本文基于Android_9.0、kernel_3.18源码
简介
servermanager提供了服务注册、服务获取等功能，以AMS（ActivityManagerService）为例：
首先，AMS通过binder将自己注册到servermanager中；
然后，其他进程通过binder从servermanager获取到AMS服务（取到的其实是代理）；
最后，通过获取到的AMS代理对象便能调用到AMS的方法。
本文主要介绍服务注册的流程。
调用SystemServer.java->main()流程
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
1、上文回顾
由上文Binder（四）system_server中binder的初始化我们已经知道，手机启动后，会通过ZygoteInit.forkSystemServer()来启动system_server进程。
private static Runnable forkSystemServer(String abiList, String socketName,
ZygoteServer zygoteServer) {
........
// 启动system_server的参数
String args[] = {
"--setuid=1000",
"--setgid=1000",
"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1024,1032,1065,3001,3002,3003,3006,3007,3009,3010",
"--capabilities=" + capabilities + "," + capabilities,
"--nice-name=system_server",
"--runtime-args",
"--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
"com.android.server.SystemServer",
};
ZygoteConnection.Arguments parsedArgs = null;
int pid;
try {
parsedArgs = new ZygoteConnection.Arguments(args);
// 创建进程
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.runtimeFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
}
if (pid == 0) {
// 进程其他操作
return handleSystemServerProcess(parsedArgs);
}
return null;
}
在创建完进程后，会通过handleSystemServerProcess()调用到ZygoteInit.zygoteInit()方法，在该方法中执行ZygoteInit.nativeZygoteInit()初始化Binder。
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
if (RuntimeInit.DEBUG) {
Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams();
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit();
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
在ZygoteInit.nativeZygoteInit()中，还做了另一个操作，RuntimeInit.applicationInit()，它的作用就是找到要启动的类，并调用它的main()方法。
2、RuntimeInit.applicationInit()分析
protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
........
final Arguments args = new Arguments(argv);
........
// Remaining arguments are passed to the start class's static main
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
static class Arguments {
String startClass;
String[] startArgs;
Arguments(String args[]) throws IllegalArgumentException {
parseArgs(args);
}
// 解析参数，获取到startClass，
private void parseArgs(String args[])
throws IllegalArgumentException {
int curArg = 0;
for (; curArg < args.length; curArg++) {
String arg = args[curArg];
if (arg.equals("--")) {
curArg++;
break;
} else if (!arg.startsWith("--")) {
break;
}
}
if (curArg == args.length) {
throw new IllegalArgumentException("Missing classname argument to RuntimeInit!");
}
startClass = args[curArg++];
startArgs = new String[args.length - curArg];
System.arraycopy(args, curArg, startArgs, 0, startArgs.length);
}
}
RuntimeInit.applicationInit()方法简单：
首先，通过new Arguments(argv)解析传过来的参数：设置args.startClass，即在ZygoteInit.forkSystemServer()中创建的参数"com.android.server.SystemServer"；
然后，通过findStaticMain()方法调用main方法。
// Invokes a static "main(argv[]) method on class "className".
protected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
// 加载class
Class<?> cl;
try {
cl = Class.forName(className, true, classLoader);
} catch () {}
........
// 获取main方法
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
}catch () {}
........
// 方法校验
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
return new MethodAndArgsCaller(m, argv);
}
在findStaticMain()方法中：
首先，通过Class.forName()的方式获取到Class对象；
然后，通过反射获取到main()方法；
最后，直接生成MethodAndArgsCaller对象，return回去。
static class MethodAndArgsCaller implements Runnable {
private final Method mMethod;
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod = method;
mArgs = args;
}
public void run() {
try {
mMethod.invoke(null, new Object[] { mArgs });
} catch () {}
}
}
public static void main(String argv[]) {
........
if (startSystemServer) {
Runrunnable r = forkSystemServer(abiList, socketName, zygoteServer);
if (r != null) {
r.run();
return;
}
}
........
