1、开篇
在上一篇文章中提到Settings类会在PackageManagerService启动过程中对packages.xml等一些列xml文件进行解析。那么有以下问题：
- 这些文件记录了什么内容？
- 为什么需要这些文件？
让我们一起通过阅读源码解决这些问题吧。
2、packages.xml文件详解
要在真机上拿到packages.xml殊为不易，所以我这里是在模拟器上通过adb命令拉取了一份：
adb pull /data/system/packages.xml
文件内容精简后如下：
<?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<packages>
<version sdkVersion="24" databaseVersion="3" fingerprint="Android/sdk_phone_x86/generic_x86:7.0/NYC/4174735:userdebug/test-keys" />
<version volumeUuid="primary_physical" sdkVersion="24" databaseVersion="3" fingerprint="Android/sdk_phone_x86/generic_x86:7.0/NYC/4174735:userdebug/test-keys" />
<permission-trees />
<permissions>
<item name="android.permission.REAL_GET_TASKS" package="android" protection="18" />
<item name="android.permission.ACCESS_CACHE_FILESYSTEM" package="android" protection="18" />
...
</permissions>
<package name="com.android.providers.media" codePath="/system/priv-app/MediaProvider" nativeLibraryPath="/system/priv-app/MediaProvider/lib" primaryCpuAbi="x86" publicFlags="944291397" privateFlags="8" ft="15d38697a58" it="15d38697a58" ut="15d38697a58" version="800" sharedUserId="10010">
<sigs count="1">
<cert index="2" key="308..." />
</sigs>
<perms>
<item name="android.permission.ACCESS_CACHE_FILESYSTEM" granted="true" flags="0" />
...
</perms>
<proper-signing-keyset identifier="4" />
</package>
...
<shared-user name="com.android.emergency.uid" userId="10011">
<sigs count="1">
<cert index="1" />
</sigs>
<perms>
<item name="android.permission.MANAGE_USERS" granted="true" flags="0" />
</perms>
</shared-user>
<keyset-settings version="1">
<keys>
<public-key identifier="1" value="MIIBIDAN..." />
<public-key identifier="2" value="MIIBI..." />
<public-key identifier="3" value="MIIBI..." />
<public-key identifier="4" value="MIIBID..." />
</keys>
<keysets>
<keyset identifier="1">
<key-id identifier="1" />
</keyset>
<keyset identifier="2">
<key-id identifier="2" />
</keyset>
<keyset identifier="3">
<key-id identifier="3" />
</keyset>
<keyset identifier="4">
<key-id identifier="4" />
</keyset>
</keysets>
<lastIssuedKeyId value="4" />
<lastIssuedKeySetId value="4" />
</keyset-settings>
</packages>
可以看到，packages.xml主要记录了以下几方面的信息：
- 权限信息，permission-trees标签和permissions标签。这里记录的是系统里所有的权限条目
- 安装的App信息，包括系统App和用户自行安装的App，package和updated-package标签。其中package标签用户记录一般App的信息；而updated-package通常用于被用户手动升级了的系统App，比如说手机自带了计算器App，这个自带的App的版本是1.0，而厂商又在它的应用商店发布了计算器2.0，当我们在应用商店更新成2.0版本的时候，在系统分区和用户安装分区会各存在一个计算器App。这也是为什么我们在系统应用管理界面删除更新后的计算器2.0后，手机上还是会有计算器1.0版本，而不是彻底消失的原因。
package标签的属性记录了包名、代码路径、版本等各项信息。另外，package还会有一些子标签，sigs记录App的签名信息，perms记录App的权限信息，注意这里的权限是manifest中声明的权限而不是已经授予的权限。 - 共享用户信息，shared-user标签。一般来说一个Android系统会为每一个App分配一个user id，但是我们也可以在manifest元素中指定android:sharedUserId属性，使多个App具有同样的user id从而可以共享数据等等。但是除了系统App，Android强烈建议我们不要使用它，并且在未来的版本可能会被移除，所以了解即可。
- 签名信息，keyset-settings标签，记录的是应用签名的公钥。
packages.xml也不止以上这些标签，具体可以参考Settings类对packages.xml的解析：
boolean readLPw(@NonNull List<UserInfo> users) {
FileInputStream str = null;
if (mBackupSettingsFilename.exists()) {
try {
str = new FileInputStream(mBackupSettingsFilename);
mReadMessages.append("Reading from backup settings file\n");
PackageManagerService.reportSettingsProblem(Log.INFO,
"Need to read from backup settings file");
if (mSettingsFilename.exists()) {
Slog.w(PackageManagerService.TAG, "Cleaning up settings file "
+ mSettingsFilename);
mSettingsFilename.delete();
}
} catch (java.io.IOException e) {
}
}
mPendingPackages.clear();
mPastSignatures.clear();
mKeySetRefs.clear();
mInstallerPackages.clear();
try {
if (str == null) {
if (!mSettingsFilename.exists()) {
mReadMessages.append("No settings file found\n");
PackageManagerService.reportSettingsProblem(Log.INFO,
"No settings file; creating initial state");
findOrCreateVersion(StorageManager.UUID_PRIVATE_INTERNAL).forceCurrent();
findOrCreateVersion(StorageManager.UUID_PRIMARY_PHYSICAL).forceCurrent();
return false;
