Android入门之路（含面试经验）

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Apk安装的主要步骤:

为了学习这个过程,真的是陷入了pms的源码很久,也看了很多前人的博文,才算是有了些思路,所以此处先把主要步骤列出来,后面再慢慢分析细节。

  1. 将apk文件复制到data/app目录
  2. 解析apk信息
  3. dexopt操作
  4. 更新权限信息
  5. 完成安装,发送Intent.ACTION_PACKAGE_ADDED广播

下面将具体步骤列张图出来:

由图可见安装过程中流转的步骤还是比较多的,下面具体分析

1. 将apk文件copy至data/app目录

1.1 installPackageAsUser

 mContext.enforceCallingOrSelfPermission(android.Manifest.permission.INSTALL_PACKAGES, null);

        final int callingUid = Binder.getCallingUid();
        ...
        ...

        if ((callingUid == Process.SHELL_UID) || (callingUid == Process.ROOT_UID)) {
            installFlags |= PackageManager.INSTALL_FROM_ADB;

        } else {
            // Caller holds INSTALL_PACKAGES permission, so we're less strict
            // about installerPackageName.

            installFlags &= ~PackageManager.INSTALL_FROM_ADB;
            installFlags &= ~PackageManager.INSTALL_ALL_USERS;
        }

        UserHandle user;
        if ((installFlags & PackageManager.INSTALL_ALL_USERS) != 0) {
            user = UserHandle.ALL;
        } else {
            user = new UserHandle(userId);
        }

        verificationParams.setInstallerUid(callingUid);

        final File originFile = new File(originPath);
        final OriginInfo origin = OriginInfo.fromUntrustedFile(originFile);

        final Message msg = mHandler.obtainMessage(INIT_COPY);
        msg.obj = new InstallParams(origin, observer, installFlags,
                installerPackageName, verificationParams, user, packageAbiOverride);
        mHandler.sendMessage(msg);

这个方法主要是判断安装来源,包括adb,shell,all_user,然后向PMS的mHandler发送INIT_COPY的消息,这个mHandler运行在一个HandlerThread中。

1.2 handleMessage(INIT_COPY)&handleMessage(MCS_BOUND)

case INIT_COPY:{
                    HandlerParams params = (HandlerParams) msg.obj;
                    int idx = mPendingInstalls.size();
                    if (DEBUG_INSTALL) Slog.i(TAG, "init_copy idx=" + idx + ": " + params);
                    // If a bind was already initiated we dont really
                    // need to do anything. The pending install
                    // will be processed later on.
                    if (!mBound) {
                        // If this is the only one pending we might
                        // have to bind to the service again.
                        if (!connectToService()) {
                            Slog.e(TAG, "Failed to bind to media container service");
                            params.serviceError();
                            return;
                        } else {
                            // Once we bind to the service, the first
                            // pending request will be processed.
                            mPendingInstalls.add(idx, params);
                        }
                    } else {
                        mPendingInstalls.add(idx, params);
                        // Already bound to the service. Just make
                        // sure we trigger off processing the first request.
                        if (idx == 0) {
                            mHandler.sendEmptyMessage(MCS_BOUND);
                        }
                    }
}
case MCS_BOUND:{
...
...
 HandlerParams params = mPendingInstalls.get(0);
                        if (params != null) {
                            if (params.startCopy()) {
                                // We are done...  look for more work or to
                                // go idle.
                                if (DEBUG_SD_INSTALL) Log.i(TAG,
                                        "Checking for more work or unbind...");
                                // Delete pending install
                                if (mPendingInstalls.size() > 0) {
                                    mPendingInstalls.remove(0);
                                }
                                if (mPendingInstalls.size() == 0) {
                                    if (mBound) {
                                        if (DEBUG_SD_INSTALL) Log.i(TAG,
                                                "Posting delayed MCS_UNBIND");
                                        removeMessages(MCS_UNBIND);
                                        Message ubmsg = obtainMessage(MCS_UNBIND);
                                        // Unbind after a little delay, to avoid
                                        // continual thrashing.
                                        sendMessageDelayed(ubmsg, 10000);
                                    }
...
...
}

INIT_COPY主要是确保DefaultContainerService已bound,DefaultContainerService是一个应用服务，具体负责实现APK等相关资源文件在内部或外部存储器上的存储工作。而MCS_BOUND中则执行了 params.startCopy()这句,也是最关键的开始copy文件。

1.3 HandlerParams.startCopy

  final boolean startCopy() {
            boolean res;
            try {
                if (DEBUG_INSTALL) Slog.i(TAG, "startCopy " + mUser + ": " + this);

                if (++mRetries > MAX_RETRIES) {
                    Slog.w(TAG, "Failed to invoke remote methods on default container service. Giving up");
                    mHandler.sendEmptyMessage(MCS_GIVE_UP);
                    handleServiceError();
                    return false;
                } else {
                    handleStartCopy();
                    res = true;
                }
            } catch (RemoteException e) {
                if (DEBUG_INSTALL) Slog.i(TAG, "Posting install MCS_RECONNECT");
                mHandler.sendEmptyMessage(MCS_RECONNECT);
                res = false;
            }
            handleReturnCode();
            return res;
        }

该方法中除了检查重试次数外只是简单的调用了handleStartCopy()及handleReturnCode()方法.