}
MethodAndArgsCaller继承自Runnable接口，实现了run()方法，在run()方法中，直接通过method.invoke()调用方法。回顾ZygoteInit.java->main()的内容，通过forkSystemServer()获取到Runrunnable对象之后，直接执行了它的run()方法。
至此，我们便知道从App启动->Zyogte进程启动->system_server进程启动->SystemServer的main方法的过程。下面我们详细分析SystemServer做了哪些事情。
服务注册流程
frameworks/base/services/java/com/android/server/SystemServer.java
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
frameworks/base/services/core/java/com/android/server/SystemServiceManager.java
frameworks/base/core/java/android/os/ServiceManager.java
frameworks/base/core/java/com/android/internal/os/BinderInternal.java
frameworks/base/core/jni/android_util_Binder.cpp
frameworks/native/libs/binder/ProcessState.cpp
frameworks/native/include/binder/ProcessState.h
frameworks/native/libs/binder/BpBinder.cpp
frameworks/native/libs/binder/IPCThreadState.cpp
frameworks/base/core/java/android/os/Binder.java
frameworks/base/core/java/android/os/ServiceManagerNative.java
SystemServer.main分析
public static void main(String[] args) {
new SystemServer().run();
}
private void run() {
...
try {
...
mSystemServiceManager = new SystemServiceManager(mSystemContext);
...
} finally {
traceEnd(); // InitBeforeStartServices
}
...
// Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
...
}
在main方法中，创建了SystemServer对象，然后执行了它的run()方法。在run方法中，启动了各种各样的services，如：AMS、PMS、WMS等。接下来以AMS为例进行分析。
startBootstrapServices()
private void startBootstrapServices() {
...
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
...
mActivityManagerService.setSystemProcess();
...
}
在startBootstrapServices中，通过mSystemServiceManager.startService().getService()生成AMS，然后调用mActivityManagerService.setSystemProcess()进行注册。
AMS的创建
public <T extends SystemService> T startService(Class<T> serviceClass) {
try {
// Create the service.
...
final T service;
try {
Constructor<T> constructor = serviceClass.getConstructor(Context.class);
service = constructor.newInstance(mContext);
} catch () {}
startService(service);
return service;
}
}
查看SystemServiceManager的startService方法，方法中通过反射得到传入的类的对象,即ActivityManagerService$Lifecycle，然后返回。也就是上文中的getService()会调用到ActivityManagerService$Lifecycle的getService()。
public static final class Lifecycle extends SystemService {
private final ActivityManagerService mService;
public Lifecycle(Context context) {
super(context);
mService = new ActivityManagerService(context);
}
@Override
public void onStart() {
mService.start();
}
@Override
public void onBootPhase(int phase) {
mService.mBootPhase = phase;
if (phase == PHASE_SYSTEM_SERVICES_READY) {
mService.mBatteryStatsService.systemServicesReady();
mService.mServices.systemServicesReady();
}
}
@Override
public void onCleanupUser(int userId) {
mService.mBatteryStatsService.onCleanupUser(userId);
}
public ActivityManagerService getService() {
return mService;
}
}
可以看到，ActivityManagerService$Lifecycle就是对AMS的一个包装，在构造方法中，会生成AMS，然后通过geService()返回。
AMS注册
1、IServiceManager实例的创建
public void setSystemProcess() {
try {
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
......
} catch () {}
}
查看setSystemProcess，它通过调用ServiceManager.addService()进行注册。
/**
* Place a new @a service called @a name into the service
* manager.
*
* @param name the name of the new service
* @param service the service object
* @param allowIsolated set to true to allow isolated sandboxed processes
* @param dumpPriority supported dump priority levels as a bitmask
* to access this service
*/
public static void addService(String name, IBinder service, boolean allowIsolated,
int dumpPriority) {
try {
getIServiceManager().addService(name, service, allowIsolated, dumpPriority);
} catch (RemoteException e) {
Log.e(TAG, "error in addService", e);
}
}
addService通过getIserviceManager()获取IServiceManager实例，然后调用addService进行注册。
private static IServiceManager getIServiceManager() {
if (sServiceManager != null) {
return sServiceManager;
}
// Find the service manager
sServiceManager = ServiceManagerNative
.asInterface(Binder.allowBlocking(BinderInternal.getContextObject()));
return sServiceManager;
}
getIServiceManager中生成了IServiceManager实例，它包含三个步骤：
1、BinderInternal.getContextObject()
2、Binder.allowBlocking()
3、ServiceManagerNative.asInterface()
下面逐一进行解析：
1.1、BinderInternal.getContextObject()
BinderInternal.getContextObject()调用的是Native方法，该方法在android_util_Binder.cpp中。
static jobject android_os_BinderInternal_getContextObject(JNIEnv* env, jobject clazz)
{
sp<IBinder> b = ProcessState::self()->getContextObject(NULL);
return javaObjectForIBinder(env, b);
}
此方法会调用ProcessState的getContextObject()，在ProcessState::getContextObject()中，会通过getStrongProxyForHandle(0)返回sp<IBinder>对象，此处的0代表servermanager的句柄。
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
return getStrongProxyForHandle(0);
}
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{
sp<IBinder> result;
AutoMutex _l(mLock);
// 找到句柄为handle的handle_entry对象，如果找不到，则新建handle对应的handle_entry
handle_entry* e = lookupHandleLocked(handle);
if (e != NULL) {
// 如果通过handle_entry找不到BpBinder，则创建一个
IBinder* b = e->binder;
if (b == NULL || !e->refs->attemptIncWeak(this)) {
if (handle == 0) {
Parcel data;
// 执行一个假任务检测context manager是否注册成功
status_t status = IPCThreadState::self()->transact(
0, IBinder::PING_TRANSACTION, data, NULL, 0);
if (status == DEAD_OBJECT)
return NULL;
}
// 创建BpBinder
b = BpBinder::create(handle);
e->binder = b;
if (b) e->refs = b->getWeakRefs();
result = b;
} else {
// This little bit of nastyness is to allow us to add a primary
// reference to the remote proxy when this team doesn't have one
// but another team is sending the handle to us.
