指令是install 服务端就会调用do_install进行安装 do_install调用了commands.c文件的install函数执行安装

int install(const char *pkgname, uid_t uid, gid_t gid, const char *seinfo)
{
    char pkgdir[PKG_PATH_MAX];  //程序目录路径最长256
    char libsymlink[PKG_PATH_MAX];
    char applibdir[PKG_PATH_MAX];
    struct stat libStat;
    // 权限判断
    if ((uid < AID_SYSTEM) || (gid < AID_SYSTEM)) {
        ALOGE("invalid uid/gid: %d %d\n", uid, gid);
        return -1;
    }
    // 组合应用程序安装目录pkgdir=”/data/data/应用程序包名”
    if (create_pkg_path(pkgdir, pkgname, PKG_DIR_POSTFIX, 0)) {
        ALOGE("cannot create package path\n");
        return -1;
    }
    ……
    // 创建应用程序安装目录pkgdir=”/data/data/应用程序包名”
    if (mkdir(pkgdir, 0751) < 0) {
        ALOGE("cannot create dir '%s': %s\n", pkgdir, strerror(errno));
        return -1;
    }
    // 修改应用程序安装目录pkgdir=”/data/data/应用程序包名”权限
    if (chmod(pkgdir, 0751) < 0) {
        ALOGE("cannot chmod dir '%s': %s\n", pkgdir, strerror(errno));
        unlink(pkgdir);
        return -1;
    }
    ……
    return 0;
}