1.4 handleStartCopy()

这个方法内容非常多,下面只列出些核心部分

 public void handleStartCopy() throws RemoteException {
           int ret = PackageManager.INSTALL_SUCCEEDED;
            ...
            ...
            final boolean onSd = (installFlags & PackageManager.INSTALL_EXTERNAL) != 0;
            final boolean onInt = (installFlags & PackageManager.INSTALL_INTERNAL) != 0;

            PackageInfoLite pkgLite = null;

            if (onInt && onSd) {
                // Check if both bits are set.
                Slog.w(TAG, "Conflicting flags specified for installing on both internal and external");
                ret = PackageManager.INSTALL_FAILED_INVALID_INSTALL_LOCATION;
            } else {
                pkgLite = mContainerService.getMinimalPackageInfo(origin.resolvedPath, installFlags,
                        packageAbiOverride);

                /*
                 * If we have too little free space, try to free cache
                 * before giving up.
                 */
                if (!origin.staged && pkgLite.recommendedInstallLocation
                        == PackageHelper.RECOMMEND_FAILED_INSUFFICIENT_STORAGE) {
                    final StorageManager storage = StorageManager.from(mContext);
                    final long lowThreshold = storage.getStorageLowBytes(
                            Environment.getDataDirectory());

                    final long sizeBytes = mContainerService.calculateInstalledSize(
                            origin.resolvedPath, isForwardLocked(), packageAbiOverride);

                    if (mInstaller.freeCache(sizeBytes + lowThreshold) >= 0) {
                        pkgLite = mContainerService.getMinimalPackageInfo(origin.resolvedPath,
                                installFlags, packageAbiOverride);
                    }
                }
            }
            ...
            ...
                     * No package verification is enabled, so immediately start
                     * the remote call to initiate copy using temporary file.
                     */
                    ret = args.copyApk(mContainerService, true);

            }
            mRet = ret;
        }

handleStartCopy的核心就是copyApk,其他的都是些存储空间检查,权限检查等等安全校验

2 .解析apk信息

完成apk copy到data/app目录的操作后,下一步就到了 handleReturnCode,这个方法又跳转到processPendingInstall()方法,下面先来看看processPendingInstall()方法:

2.1 processPendingInstall()

    private void processPendingInstall(final InstallArgs args, final int currentStatus) {
        // Queue up an async operation since the package installation may take a little while.
        mHandler.post(new Runnable() {
            public void run() {
                mHandler.removeCallbacks(this);
                 // Result object to be returned
                PackageInstalledInfo res = new PackageInstalledInfo();
                res.returnCode = currentStatus;
                res.uid = -1;
                res.pkg = null;
                res.removedInfo = new PackageRemovedInfo();
                if (res.returnCode == PackageManager.INSTALL_SUCCEEDED) {
                    args.doPreInstall(res.returnCode);
                    synchronized (mInstallLock) {
                        installPackageLI(args, res); //1.安装
                    }
                    args.doPostInstall(res.returnCode, res.uid);
                }

                // A restore should be performed at this point if (a) the install
                // succeeded, (b) the operation is not an update, and (c) the new
                // package has not opted out of backup participation.
                final boolean update = res.removedInfo.removedPackage != null;
                final int flags = (res.pkg == null) ? 0 : res.pkg.applicationInfo.flags;
                boolean doRestore = !update
                        && ((flags & ApplicationInfo.FLAG_ALLOW_BACKUP) != 0);

                // Set up the post-install work request bookkeeping.  This will be used
                // and cleaned up by the post-install event handling regardless of whether
                // there's a restore pass performed.  Token values are >= 1.
                int token;
                if (mNextInstallToken < 0) mNextInstallToken = 1;
                token = mNextInstallToken++;

                PostInstallData data = new PostInstallData(args, res);
                mRunningInstalls.put(token, data);
                if (DEBUG_INSTALL) Log.v(TAG, "+ starting restore round-trip " + token);

                if (res.returnCode == PackageManager.INSTALL_SUCCEEDED && doRestore) {
                    // Pass responsibility to the Backup Manager.  It will perform a
                    // restore if appropriate, then pass responsibility back to the
                    // Package Manager to run the post-install observer callbacks
                    // and broadcasts.
                    IBackupManager bm = IBackupManager.Stub.asInterface(
                            ServiceManager.getService(Context.BACKUP_SERVICE));
                    if (bm != null) {
                        if (DEBUG_INSTALL) Log.v(TAG, "token " + token
                                + " to BM for possible restore");
                        try {
                            bm.restoreAtInstall(res.pkg.applicationInfo.packageName, token); //2.调用backup服务
                        } catch (RemoteException e) {
                            // can't happen; the backup manager is local
                        } catch (Exception e) {
                            Slog.e(TAG, "Exception trying to enqueue restore", e);
                            doRestore = false;
                        }
                    } else {
                        Slog.e(TAG, "Backup Manager not found!");
                        doRestore = false;
                    }
                }

                if (!doRestore) {
                    // No restore possible, or the Backup Manager was mysteriously not
                    // available -- just fire the post-install work request directly.
                    if (DEBUG_INSTALL) Log.v(TAG, "No restore - queue post-install for " + token);
                    Message msg = mHandler.obtainMessage(POST_INSTALL, token, 0);
                    mHandler.sendMessage(msg);
                }
            }
        });
    }