result.force_set(b);
e->refs->decWeak(this);
}
}
return result;
}
getStrongProxyForHandle()的目的是返回句柄为handle的IBinder代理，这里是返回Service Manager的IBinder代理。
首先，通过lookupHandleLocked()得到handle_entry对象；
然后，如果handle == 0，则通过发送虚拟事务检测context manager是否注册成功；
最后，通过BpBinder::create(handle)创建BpBinder，并存入handle_entry中。
1.1.1、ProcessState::lookupHandleLocked()
Vector<handle_entry>mHandleToObject;
ProcessState::handle_entry* ProcessState::lookupHandleLocked(int32_t handle)
{
const size_t N=mHandleToObject.size();
if (N <= (size_t)handle) {
handle_entry e;
e.binder = NULL;
e.refs = NULL;
status_t err = mHandleToObject.insertAt(e, N, handle+1-N);
if (err < NO_ERROR) return NULL;
}
return &mHandleToObject.editItemAt(handle);
}
如果没有handle_entry，则创建新的handle_entry并将其插入到mHandleToObject中。mHandleToObject定义在ProcessState.h中，是一个Vector。
1.1.2、BpBinder::create(handle)
BpBinder* BpBinder::create(int32_t handle) {
int32_t trackedUid = -1;
...
return new BpBinder(handle, trackedUid);
}
BpBinder::BpBinder(int32_t handle, int32_t trackedUid)
: mHandle(handle)
, mAlive(1)
, mObitsSent(0)
, mObituaries(NULL)
, mTrackedUid(trackedUid)
{
ALOGV("Creating BpBinder %p handle %d\n", this, mHandle);
extendObjectLifetime(OBJECT_LIFETIME_WEAK);
IPCThreadState::self()->incWeakHandle(handle, this);
}
在BpBinder::create(handle)中，通过new BpBinder(handle, trackedUid)生成BpBinder对象。在BpBinder的构造函数中，调用了IPCThreadState::incWeakHandle方法。
1.1.3、IPCThreadState::incWeakHandle()
通过上一篇文章我们已经知道，IPCThreadState在初始化进程时已经创建，并且初始化了mOut、mIn。
void IPCThreadState::incWeakHandle(int32_t handle, BpBinder *proxy)
{
LOG_REMOTEREFS("IPCThreadState::incWeakHandle(%d)\n", handle);
// 增加binder引用的指令，还存在mOut中
mOut.writeInt32(BC_INCREFS);
mOut.writeInt32(handle);
// Create a temp reference until the driver has handled this command.
proxy->getWeakRefs()->incWeak(mProcess.get());
mPostWriteWeakDerefs.push(proxy->getWeakRefs());
}
通过incWeakHandle增加引用计数，同时在mOut中缓存BC_INCREFS指令，等待下一次调用ioctl与binder驱动通信时，告诉驱动增加相应的binder_ref的弱引用计数。
引用计数与智能指针有关，想了解的小伙伴可以自行搜索。
1.1.4、javaObjectForIBinder()
通过上面的流程，我们得到了sp<IBinder>即BpBinder对象，在传递个java之前，做了一次封装。
struct BinderProxyNativeData {
sp<IBinder> mObject;
sp<DeathRecipientList> mOrgue;
};
jobject javaObjectForIBinder(JNIEnv* env, const sp<IBinder>& val)
{
...
// 生成包装类BinderProxyNativeData
BinderProxyNativeData* nativeData = gNativeDataCache;
if (nativeData == nullptr) {
nativeData = new BinderProxyNativeData();
}
...