}
str = new FileInputStream(mSettingsFilename);
}
XmlPullParser parser = Xml.newPullParser();
parser.setInput(str, StandardCharsets.UTF_8.name());
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG
&& type != XmlPullParser.END_DOCUMENT) {
;
}
if (type != XmlPullParser.START_TAG) {
mReadMessages.append("No start tag found in settings file\n");
PackageManagerService.reportSettingsProblem(Log.WARN,
"No start tag found in package manager settings");
Slog.wtf(PackageManagerService.TAG,
"No start tag found in package manager settings");
return false;
}
int outerDepth = parser.getDepth();
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("package")) {
readPackageLPw(parser);
} else if (tagName.equals("permissions")) {
mPermissions.readPermissions(parser);
} else if (tagName.equals("permission-trees")) {
mPermissions.readPermissionTrees(parser);
} else if (tagName.equals("shared-user")) {
readSharedUserLPw(parser);
} else if (tagName.equals("preferred-packages")) {
} else if (tagName.equals("preferred-activities")) {
readPreferredActivitiesLPw(parser, 0);
} else if (tagName.equals(TAG_PERSISTENT_PREFERRED_ACTIVITIES)) {
readPersistentPreferredActivitiesLPw(parser, 0);
} else if (tagName.equals(TAG_CROSS_PROFILE_INTENT_FILTERS)) {
readCrossProfileIntentFiltersLPw(parser, 0);
} else if (tagName.equals(TAG_DEFAULT_BROWSER)) {
readDefaultAppsLPw(parser, 0);
} else if (tagName.equals("updated-package")) {
readDisabledSysPackageLPw(parser);
} else if (tagName.equals("renamed-package")) {
String nname = parser.getAttributeValue(null, "new");
String oname = parser.getAttributeValue(null, "old");
if (nname != null && oname != null) {
mRenamedPackages.put(nname, oname);
}
} else if (tagName.equals("restored-ivi")) {
readRestoredIntentFilterVerifications(parser);
} else if (tagName.equals("last-platform-version")) {
final VersionInfo internal = findOrCreateVersion(
StorageManager.UUID_PRIVATE_INTERNAL);
final VersionInfo external = findOrCreateVersion(
StorageManager.UUID_PRIMARY_PHYSICAL);
internal.sdkVersion = XmlUtils.readIntAttribute(parser, "internal", 0);
external.sdkVersion = XmlUtils.readIntAttribute(parser, "external", 0);
internal.fingerprint = external.fingerprint =
XmlUtils.readStringAttribute(parser, "fingerprint");
} else if (tagName.equals("database-version")) {
final VersionInfo internal = findOrCreateVersion(
StorageManager.UUID_PRIVATE_INTERNAL);
final VersionInfo external = findOrCreateVersion(
StorageManager.UUID_PRIMARY_PHYSICAL);
internal.databaseVersion = XmlUtils.readIntAttribute(parser, "internal", 0);
external.databaseVersion = XmlUtils.readIntAttribute(parser, "external", 0);
} else if (tagName.equals("verifier")) {
final String deviceIdentity = parser.getAttributeValue(null, "device");
try {
mVerifierDeviceIdentity = VerifierDeviceIdentity.parse(deviceIdentity);
} catch (IllegalArgumentException e) {
Slog.w(PackageManagerService.TAG, "Discard invalid verifier device id: "
+ e.getMessage());
}
} else if (TAG_READ_EXTERNAL_STORAGE.equals(tagName)) {
final String enforcement = parser.getAttributeValue(null, ATTR_ENFORCEMENT);
mReadExternalStorageEnforced =
"1".equals(enforcement) ? Boolean.TRUE : Boolean.FALSE;
} else if (tagName.equals("keyset-settings")) {
mKeySetManagerService.readKeySetsLPw(parser, mKeySetRefs);
} else if (TAG_VERSION.equals(tagName)) {
final String volumeUuid = XmlUtils.readStringAttribute(parser,
ATTR_VOLUME_UUID);
final VersionInfo ver = findOrCreateVersion(volumeUuid);
ver.sdkVersion = XmlUtils.readIntAttribute(parser, ATTR_SDK_VERSION);
ver.databaseVersion = XmlUtils.readIntAttribute(parser, ATTR_DATABASE_VERSION);
ver.fingerprint = XmlUtils.readStringAttribute(parser, ATTR_FINGERPRINT);
} else {
Slog.w(PackageManagerService.TAG, "Unknown element under <packages>: "
+ parser.getName());
XmlUtils.skipCurrentTag(parser);
}
}
str.close();
} catch (XmlPullParserException e) {
...