这个方法有几个关键步骤,一是installPackageLI(args, res);,这个方法具体执行了解析package和后续操作,而再installPackageLI(args, res);执行完毕后会走到bm.restoreAtInstall(res.pkg.applicationInfo.packageName, token);,会调用backupservice的restoreAtInstall方法,而restoreAtInstall方法最终又会调用PMS的finishPackageInstall()方法,完成安装。

2.2 installPackageLI(args, res)

private void installPackageLI(InstallArgs args, PackageInstalledInfo res) {
        final int installFlags = args.installFlags;
        String installerPackageName = args.installerPackageName;
        File tmpPackageFile = new File(args.getCodePath());
        boolean forwardLocked = ((installFlags & PackageManager.INSTALL_FORWARD_LOCK) != 0);
        boolean onSd = ((installFlags & PackageManager.INSTALL_EXTERNAL) != 0);
        boolean replace = false;
        final int scanFlags = SCAN_NEW_INSTALL | SCAN_FORCE_DEX | SCAN_UPDATE_SIGNATURE;
        // Result object to be returned
        res.returnCode = PackageManager.INSTALL_SUCCEEDED;

        if (DEBUG_INSTALL) Slog.d(TAG, "installPackageLI: path=" + tmpPackageFile);
        // Retrieve PackageSettings and parse package
        final int parseFlags = mDefParseFlags | PackageParser.PARSE_CHATTY
                | (forwardLocked ? PackageParser.PARSE_FORWARD_LOCK : 0)
                | (onSd ? PackageParser.PARSE_ON_SDCARD : 0);
        PackageParser pp = new PackageParser();
        pp.setSeparateProcesses(mSeparateProcesses);
        pp.setDisplayMetrics(mMetrics);

        final PackageParser.Package pkg;
        try {
            pkg = pp.parsePackage(tmpPackageFile, parseFlags);
        } catch (PackageParserException e) {
            res.setError("Failed parse during installPackageLI", e);
            return;
        }

        // Mark that we have an install time CPU ABI override.
        pkg.cpuAbiOverride = args.abiOverride;

        String pkgName = res.name = pkg.packageName;
        if ((pkg.applicationInfo.flags&ApplicationInfo.FLAG_TEST_ONLY) != 0) {
            if ((installFlags & PackageManager.INSTALL_ALLOW_TEST) == 0) {
                res.setError(INSTALL_FAILED_TEST_ONLY, "installPackageLI");
                return;
            }
        }

        try {
            pp.collectCertificates(pkg, parseFlags);
            pp.collectManifestDigest(pkg);
        } catch (PackageParserException e) {
            res.setError("Failed collect during installPackageLI", e);
            return;
        }

        /* If the installer passed in a manifest digest, compare it now. */
        if (args.manifestDigest != null) {
            if (DEBUG_INSTALL) {
                final String parsedManifest = pkg.manifestDigest == null ? "null"
                        : pkg.manifestDigest.toString();
                Slog.d(TAG, "Comparing manifests: " + args.manifestDigest.toString() + " vs. "
                        + parsedManifest);
            }

            if (!args.manifestDigest.equals(pkg.manifestDigest)) {
                res.setError(INSTALL_FAILED_PACKAGE_CHANGED, "Manifest digest changed");
                return;
            }
        } else if (DEBUG_INSTALL) {
            final String parsedManifest = pkg.manifestDigest == null
                    ? "null" : pkg.manifestDigest.toString();
            Slog.d(TAG, "manifestDigest was not present, but parser got: " + parsedManifest);
        }

        // Get rid of all references to package scan path via parser.
        pp = null;
        String oldCodePath = null;
        boolean systemApp = false;
        synchronized (mPackages) {
            // Check whether the newly-scanned package wants to define an already-defined perm
            int N = pkg.permissions.size();
            for (int i = N-1; i >= 0; i--) {
                PackageParser.Permission perm = pkg.permissions.get(i);
                BasePermission bp = mSettings.mPermissions.get(perm.info.name);
                if (bp != null) {
                    // If the defining package is signed with our cert, it's okay.  This
                    // also includes the "updating the same package" case, of course.
                    // "updating same package" could also involve key-rotation.
                    final boolean sigsOk;
                    if (!bp.sourcePackage.equals(pkg.packageName)
                            || !(bp.packageSetting instanceof PackageSetting)
                            || !bp.packageSetting.keySetData.isUsingUpgradeKeySets()
                            || ((PackageSetting) bp.packageSetting).sharedUser != null) {
                        sigsOk = compareSignatures(bp.packageSetting.signatures.mSignatures,
                                pkg.mSignatures) == PackageManager.SIGNATURE_MATCH;
                    } else {
                        sigsOk = checkUpgradeKeySetLP((PackageSetting) bp.packageSetting, pkg);
                    }
                    if (!sigsOk) {
                        // If the owning package is the system itself, we log but allow
                        // install to proceed; we fail the install on all other permission
                        // redefinitions.
                        if (!bp.sourcePackage.equals("android")) {
                            res.setError(INSTALL_FAILED_DUPLICATE_PERMISSION, "Package "
                                    + pkg.packageName + " attempting to redeclare permission "
                                    + perm.info.name + " already owned by " + bp.sourcePackage);
                            res.origPermission = perm.info.name;
                            res.origPackage = bp.sourcePackage;
                            return;
                        } else {
                            Slog.w(TAG, "Package " + pkg.packageName
                                    + " attempting to redeclare system permission "
                                    + perm.info.name + "; ignoring new declaration");
                            pkg.permissions.remove(i);
                        }
                    }
                }
            }