// 调用java方法生成java对象
jobject object = env->CallStaticObjectMethod(gBinderProxyOffsets.mClass,
gBinderProxyOffsets.mGetInstance, (jlong) nativeData, (jlong) val.get());
...
BinderProxyNativeData* actualNativeData = getBPNativeData(env, object);
if (actualNativeData == nativeData) {
// New BinderProxy; we still have exclusive access.
nativeData->mOrgue = new DeathRecipientList;
// 将BpBinder赋值给nativeData
nativeData->mObject = val;
gNativeDataCache = nullptr;
++gNumProxies;
if (gNumProxies >= gProxiesWarned + PROXY_WARN_INTERVAL) {
ALOGW("Unexpectedly many live BinderProxies: %d\n", gNumProxies);
gProxiesWarned = gNumProxies;
}
} else {
// nativeData wasn't used. Reuse it the next time.
gNativeDataCache = nativeData;
}
return object;
}
首先，得到包装类BinderProxyNativeData；
然后，通过CallStaticObjectMethod()生成java对象；
最后，如果BinderProxyNativeData是新生成的，将BpBinder赋值给它。
我们观察到有一个gBinderProxyOffsets参数，去看看它在哪里初始化的：
const char* const kBinderProxyPathName = "android/os/BinderProxy";
// 加载android/os/BinderProxy
static int int_register_android_os_BinderProxy(JNIEnv* env){
...
clazz = FindClassOrDie(env, kBinderProxyPathName);
gBinderProxyOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
gBinderProxyOffsets.mGetInstance = GetStaticMethodIDOrDie(env, clazz, "getInstance",
"(JJ)Landroid/os/BinderProxy;");
...
}
int register_android_os_Binder(JNIEnv* env){
...
if (int_register_android_os_BinderProxy(env) < 0)
return -1;
...
}
可知，在int_register_android_os_BinderProxy方法中会解析gBinderProxyOffsets的参数，mClass是android/os/BinderProxy，mGetInstance 是getInstance方法。
而int_register_android_os_BinderProxy是在register_android_os_Binder调用的。我们还记得native会通过AndroidRuntime::start()启动虚拟机，并拉起ZygoteInit。其实在start里还进行了android方法的注册。
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote){
// 注册android方法
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
}
// 注册android静态方法
int AndroidRuntime::startReg(JNIEnv* env){
...
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
env->PopLocalFrame(NULL);
return -1;
}
...
}
// 直接调用mProc
static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env){
for (size_t i = 0; i < count; i++) {
if (array[i].mProc(env) < 0) {
return -1;
}
}
return 0;
}
AndroidRuntime::start()通过startReg()注册android方法，gRegJNI是一个RegJNIRec数组，数组中添加了register_android_os_Binder。下面是它的定义：
#define REG_JNI(name) { name }
struct RegJNIRec {
int (*mProc)(JNIEnv*);
};
static const RegJNIRec gRegJNI[] = {
...
REG_JNI(register_android_os_Binder),
...
}
根据上文，我们知道在javaObjectForIBinder中，通过CallStaticObjectMethod会调用到java层BinderProxy.getInstance()方法。
传递的参数分别是nativeData和BpBinder。
BinderProxy
final class BinderProxy implements IBinder {
// BinderProxyNativeData引用
private final long mNativeData;
private BinderProxy(long nativeData) {
mNativeData = nativeData;
}
private static BinderProxy getInstance(long nativeData, long iBinder) {
BinderProxy result;
try {
// 从缓存中查
result = sProxyMap.get(iBinder);
if (result != null) {
return result;
}
// 查不到生成新的BinderProxy
result = new BinderProxy(nativeData);
} catch (Throwable e) {}
...