} catch (java.io.IOException e) {
...
}
...
return true;
}
3、Packages.xml的作用
在上篇文章中我们可以看到，packages.xml文件最终被解析和保存到了Settings的mPackages属性里了。来看一下PMS的构造方法里，它都发挥了什么作用吧
public PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {
...
mSettings = injector.getSettings();
...
t.traceBegin("addSharedUsers");
mSettings.addSharedUserLPw("android.uid.system", Process.SYSTEM_UID,
ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
mSettings.addSharedUserLPw("android.uid.phone", RADIO_UID,
ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
...
synchronized (mInstallLock) {
synchronized (mLock) {
...
t.traceBegin("read user settings");
mFirstBoot = !mSettings.readLPw(mInjector.getUserManagerInternal().getUsers(false));
t.traceEnd();
final int packageSettingCount = mSettings.mPackages.size();
for (int i = packageSettingCount - 1; i >= 0; i--) {
PackageSetting ps = mSettings.mPackages.valueAt(i);
if (!isExternal(ps) && (ps.codePath == null || !ps.codePath.exists())
&& mSettings.getDisabledSystemPkgLPr(ps.name) != null) {
mSettings.mPackages.removeAt(i);
mSettings.enableSystemPackageLPw(ps.name);
}
}
if (!mOnlyCore && mFirstBoot) {
requestCopyPreoptedFiles();
}
...
if (isDeviceUpgrading()) {
mExistingPackages = new ArraySet<>(mSettings.mPackages.size());
for (PackageSetting ps : mSettings.mPackages.values()) {
mExistingPackages.add(ps.name);
}
}
...
final List<String> possiblyDeletedUpdatedSystemApps = new ArrayList<>();
final List<String> stubSystemApps = new ArrayList<>();
if (!mOnlyCore) {
...
final Iterator<PackageSetting> psit = mSettings.mPackages.values().iterator();
while (psit.hasNext()) {
PackageSetting ps = psit.next();
if ((ps.pkgFlags & ApplicationInfo.FLAG_SYSTEM) == 0) {
continue;
}
final AndroidPackage scannedPkg = mPackages.get(ps.name);
if (scannedPkg != null) {
if (mSettings.isDisabledSystemPackageLPr(ps.name)) {
logCriticalInfo(Log.WARN,
"Expecting better updated system app for " + ps.name
+ "; removing system app. Last known"
+ " codePath=" + ps.codePathString
+ ", versionCode=" + ps.versionCode
+ "; scanned versionCode=" + scannedPkg.getLongVersionCode());
removePackageLI(scannedPkg, true);
mExpectingBetter.put(ps.name, ps.codePath);
}
continue;
}
if (!mSettings.isDisabledSystemPackageLPr(ps.name)) {
psit.remove();
logCriticalInfo(Log.WARN, "System package " + ps.name
+ " no longer exists; it's data will be wiped");
mPermissionManager.updatePermissions(ps.name, null);
} else {
final PackageSetting disabledPs =
mSettings.getDisabledSystemPkgLPr(ps.name);
if (disabledPs.codePath == null || !disabledPs.codePath.exists()
|| disabledPs.pkg == null) {
possiblyDeletedUpdatedSystemApps.add(ps.name);
} else {
mExpectingBetter.put(disabledPs.name, disabledPs.codePath);
}
}
}
}
final int cachedSystemApps = PackageCacher.sCachedPackageReadCount.get();
mSettings.pruneSharedUsersLPw();
...