            // Check if installing already existing package
            if ((installFlags & PackageManager.INSTALL_REPLACE_EXISTING) != 0) {
                String oldName = mSettings.mRenamedPackages.get(pkgName);
                if (pkg.mOriginalPackages != null
                        && pkg.mOriginalPackages.contains(oldName)
                        && mPackages.containsKey(oldName)) {
                    // This package is derived from an original package,
                    // and this device has been updating from that original
                    // name.  We must continue using the original name, so
                    // rename the new package here.
                    pkg.setPackageName(oldName);
                    pkgName = pkg.packageName;
                    replace = true;
                    if (DEBUG_INSTALL) Slog.d(TAG, "Replacing existing renamed package: oldName="
                            + oldName + " pkgName=" + pkgName);
                } else if (mPackages.containsKey(pkgName)) {
                    // This package, under its official name, already exists
                    // on the device; we should replace it.
                    replace = true;
                    if (DEBUG_INSTALL) Slog.d(TAG, "Replace existing pacakge: " + pkgName);
                }
            }
            PackageSetting ps = mSettings.mPackages.get(pkgName);
            if (ps != null) {
                if (DEBUG_INSTALL) Slog.d(TAG, "Existing package: " + ps);
                oldCodePath = mSettings.mPackages.get(pkgName).codePathString;
                if (ps.pkg != null && ps.pkg.applicationInfo != null) {
                    systemApp = (ps.pkg.applicationInfo.flags &
                            ApplicationInfo.FLAG_SYSTEM) != 0;
                }
                res.origUsers = ps.queryInstalledUsers(sUserManager.getUserIds(), true);
            }
        }

        if (systemApp && onSd) {
            // Disable updates to system apps on sdcard
            res.setError(INSTALL_FAILED_INVALID_INSTALL_LOCATION,
                    "Cannot install updates to system apps on sdcard");
            return;
        }

        if (!args.doRename(res.returnCode, pkg, oldCodePath)) {
            res.setError(INSTALL_FAILED_INSUFFICIENT_STORAGE, "Failed rename");
            return;
        }

        if (replace) {
            replacePackageLI(pkg, parseFlags, scanFlags | SCAN_REPLACING, args.user,
                    installerPackageName, res);
        } else {
            installNewPackageLI(pkg, parseFlags, scanFlags | SCAN_DELETE_DATA_ON_FAILURES,
                    args.user, installerPackageName, res);
        }
        synchronized (mPackages) {
            final PackageSetting ps = mSettings.mPackages.get(pkgName);
            if (ps != null) {
                res.newUsers = ps.queryInstalledUsers(sUserManager.getUserIds(), true);
            }
        }
    }

这个方法先是解析了package包,然后做了大量签名和权限校验的工作,最终会走到

  if (replace) {
            replacePackageLI(pkg, parseFlags, scanFlags | SCAN_REPLACING, args.user,
                    installerPackageName, res);
        } else {
            installNewPackageLI(pkg, parseFlags, scanFlags | SCAN_DELETE_DATA_ON_FAILURES,
                    args.user, installerPackageName, res);
        }

这两个方法分别是覆盖安装和安装新应用对应的具体执行.我们来看看installNewPackageLI()

2.3 installNewPackageLI()

    private void installNewPackageLI(PackageParser.Package pkg,
            int parseFlags, int scanFlags, UserHandle user,
            String installerPackageName, PackageInstalledInfo res) {
        // Remember this for later, in case we need to rollback this install
        String pkgName = pkg.packageName;

        if (DEBUG_INSTALL) Slog.d(TAG, "installNewPackageLI: " + pkg);
        boolean dataDirExists = getDataPathForPackage(pkg.packageName, 0).exists();
        synchronized(mPackages) {
            if (mSettings.mRenamedPackages.containsKey(pkgName)) {
                // A package with the same name is already installed, though
                // it has been renamed to an older name.  The package we
                // are trying to install should be installed as an update to
                // the existing one, but that has not been requested, so bail.
                res.setError(INSTALL_FAILED_ALREADY_EXISTS, "Attempt to re-install " + pkgName
                        + " without first uninstalling package running as "
                        + mSettings.mRenamedPackages.get(pkgName));
                return;
            }
            if (mPackages.containsKey(pkgName)) {
                // Don't allow installation over an existing package with the same name.
                res.setError(INSTALL_FAILED_ALREADY_EXISTS, "Attempt to re-install " + pkgName
                        + " without first uninstalling.");
                return;
            }
        }