// 添加缓存
sProxyMap.set(iBinder, result);
return result;
}
}
BinderProxy.getInstance()会生成BinderProxy对象，并将其缓存在sProxyMap中。
至此，我们能够知道，通过BinderInternal.getContextObject()最终会获取到BinderProxy对象，它的持有关系如下：BinderProxy->BinderProxyNativeData->BpBinder->handle = 0，这样我们便能通过BinderProxy与servermanager通信了。
1.2、Binder.allowBlocking()
public static IBinder allowBlocking(IBinder binder) {
try {
if (binder instanceof BinderProxy) {
((BinderProxy) binder).mWarnOnBlocking = false;
} else if (binder != null && binder.getInterfaceDescriptor() != null
&& binder.queryLocalInterface(binder.getInterfaceDescriptor()) == null) {
Log.w(TAG, "Unable to allow blocking on interface " + binder);
}
} catch (RemoteException ignored) {
}
return binder;
}
设置binder的参数，对我们分析流程意义不大，可以看到它在设置完后，直接将binder返回，也就是我们上一个流程创建的BinderProxy。
1.3、ServiceManagerNative.asInterface()
static public IServiceManager asInterface(IBinder obj){
if (obj == null) {
return null;
}
IServiceManager in =
(IServiceManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ServiceManagerProxy(obj);
}
final class BinderProxy implements IBinder {
public IInterface queryLocalInterface(String descriptor) {
return null;
}
}
先通过queryLocalInterface查询，如果为null就生成一个ServiceManagerProxy，通过查看BinderProxy的queryLocalInterface可知，最终会返回ServiceManagerProxy对象。
class ServiceManagerProxy implements IServiceManager {
public ServiceManagerProxy(IBinder remote) {
mRemote = remote;
}
public IBinder asBinder() {
return mRemote;
}
}
ServiceManagerProxy主要是对BinderProxy的包装。
至此，ServiceManager.getIServiceManager流程分析完毕，最终会返回ServiceManagerProxy，它是对BinderProxy的包装，内部持有BinderProxy对象。
2、getIServiceManager().addService()注册
2.1、数据发送到binder驱动
public void addService(String name, IBinder service, boolean allowIsolated, int dumpPriority)
throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IServiceManager.descriptor);
data.writeString(name);
data.writeStrongBinder(service);
data.writeInt(allowIsolated ? 1 : 0);
data.writeInt(dumpPriority);
mRemote.transact(ADD_SERVICE_TRANSACTION, data, reply, 0);
reply.recycle();
data.recycle();
}
查看ServiceManagerProxy的addService方法，它通过Parcel对服务内容进行了封装，然后通过mRemote(BinderProxy)的transact进行发送。
public final void writeStrongBinder(IBinder val) {
nativeWriteStrongBinder(mNativePtr, val);
}
static const JNINativeMethod gParcelMethods[] = {
{"nativeWriteStrongBinder", "(JLandroid/os/IBinder;)V", (void*)android_os_Parcel_writeStrongBinder},
}
static void android_os_Parcel_writeStrongBinder(JNIEnv* env, jclass clazz, jlong nativePtr, jobject object)
{
Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
if (parcel != NULL) {
const status_t err = parcel->writeStrongBinder(ibinderForJavaObject(env, object));
if (err != NO_ERROR) {
signalExceptionForError(env, clazz, err);
}
}
}
writeStrongBinder方法会调用到native层的android_os_Parcel_writeStrongBinder中，在此方法中会调用到native层parcel的writeStrongBinder方法。
status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}
status_t flatten_binder(const sp<ProcessState>& /*proc*/,
const sp<IBinder>& binder, Parcel* out){
flat_binder_object obj;
...
obj.hdr.type = BINDER_TYPE_BINDER;
obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs());
...
return finish_flatten_binder(binder, obj, out);
}
flat_binder_object中的type为BINDER_TYPE_BINDER。接下来查看transact方法：
public boolean transact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
// 检查数据的大小
Binder.checkParcel(this, code, data, "Unreasonably large binder buffer");
...
try {
return transactNative(code, data, reply, flags);
} finally {}
}
// 数据检测，不能超过800k
static void checkParcel(IBinder obj, int code, Parcel parcel, String msg) {
if (CHECK_PARCEL_SIZE && parcel.dataSize() >= 800*1024) {
// Trying to send > 800k, this is way too much
StringBuilder sb = new StringBuilder();
...
Slog.wtfStack(TAG, sb.toString());
}
}
在BinderProxy的transact中，先调用Binder.checkParcel对数据大小进行检查，然后使用transactNative发送数据。
static const JNINativeMethod gBinderProxyMethods[] = {
{"transactNative", "(ILandroid/os/Parcel;Landroid/os/Parcel;I)Z", (void*)android_os_BinderProxy_transact},
};
static jboolean android_os_BinderProxy_transact(JNIEnv* env, jobject obj,
jint code, jobject dataObj, jobject replyObj, jint flags) // throws RemoteException{
...
// 得到发送的parcel
Parcel* data = parcelForJavaObject(env, dataObj);
...
// 得到回复的parcel
Parcel* reply = parcelForJavaObject(env, replyObj);
...
// 先得到BinderProxyNativeData，然后获取到BpBinder
IBinder* target = getBPNativeData(env, obj)->mObject.get();
...
// 调用BpBinder的transact
status_t err = target->transact(code, *data, reply, flags);
...