if (!mOnlyCore) {
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,
SystemClock.uptimeMillis());
scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0,
packageParser, executorService);
}
packageParser.close();
List<Runnable> unfinishedTasks = executorService.shutdownNow();
if (!unfinishedTasks.isEmpty()) {
throw new IllegalStateException("Not all tasks finished before calling close: "
+ unfinishedTasks);
}
if (!mOnlyCore) {
for (int i = possiblyDeletedUpdatedSystemApps.size() - 1; i >= 0; --i) {
final String packageName = possiblyDeletedUpdatedSystemApps.get(i);
final AndroidPackage pkg = mPackages.get(packageName);
final String msg;
mSettings.removeDisabledSystemPackageLPw(packageName);
if (pkg == null) {
msg = "Updated system package " + packageName
+ " no longer exists; removing its data";
} else {
msg = "Updated system package " + packageName
+ " no longer exists; rescanning package on data";
removePackageLI(pkg, true);
try {
final File codePath = new File(pkg.getCodePath());
scanPackageTracedLI(codePath, 0, scanFlags, 0, null);
} catch (PackageManagerException e) {
Slog.e(TAG, "Failed to parse updated, ex-system package: "
+ e.getMessage());
}
}
final PackageSetting ps = mSettings.mPackages.get(packageName);
if (ps != null && mPackages.get(packageName) == null) {
removePackageDataLIF(ps, null, null, 0, false);
}
logCriticalInfo(Log.WARN, msg);
}
for (int i = 0; i < mExpectingBetter.size(); i++) {
final String packageName = mExpectingBetter.keyAt(i);
if (!mPackages.containsKey(packageName)) {
final File scanFile = mExpectingBetter.valueAt(i);
logCriticalInfo(Log.WARN, "Expected better " + packageName
+ " but never showed up; reverting to system");
@ParseFlags int reparseFlags = 0;
@ScanFlags int rescanFlags = 0;
for (int i1 = mDirsToScanAsSystem.size() - 1; i1 >= 0; i1--) {
final ScanPartition partition = mDirsToScanAsSystem.get(i1);
if (partition.containsPrivApp(scanFile)) {
reparseFlags = systemParseFlags;
rescanFlags = systemScanFlags | SCAN_AS_PRIVILEGED
| partition.scanFlag;
break;
}
if (partition.containsApp(scanFile)) {
reparseFlags = systemParseFlags;
rescanFlags = systemScanFlags | partition.scanFlag;
break;
}
}
if (rescanFlags == 0) {
Slog.e(TAG, "Ignoring unexpected fallback path " + scanFile);
continue;
}
mSettings.enableSystemPackageLPw(packageName);
try {
scanPackageTracedLI(scanFile, reparseFlags, rescanFlags, 0, null);
} catch (PackageManagerException e) {
Slog.e(TAG, "Failed to parse original system package: "
+ e.getMessage());
}
}
}
...
}
mExpectingBetter.clear();
...
for (SharedUserSetting setting : mSettings.getAllSharedUsersLPw()) {
final List<String> changedAbiCodePath =
applyAdjustedAbiToSharedUser(setting, null ,
mInjector.getAbiHelper().getAdjustedAbiForSharedUser(
setting.packages, null ));
if (changedAbiCodePath != null && changedAbiCodePath.size() > 0) {
for (int i = changedAbiCodePath.size() - 1; i >= 0; --i) {
final String codePathString = changedAbiCodePath.get(i);
try {
mInstaller.rmdex(codePathString,
getDexCodeInstructionSet(getPreferredInstructionSet()));
} catch (InstallerException ignored) {
}
}
}
setting.fixSeInfoLocked();
setting.updateProcesses();
}
mPackageUsage.read(mSettings.mPackages);
...
t.traceBegin("write settings");
mSettings.writeLPr();
...
mSettings.setPermissionControllerVersion(
getPackageInfo(mRequiredPermissionControllerPackage, 0,
UserHandle.USER_SYSTEM).getLongVersionCode());
...
}
}
...
}
这里删除了非常多的代码，只列出了关键性的。可以看到packages.xml的主要作用存储上一次启动时扫描和更新的结果，和本次启动扫描的结果进行比较，判断哪些该更新，哪些该删除。这就是它的主要作用。
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