        try {
            PackageParser.Package newPackage = scanPackageLI(pkg, parseFlags, scanFlags,
                    System.currentTimeMillis(), user);

            updateSettingsLI(newPackage, installerPackageName, null, null, res);
            // delete the partially installed application. the data directory will have to be
            // restored if it was already existing
            if (res.returnCode != PackageManager.INSTALL_SUCCEEDED) {
                // remove package from internal structures.  Note that we want deletePackageX to
                // delete the package data and cache directories that it created in
                // scanPackageLocked, unless those directories existed before we even tried to
                // install.
                deletePackageLI(pkgName, UserHandle.ALL, false, null, null,
                        dataDirExists ? PackageManager.DELETE_KEEP_DATA : 0,
                                res.removedInfo, true);
            }

        } catch (PackageManagerException e) {
            res.setError("Package couldn't be installed in " + pkg.codePath, e);
        }
    }

这个方法核心的步骤有两个:

  • PackageParser.Package newPackage = scanPackageLI(pkg, parseFlags, scanFlags,System.currentTimeMillis(), user);
  • updateSettingsLI(newPackage, installerPackageName, null, null, res);

scanPackageLI负责安装,而updateSettingLI则是完成安装后的设置信息更新

2.4 scanPackageLI()

scanPackageLI()方法主要逻辑是由scanPackageDirtyLI()实现的,scanPackageDirtyLI()实在太长了,此处就不列出了,主要说下,这个方法实现了以下操作:

  • 设置系统App的一些参数
  • 校验签名
  • 解析app的provider,校验是否与已有的provider冲突
  • 32/64位abi的一些设置
  • 四大组件的解析，注册

scanPackageDirtyLI()里面的操作确实是太多了，并不止这几点。如需更详细的信息还请查看源码。

另一方面，这个方法里,会调用到performDexOptLI(),其会去执行dexopt操作。

3. dexopt操作

Apk文件其实只是一个归档zip压缩包,而我们编写的代码最终都编译成了.dex文件,但为了提高运行性能,android系统并不会直接执行.dex,而是会在安装过程中执行dexopt操作来优化.dex文件,最终android系统执行的时优化后的'odex'文件(注意:这个odex文件的后缀也是.dex,其路径在data/dalvik-cache)。对于dalvik虚拟机,dexopt就是优化操作,而对于art虚拟机,dexopt执行的则是dex2oat操作,既将.dex文件翻译成oat文件。关于art和dex2oat的更多信息请看后文。

这里我们先来看看PMS的dexopt操作:

3.1 performDexOptLI()

这个方法的核心是

final int ret = mInstaller.dexopt(path, sharedGid, !isForwardLocked(pkg), pkg.packageName, dexCodeInstructionSet, vmSafeMode);

其作用就是调用PMS的mInstaller成员变量的dexopt操作。

3.2 Installer.dexopt

Installer类的dexopt方法又调用InstallerConnection类的dexopt方法,来看看这个方法:

public int dexopt(String apkPath, int uid, boolean isPublic, String pkgName,
            String instructionSet, boolean vmSafeMode) {
        StringBuilder builder = new StringBuilder("dexopt");
        builder.append(' ');
        builder.append(apkPath);
        builder.append(' ');
        builder.append(uid);
        builder.append(isPublic ? " 1" : " 0");
        builder.append(' ');
        builder.append(pkgName);
        builder.append(' ');
        builder.append(instructionSet);
        builder.append(' ');
        builder.append(vmSafeMode ? " 1" : " 0");
        return execute(builder.toString());
    }
 public synchronized String transact(String cmd) {
        if (!connect()) {
            Slog.e(TAG, "connection failed");
            return "-1";
        }

        if (!writeCommand(cmd)) {
            /*
             * If installd died and restarted in the background (unlikely but
             * possible) we'll fail on the next write (this one). Try to
             * reconnect and write the command one more time before giving up.
             */
            Slog.e(TAG, "write command failed? reconnect!");
            if (!connect() || !writeCommand(cmd)) {
                return "-1";
            }
        }
        if (LOCAL_DEBUG) {
            Slog.i(TAG, "send: '" + cmd + "'");
        }

        final int replyLength = readReply();
        if (replyLength > 0) {
            String s = new String(buf, 0, replyLength);
            if (LOCAL_DEBUG) {
                Slog.i(TAG, "recv: '" + s + "'");
            }
            return s;
        } else {
            if (LOCAL_DEBUG) {
                Slog.i(TAG, "fail");
            }
            return "-1";
        }
    }

    public int execute(String cmd) {
        String res = transact(cmd);
        try {
            return Integer.parseInt(res);
        } catch (NumberFormatException ex) {
            return -1;
        }
    }
  private boolean connect() {
        if (mSocket != null) {
            return true;
        }
        Slog.i(TAG, "connecting...");
        try {
            mSocket = new LocalSocket();