}
transactNative会调用到android_util_Binder的android_os_BinderProxy_transact方法，他首先通过java对象得到发送数据、接受返回的parcel对象，然后再得到BpBinder对象，调用BpBinder的transact进行数据发送。
status_t BpBinder::transact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
// Once a binder has died, it will never come back to life.
if (mAlive) {
status_t status = IPCThreadState::self()->transact(
mHandle, code, data, reply, flags);
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
}
在BpBinder中又通过IPCThreadState::self()->transact()进行数据传输。
status_t IPCThreadState::transact(int32_t handle,
uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags){
status_t err;
flags |= TF_ACCEPT_FDS;
...
// 数据打包：handle是BpBinder的mHandle = 0（servermanager）
// code = ADD_SERVICE_TRANSACTION，在getIServiceManager().addService()设置的code
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
if (err != NO_ERROR) {
if (reply) reply->setError(err);
return (mLastError = err);
}
if ((flags & TF_ONE_WAY) == 0) {
...
if (reply) {
...
// 数据发送给Binder驱动
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
} else {
err = waitForResponse(NULL, NULL);
}
return err;
}
IPCThreadState::self()->transact()中做了两步操作：
首先，通过writeTransactionData对数据进行打包，注意：这里的code = ADD_SERVICE_TRANSACTION，handle = 0；
然后，通过waitForResponse将数据发送给binder驱动。
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
binder_transaction_data tr;
tr.target.ptr = 0; /* Don't pass uninitialized stack data to a remote process */
tr.target.handle = handle;
tr.code = code;
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
const status_t err = data.errorCheck();
if (err == NO_ERROR) {
tr.data_size = data.ipcDataSize();
tr.data.ptr.buffer = data.ipcData();
tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t);
tr.data.ptr.offsets = data.ipcObjects();
} else if (statusBuffer) {} else {}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}
writeTransactionData会将数据打包到binder_transaction_data中，并将BC_TRANSACTION和binder_transaction_data加入到mOut中进行缓存。
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
uint32_t cmd;
int32_t err;
while (1) {
// 通过talkWithDriver与binder交互
if ((err=talkWithDriver()) < NO_ERROR) break;
...
// 读取返回结果
cmd = (uint32_t)mIn.readInt32();
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
...
case BR_DEAD_REPLY:
...
case BR_FAILED_REPLY:
...
case BR_ACQUIRE_RESULT:
...
case BR_REPLY:
...
default:
...
}
}
finish:
...
return err;
}
在waitForResponse中，通过talkWithDriver与binder交互，在根据返回值进行相应的处理。
status_t IPCThreadState::talkWithDriver(bool doReceive){
...
binder_write_read bwr;
const bool needRead = mIn.dataPosition() >= mIn.dataSize();
const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0;
bwr.write_size = outAvail;
bwr.write_buffer = (uintptr_t)mOut.data();
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();
bwr.read_buffer = (uintptr_t)mIn.data();
} else {
bwr.read_size = 0;
bwr.read_buffer = 0;
}
...
do {
...
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)
err = NO_ERROR;
else
err = -errno;
...
} while (err == -EINTR);
return err;
}
talkWithDriver在Binder（四）system_server中binder的初始化中已经分析过：它先将数据封装在binder_write_read 中，然后调用ioctl与binder进行通信。由于mIn中还没有写入数据，因此needRead=true，bwr中write_size和read_size都>0。
至此，经过重重包装，我们看一下现在的数据结构：
2.2、binder驱动收到数据后的处理
ioctl在Binder（三）servicemanager初始化中分析过：BINDER_WRITE_READ会走到binder_ioctl_write_read方法中，
static int binder_ioctl_write_read(struct file *filp,
unsigned int cmd, unsigned long arg,
struct binder_thread *thread){
...
// 如果write_size>0，则进行写操作
if (bwr.write_size > 0) {
ret = binder_thread_write(proc, thread,bwr.write_buffer,bwr.write_size,&bwr.write_consumed);
...
}
// 如果read_size>0，则进行读操作
if (bwr.read_size > 0) {
ret = binder_thread_read(proc, thread, bwr.read_buffer,bwr.read_size,&bwr.read_consumed,filp->f_flags & O_NONBLOCK);
...
}
...
}
在binder_ioctl_write_read中，会分别通过binder_thread_write读取发送过来的数据，通过binder_thread_read返回数据。
static int binder_thread_write(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed)
{
uint32_t cmd;
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
while (ptr < end && thread->return_error == BR_OK) {
if (get_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
...
switch (cmd) {
...
