PackageManagerService分析

最新推荐文章于 2021-08-10 13:01:13 发布

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最新推荐文章于 2021-08-10 13:01:13 发布

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本文链接：https://blog.youkuaiyun.com/DaHeMaDeGeGe/article/details/51005376

本文详细解析了Android系统中PackageManagerService的启动流程，从Settings类的初始化开始，介绍了其负责保存与PackageManagerService相关的设置，再到SystemServer如何调用PackageManagerService的主要方法。分析了五个关键文件的作用，包括记录应用信息的packages.xml及其备份文件等。

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在分析PackageManagerService中main()之前,先分析Settings类.这个类用来保存和PackageManagerService相关的一些设置.先来看看Settings类的方法,代码如下

    Settings(Object lock) {
        this(Environment.getDataDirectory(), lock);
    }

    Settings(File dataDir, Object lock) {
        mLock = lock;

        mRuntimePermissionsPersistence = new RuntimePermissionPersistence(mLock);

        mSystemDir = new File(dataDir, "system");
        mSystemDir.mkdirs();
        FileUtils.setPermissions(mSystemDir.toString(),
                FileUtils.S_IRWXU|FileUtils.S_IRWXG
                |FileUtils.S_IROTH|FileUtils.S_IXOTH,
                -1, -1);
        mSettingsFilename = new File(mSystemDir, "packages.xml");
        mBackupSettingsFilename = new File(mSystemDir, "packages-backup.xml");
        mPackageListFilename = new File(mSystemDir, "packages.list");
        FileUtils.setPermissions(mPackageListFilename, 0640, SYSTEM_UID, PACKAGE_INFO_GID);

        // Deprecated: Needed for migration
        mStoppedPackagesFilename = new File(mSystemDir, "packages-stopped.xml");
        mBackupStoppedPackagesFilename = new File(mSystemDir, "packages-stopped-backup.xml");
    }

以上的方法主要作用是创建了5个位于data/system/目录下的File对象.

1)packages.xml: 记录系统中所有安装的应用信息,包括基本信息,签名和权限.

2)packagers-backup.xml:是packages.xml文件的备份.

3)packagers-stopped.xml:记录系统中被强制停止运行的应用信息.系统在强制停止某个应用时,会将应用的信息记录到改文件中.

4)packagers-stopped-backup.xml:是packagers-stopped.xml备份.

5)packages.list:保存普通应用的数据目录和uid等信息.

分析完Settings.java的一些基本信息,我们来分析下PackageManagerService.java的初始化基本过程

Step 1 :

这个函数定义在frameworks/base/services/java/com/android/server/SystemServer.java文件中

    /**
     * Starts a miscellaneous grab bag of stuff that has yet to be refactored
     * and organized.
     */
private void startOtherServices() {
       ....
        try {
            mPackageManagerService.performBootDexOpt();
        } catch (Throwable e) {
            reportWtf("performing boot dexopt", e);
        }
     ...
     try {
            mPackageManagerService.systemReady();
        } catch (Throwable e) {
            reportWtf("making Package Manager Service ready", e);
        }
    }

 private void startBootstrapServices() {
        ....
        // Start the package manager.
        Slog.i(TAG, "Package Manager");
        mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
                mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
        mFirstBoot = mPackageManagerService.isFirstBoot();
        mPackageManager = mSystemContext.getPackageManager();

       ...
        startSensorService();
    }

通过以上代码可以看出,SystemServer对PackagerManagerService的初始化主要通过上面的代码来完成的,接下来我们来分析下PackagerManagerService的main初始化过程.

Step 2:

这个文件定义在frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java中

    public static PackageManagerService main(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        PackageManagerService m;
        if (FeatureConfig.INTEL_FEATURE_PARALLEL_SCAN) {
            int taskNum = SystemProperties.getInt("persist.pms.tasknum",
                    Runtime.getRuntime().availableProcessors()*2);
            m = new PackageManagerService(context, installer,
                    factoryTest, onlyCore, taskNum);
        } else {
            m = new PackageManagerService(context, installer,
                    factoryTest, onlyCore);
        }
        ServiceManager.addService("package", m);
        return m;
    }

通过以上代码看出,main的方法比较简单,主要是创建了PackageManagerService对象并在ServiceManager注册.