            LocalSocketAddress address = new LocalSocketAddress("installd",
                    LocalSocketAddress.Namespace.RESERVED);

            mSocket.connect(address);

            mIn = mSocket.getInputStream();
            mOut = mSocket.getOutputStream();
        } catch (IOException ex) {
            disconnect();
            return false;
        }
        return true;
    }

由上面的几个方法可以知道,最终dexopt操作是通过socket的方式来跨进程通知守护进程installd,由其去执行dexopt操作。

3.3 commands::dexopt()

最终守护进程installd会调用Commands.c文件(位于/source/framework/native/cmds/installd)的dexopt方法。

int dexopt(const char *apk_path, uid_t uid, bool is_public,
           const char *pkgname, const char *instruction_set,
           bool vm_safe_mode, bool is_patchoat)
{
    struct utimbuf ut;
    struct stat input_stat, dex_stat;
    char out_path[PKG_PATH_MAX];
    char persist_sys_dalvik_vm_lib[PROPERTY_VALUE_MAX];
    char *end;
    const char *input_file;
    char in_odex_path[PKG_PATH_MAX];
    int res, input_fd=-1, out_fd=-1;

    ...
    ...

    pid_t pid;
    pid = fork();
    if (pid == 0) {
        /* child -- drop privileges before continuing */
        if (setgid(uid) != 0) {
            ALOGE("setgid(%d) failed in installd during dexopt\n", uid);
            exit(64);
        }
        if (setuid(uid) != 0) {
            ALOGE("setuid(%d) failed in installd during dexopt\n", uid);
            exit(65);
        }
        // drop capabilities
        struct __user_cap_header_struct capheader;
        struct __user_cap_data_struct capdata[2];
        memset(&capheader, 0, sizeof(capheader));
        memset(&capdata, 0, sizeof(capdata));
        capheader.version = _LINUX_CAPABILITY_VERSION_3;
        if (capset(&capheader, &capdata[0]) < 0) {
            ALOGE("capset failed: %s\n", strerror(errno));
            exit(66);
        }
        if (set_sched_policy(0, SP_BACKGROUND) < 0) {
            ALOGE("set_sched_policy failed: %s\n", strerror(errno));
            exit(70);
        }
        if (flock(out_fd, LOCK_EX | LOCK_NB) != 0) {
            ALOGE("flock(%s) failed: %s\n", out_path, strerror(errno));
            exit(67);
        }

        if (strncmp(persist_sys_dalvik_vm_lib, "libdvm", 6) == 0) {
            run_dexopt(input_fd, out_fd, input_file, out_path);
        } else if (strncmp(persist_sys_dalvik_vm_lib, "libart", 6) == 0) {
            if (is_patchoat) {
                run_patchoat(input_fd, out_fd, input_file, out_path, pkgname, instruction_set);
            } else {
                run_dex2oat(input_fd, out_fd, input_file, out_path, pkgname, instruction_set,
                            vm_safe_mode);
            }
        } else {
            exit(69);   /* Unexpected persist.sys.dalvik.vm.lib value */
        }
        exit(68);   /* only get here on exec failure */
    } else {
        res = wait_child(pid);
        if (res == 0) {
            ALOGV("DexInv: --- END '%s' (success) ---\n", input_file);
        } else {
            ALOGE("DexInv: --- END '%s' --- status=0x%04x, process failed\n", input_file, res);
            goto fail;
        }
    }

    ut.actime = input_stat.st_atime;
    ut.modtime = input_stat.st_mtime;
    utime(out_path, &ut);

    close(out_fd);
    close(input_fd);
    return 0;

fail:
    if (out_fd >= 0) {
        close(out_fd);
        unlink(out_path);
    }
    if (input_fd >= 0) {
        close(input_fd);
    }
    return -1;
}

由上面的代码可以发现,installd在做了些操作后,fork出了一个新的进程,根据虚拟机的类型为libdvm或libart分别执行run_dexopt或run_dex2oat(如果为is_patchoat,则是run_patchoat)操作。

4. 更新权限信息

dexopt操作执行完后,installNewPackageLI()方法就会走到updateSettingsLI()来更新设置信息,而更新设置信息主要是权限信息,所以直接来看updatePermissionsLPw();

4.1 updatePermissionsLPw

private void updatePermissionsLPw(String changingPkg,
            PackageParser.Package pkgInfo, int flags) {
        // Make sure there are no dangling permission trees.
        Iterator<BasePermission> it = mSettings.mPermissionTrees.values().iterator();
        while (it.hasNext()) {
            final BasePermission bp = it.next();
            if (bp.packageSetting == null) {
                // We may not yet have parsed the package, so just see if
                // we still know about its settings.
                bp.packageSetting = mSettings.mPackages.get(bp.sourcePackage);
            }
            if (bp.packageSetting == null) {
                Slog.w(TAG, "Removing dangling permission tree: " + bp.name
                        + " from package " + bp.sourcePackage);
                it.remove();
            } else if (changingPkg != null && changingPkg.equals(bp.sourcePackage)) {
                if (pkgInfo == null || !hasPermission(pkgInfo, bp.name)) {
                    Slog.i(TAG, "Removing old permission tree: " + bp.name
                            + " from package " + bp.sourcePackage);
                    flags |= UPDATE_PERMISSIONS_ALL;
                    it.remove();
                }
            }
        }