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd == BC_REPLY);
break;
}
...
}
return 0;
}
在binder_thread_write中，对于BC_TRANSACTION指令，会交由binder_transaction处理。
static void binder_transaction(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_transaction_data *tr, int reply){
struct binder_transaction *t;
struct binder_work *tcomplete;
binder_size_t *offp, *off_end;
binder_size_t off_min;
struct binder_proc *target_proc;
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list;
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
struct binder_transaction_log_entry *e;
uint32_t return_error;
...
if (reply) {
...
} else {
// handle = 0，为假
if (tr->target.handle) {
struct binder_ref *ref;
// 通过handle查找binder_ref
ref = binder_get_ref(proc, tr->target.handle);
if (ref == NULL) {
...
// 如果找不到说明没有注册
goto err_invalid_target_handle;
}
target_node = ref->node;
} else {
// 如果handle为0，表示找的是servermanager
target_node = binder_context_mgr_node;
...
}
e->to_node = target_node->debug_id;
// 设置处理事务的目标进程
target_proc = target_node->proc;
...
}
if (target_thread) {
...
} else {
target_list = &target_proc->todo;
target_wait = &target_proc->wait;
}
e->to_proc = target_proc->pid;
// 分配一个待处理事务binder_transaction
t = kzalloc(sizeof(*t), GFP_KERNEL);
...
// 分配一个待完成的工作binder_work
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
...
if (!reply && !(tr->flags & TF_ONE_WAY))
// 设置from，表示事务是从哪里发起的
t->from = thread;
else
t->from = NULL;
// 初始化事务
t->sender_euid = task_euid(proc->tsk);
t->to_proc = target_proc; // 设置目标进程
t->to_thread = target_thread; // 设置目标线程
t->code = tr->code;// 事务的code = ADD_SERVICE_TRANSACTION
t->flags = tr->flags;
t->priority = task_nice(current);
t->buffer = binder_alloc_buf(target_proc, tr->data_size,tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); // 分配空间
t->buffer->transaction = t; // 保存事务
t->buffer->target_node = target_node; // 保存事务的目标binder_node
...
// 拷贝数据
if (copy_from_user(t->buffer->data, (const void __user *)(uintptr_t)tr->data.ptr.buffer, tr->data_size)) {}
if (copy_from_user(offp, (const void __user *)(uintptr_t)tr->data.ptr.offsets, tr->offsets_size)) {}
...
for (; offp < off_end; offp++) {
struct flat_binder_object *fp;
...
fp = (struct flat_binder_object *)(t->buffer->data + *offp);
off_min = *offp + sizeof(struct flat_binder_object);
switch (fp->type) {
case BINDER_TYPE_BINDER:
case BINDER_TYPE_WEAK_BINDER: {
struct binder_ref *ref;
// 在proc中找到parcel中binder对应的binder_node，即AMS的binder_node
struct binder_node *node = binder_get_node(proc, fp->binder);
// 如果没有找到，新建一个
if (node == NULL) {
node = binder_new_node(proc, fp->binder, fp->cookie);
...
node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
}
...
// 在target_proc(servicemanager)中查找是否有该实体的引用
// 如果没有，则添加到target_proc->refs_by_node红黑树中，便于servicemanager管理
ref = binder_get_ref_for_node(target_proc, node);
if (ref == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_get_ref_for_node_failed;
}
// 修改type
if (fp->type == BINDER_TYPE_BINDER)
fp->type = BINDER_TYPE_HANDLE;
else
fp->type = BINDER_TYPE_WEAK_HANDLE;
// 设置handle的值，通过handle可以从servicemanager中找到对应的binder_ref，从而找到binder_node
fp->handle = ref->desc;
// 增加引用计数
binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE,
&thread->todo);
...
} break;
...
}
}
if (reply) {
...
} else if (!(t->flags & TF_ONE_WAY)) {
BUG_ON(t->buffer->async_transaction != 0);
t->need_reply = 1;
t->from_parent = thread->transaction_stack;
// 将事务添加到当前线程的事务栈中
thread->transaction_stack = t;
} else {
...
}
// 设置事务类型，并将其加入队列
t->work.type = BINDER_WORK_TRANSACTION;
list_add_tail(&t->work.entry, target_list);
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
// 将complete添加到thread->todo队列中
list_add_tail(&tcomplete->entry, &thread->todo);
// 唤醒目标进程
if (target_wait)
wake_up_interruptible(target_wait);
return;
...