        // Make sure all dynamic permissions have been assigned to a package,
        // and make sure there are no dangling permissions.
        it = mSettings.mPermissions.values().iterator();
        while (it.hasNext()) {
            final BasePermission bp = it.next();
            if (bp.type == BasePermission.TYPE_DYNAMIC) {
                if (DEBUG_SETTINGS) Log.v(TAG, "Dynamic permission: name="
                        + bp.name + " pkg=" + bp.sourcePackage
                        + " info=" + bp.pendingInfo);
                if (bp.packageSetting == null && bp.pendingInfo != null) {
                    final BasePermission tree = findPermissionTreeLP(bp.name);
                    if (tree != null && tree.perm != null) {
                        bp.packageSetting = tree.packageSetting;
                        bp.perm = new PackageParser.Permission(tree.perm.owner,
                                new PermissionInfo(bp.pendingInfo));
                        bp.perm.info.packageName = tree.perm.info.packageName;
                        bp.perm.info.name = bp.name;
                        bp.uid = tree.uid;
                    }
                }
            }
            if (bp.packageSetting == null) {
                // We may not yet have parsed the package, so just see if
                // we still know about its settings.
                bp.packageSetting = mSettings.mPackages.get(bp.sourcePackage);
            }
            if (bp.packageSetting == null) {
                Slog.w(TAG, "Removing dangling permission: " + bp.name
                        + " from package " + bp.sourcePackage);
                it.remove();
            } else if (changingPkg != null && changingPkg.equals(bp.sourcePackage)) {
                if (pkgInfo == null || !hasPermission(pkgInfo, bp.name)) {
                    Slog.i(TAG, "Removing old permission: " + bp.name
                            + " from package " + bp.sourcePackage);
                    flags |= UPDATE_PERMISSIONS_ALL;
                    it.remove();
                }
            }
        }

        // Now update the permissions for all packages, in particular
        // replace the granted permissions of the system packages.
        if ((flags&UPDATE_PERMISSIONS_ALL) != 0) {
            for (PackageParser.Package pkg : mPackages.values()) {
                if (pkg != pkgInfo) {
                    grantPermissionsLPw(pkg, (flags&UPDATE_PERMISSIONS_REPLACE_ALL) != 0,
                            changingPkg);
                }
            }
        }

        if (pkgInfo != null) {
            grantPermissionsLPw(pkgInfo, (flags&UPDATE_PERMISSIONS_REPLACE_PKG) != 0, changingPkg);
        }
    }


    private void grantPermissionsLPw(PackageParser.Package pkg, boolean replace,
            String packageOfInterest) {
        final PackageSetting ps = (PackageSetting) pkg.mExtras;
        if (ps == null) {
            return;
        }
        final GrantedPermissions gp = ps.sharedUser != null ? ps.sharedUser : ps;
        HashSet<String> origPermissions = gp.grantedPermissions;
        boolean changedPermission = false;

        if (replace) {
            ps.permissionsFixed = false;
            if (gp == ps) {
                origPermissions = new HashSet<String>(gp.grantedPermissions);
                gp.grantedPermissions.clear();
                gp.gids = mGlobalGids;
            }
        }

        if (gp.gids == null) {
            gp.gids = mGlobalGids;
        }

        final int N = pkg.requestedPermissions.size();
        for (int i=0; i<N; i++) {
            final String name = pkg.requestedPermissions.get(i);
            final boolean required = pkg.requestedPermissionsRequired.get(i);
            final BasePermission bp = mSettings.mPermissions.get(name);
            if (DEBUG_INSTALL) {
                if (gp != ps) {
                    Log.i(TAG, "Package " + pkg.packageName + " checking " + name + ": " + bp);
                }
            }

            if (bp == null || bp.packageSetting == null) {
                if (packageOfInterest == null || packageOfInterest.equals(pkg.packageName)) {
                    Slog.w(TAG, "Unknown permission " + name
                            + " in package " + pkg.packageName);
                }
                continue;
            }

            final String perm = bp.name;
            boolean allowed;
            boolean allowedSig = false;
            if ((bp.protectionLevel&PermissionInfo.PROTECTION_FLAG_APPOP) != 0) {
                // Keep track of app op permissions.
                ArraySet<String> pkgs = mAppOpPermissionPackages.get(bp.name);
                if (pkgs == null) {
                    pkgs = new ArraySet<>();
                    mAppOpPermissionPackages.put(bp.name, pkgs);
                }
                pkgs.add(pkg.packageName);
            }
            final int level = bp.protectionLevel & PermissionInfo.PROTECTION_MASK_BASE;
            if (level == PermissionInfo.PROTECTION_NORMAL
                    || level == PermissionInfo.PROTECTION_DANGEROUS) {
                // We grant a normal or dangerous permission if any of the following
                // are true:
                // 1) The permission is required
                // 2) The permission is optional, but was granted in the past
                // 3) The permission is optional, but was requested by an
                //    app in /system (not /data)
                //
                // Otherwise, reject the permission.
                allowed = (required || origPermissions.contains(perm)
                        || (isSystemApp(ps) && !isUpdatedSystemApp(ps)));
            } else if (bp.packageSetting == null) {
                // This permission is invalid; skip it.
                allowed = false;
            } else if (level == PermissionInfo.PROTECTION_SIGNATURE) {
                allowed = grantSignaturePermission(perm, pkg, bp, origPermissions);
                if (allowed) {
                    allowedSig = true;
                }
            } else {
                allowed = false;
            }
            if (DEBUG_INSTALL) {
                if (gp != ps) {
                    Log.i(TAG, "Package " + pkg.packageName + " granting " + perm);
                }
            }
            if (allowed) {
                if (!isSystemApp(ps) && ps.permissionsFixed) {
                    // If this is an existing, non-system package, then
                    // we can't add any new permissions to it.
                    if (!allowedSig && !gp.grantedPermissions.contains(perm)) {
                        // Except...  if this is a permission that was added
                        // to the platform (note: need to only do this when
                        // updating the platform).
                        allowed = isNewPlatformPermissionForPackage(perm, pkg);
                    }
                }
                if (allowed) {
                    if (!gp.grantedPermissions.contains(perm)) {
                        changedPermission = true;
                        gp.grantedPermissions.add(perm);
                        gp.gids = appendInts(gp.gids, bp.gids);
                    } else if (!ps.haveGids) {
                        gp.gids = appendInts(gp.gids, bp.gids);
                    }
                } else {
                    if (packageOfInterest == null || packageOfInterest.equals(pkg.packageName)) {
                        Slog.w(TAG, "Not granting permission " + perm
                                + " to package " + pkg.packageName
                                + " because it was previously installed without");
                    }
                }
            } else {
                if (gp.grantedPermissions.remove(perm)) {
                    changedPermission = true;
                    gp.gids = removeInts(gp.gids, bp.gids);
                    Slog.i(TAG, "Un-granting permission " + perm
                            + " from package " + pkg.packageName
                            + " (protectionLevel=" + bp.protectionLevel
                            + " flags=0x" + Integer.toHexString(pkg.applicationInfo.flags)
                            + ")");
                } else if ((bp.protectionLevel&PermissionInfo.PROTECTION_FLAG_APPOP) == 0) {
                    // Don't print warning for app op permissions, since it is fine for them
                    // not to be granted, there is a UI for the user to decide.
                    if (packageOfInterest == null || packageOfInterest.equals(pkg.packageName)) {
                        Slog.w(TAG, "Not granting permission " + perm
                                + " to package " + pkg.packageName
                                + " (protectionLevel=" + bp.protectionLevel
                                + " flags=0x" + Integer.toHexString(pkg.applicationInfo.flags)
                                + ")");
                    }
                }
            }
        }

        if ((changedPermission || replace) && !ps.permissionsFixed &&
                !isSystemApp(ps) || isUpdatedSystemApp(ps)){
            // This is the first that we have heard about this package, so the
            // permissions we have now selected are fixed until explicitly
            // changed.
            ps.permissionsFixed = true;
        }
        ps.haveGids = true;
    }

由上面两个方法可以看到,在apk的安装时PMS会将该app的所有权限都记录下来并更新到PMS的mAppOpPermissionPackages成员变量里面,并判定是否授予该app请求的权限。

4.2 完成安装

还记得前面说过的在processPendingInstall方法在执行installPackageLi后会执行以下语句

 if (res.returnCode == PackageManager.INSTALL_SUCCEEDED && doRestore) {
                    // Pass responsibility to the Backup Manager.  It will perform a
                    // restore if appropriate, then pass responsibility back to the
                    // Package Manager to run the post-install observer callbacks
                    // and broadcasts.
                    IBackupManager bm = IBackupManager.Stub.asInterface(
                            ServiceManager.getService(Context.BACKUP_SERVICE));
                    if (bm != null) {
                        if (DEBUG_INSTALL) Log.v(TAG, "token " + token
                                + " to BM for possible restore");
                        try {
                            bm.restoreAtInstall(res.pkg.applicationInfo.packageName, token);
                        } catch (RemoteException e) {
                            // can't happen; the backup manager is local
                        } catch (Exception e) {
                            Slog.e(TAG, "Exception trying to enqueue restore", e);
                            doRestore = false;
                        }
                    } else {
                        Slog.e(TAG, "Backup Manager not found!");
                        doRestore = false;
                    }
                }

我也不是很清楚为什么系统会调用IBackupManager的restoreAtInstall方法,不过发现在BackupManagerService的restoreAtInstall方法中会有以下代码:

...
 if (skip) {
            // Auto-restore disabled or no way to attempt a restore; just tell the Package
            // Manager to proceed with the post-install handling for this package.
            if (DEBUG) Slog.v(TAG, "Finishing install immediately");
            try {
                mPackageManagerBinder.finishPackageInstall(token);
            } catch (RemoteException e) { /* can't happen */ }
        }
...

最终restoreAtInstall方法又会调用PMS的finishPackageInstall方法,而此方法最终会发送Intent.ACTION_PACKAGE_ADDED广播，apk的安装就到到此结束了。