}
首先，通过handle = 0，找到处理这次事务binder_node，即servicemanager，从而对目标数据进程赋值：target_node、target_proc、target_list、target_wait；
然后，新建事务binder_transaction，对事务数据进行初始化；
再然后，解析flat_binder_object数据，这里面封装这AMS的数据，查找/创建AMS对应的binder_node，再通过binder_get_ref_for_node查找/创建该binder_node对应的binder_ref；新建好binder_ref后，将其添加到servicemanager的红黑树中，这样servicemanager就能对AMS进行管理了；
最后，设置待处理事务的类型为BINDER_WORK_TRANSACTION，将其加入目标进程的todo队列；待完成工作的类型为BINDER_WORK_TRANSACTION_COMPLETE，将complete添加到thread->todo队列中，然后唤醒等待队列。
注意，此时都运行在AMS的进程中，通过唤醒等待队列操作会将servicemanager进程唤醒进行处理，先将AMS进程的流程分析完毕。
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed, int non_block){
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
int ret = 0;
int wait_for_proc_work;
// 如果*consumed=0，则写入BR_NOOP到用户传进来的bwr.read_buffer缓存区
if (*consumed == 0) {
if (put_user(BR_NOOP, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
}
...
retry:
// 当线程的事务栈为空 且 待处理事务列表为空时，该标记位true。
// binder_transaction中添加了待完成工作，因此hread->todo并不为空
wait_for_proc_work = thread->transaction_stack == NULL && list_empty(&thread->todo);
if (wait_for_proc_work) {
...
} else {
if (non_block) {
...
} else
// todo不为空，不需要等待
ret = wait_event_freezable(thread->wait, binder_has_thread_work(thread));
}
...
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
// 取出待完成工作
if (!list_empty(&thread->todo)) {
w = list_first_entry(&thread->todo, struct binder_work,
entry);
} else if () {} else {}
...
switch (w->type) {
case BINDER_WORK_TRANSACTION_COMPLETE: {
// 将BR_TRANSACTION_COMPLETE写入到用户缓冲空间中
cmd = BR_TRANSACTION_COMPLETE;
if (put_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
binder_stat_br(proc, thread, cmd);
list_del(&w->entry);
kfree(w);
binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
} break;
}
...
}
...
return 0;
}
首先，由于consumed=0，因此会先将BR_NOOP从内核空间拷贝到用户空间；
然后，由于binder_transaction中添加了待完成工作，因此hread->todo并不为空；因此会走到while循环，将BR_TRANSACTION_COMPLETE写入用户空间。
status_t IPCThreadState::talkWithDriver(bool doReceive){
...
do {
...
// 返回值 = 0
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)
err = NO_ERROR;
else
err = -errno;
...
} while (err == -EINTR);
...
if (err >= NO_ERROR) {
if (bwr.write_consumed > 0) {
if (bwr.write_consumed < mOut.dataSize())
mOut.remove(0, bwr.write_consumed);
else {
mOut.setDataSize(0);
processPostWriteDerefs();
}
}
if (bwr.read_consumed > 0) {
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition(0);
}
return NO_ERROR;
}
return err;
}
返回到talkWithDriver；ioclt返回值=0；因此err = NO_ERROR；然后返回到waitForResponse中。在waitForResponse会根据cmd进行相应的处理。
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult){
uint32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
...
cmd = (uint32_t)mIn.readInt32();
...
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;
break;
case BR_DEAD_REPLY:
...
case BR_FAILED_REPLY:
...
case BR_ACQUIRE_RESULT:
...
case BR_REPLY:
...
default:
err = executeCommand(cmd);
if (err != NO_ERROR) goto finish;
break;
}
}
...
return err;
}
status_t IPCThreadState::executeCommand(int32_t cmd){
BBinder* obj;
RefBase::weakref_type* refs;
status_t result = NO_ERROR;
switch ((uint32_t)cmd) {
...
case BR_NOOP:
break;
}
...
return result;
}
首先，读取到cmd = BR_NOOP，然后再default中由executeCommand处理，在executeCommand中什么都没做；
然后，通过循环，再次进入talkWithDriver，由于数据未读完，会通过if ((bwr.write_size == 0) && (bwr.read_size == 0)) return NO_ERROR返回；
最后，读取cmd = BR_TRANSACTION_COMPLETE，由于reply ！= 0，因此会再次循环进入talkWithDriver。
再次进入talkWithDriver中，write_size = 0，read_size != 0（needRead = true），因此会触发ioctl中的binder_thread_read，在当前线程中的事务栈和待处理事务都是空，会执行wait_event_interruptible_exclusive进行阻塞，等待servicemanager的反馈信息。
