本文转载自:https://blog.csdn.net/yangwen123/article/details/79854267
通过前面对Treble架构的介绍，我们知道，Android Framework进程和Hal分离，每个Hal独立运行在自己的进程地址空间，那么这些Hal进程是如何启动的呢？本文以composer hal为例展开分析。
在以下路径有composer hal的rc启动脚本：
hardware/interfaces/graphics/composer/2.1/default/android.hardware.graphics.composer@2.1-service.rc
service hwcomposer-2-1 /vendor/bin/hw/android.hardware.graphics.composer@2.1-service
class hal animation
user system
group graphics drmrpc
capabilities SYS_NICE
onrestart restart surfaceflinger
编译后，会将该脚本文件copy到vendor/etc/init目录，在开机时，init进程会读取并解析这个脚本，然后启动android.hardware.graphics.composer@2.1-service进程：
system 661 1 32288 7832 0 0 S android.hardware.graphics.composer@2.1-service
该进程的可执行文件是：vendor/bin/hw/android.hardware.graphics.composer@2.1-service，
该可执行文件对应的源码为：hardware/interfaces/graphics/composer/2.1/default/service.cpp
composer Hal启动过程
hardware/interfaces/graphics/composer/2.1/default/service.cpp
int main() {
// the conventional HAL might start binder services
android::ProcessState::initWithDriver("/dev/vndbinder");
android::ProcessState::self()->setThreadPoolMaxThreadCount(4);
android::ProcessState::self()->startThreadPool();
// same as SF main thread
struct sched_param param = {0};
param.sched_priority = 2;
if (sched_setscheduler(0, SCHED_FIFO | SCHED_RESET_ON_FORK,
¶m) != 0) {
ALOGE("Couldn't set SCHED_FIFO: %d", errno);
}
return defaultPassthroughServiceImplementation<IComposer>(4);
}
前面我们分析了Treble架构下的binder通信变化，在Treble架构下，存在了3个binder设备，分别是/dev/binder、/dev/vndbinder、/dev/hwbinder，上层需要通过binder库来访问这些binder设备，而/dev/binder和/dev/vndbinder都是由libbinder来访问，因此需要指定打开的binder设备。
android::ProcessState::initWithDriver("/dev/vndbinder");
这句说明composer hal通过vndbinder来通信的，接下来就是设置binder线程个数为4，并启动binder线程池，然后调用
defaultPassthroughServiceImplementation<IComposer>(4)
完成composer hal的启动。
systemlibhidl ransportincludehidlLegacySupport.h
template<class Interface>
__attribute__((warn_unused_result))
status_t defaultPassthroughServiceImplementation(std::string name,
size_t maxThreads = 1) {
configureRpcThreadpool(maxThreads, true); //配置binder线程个数
status_t result = registerPassthroughServiceImplementation<Interface>(name);
if (result != OK) {
return result;
}
joinRpcThreadpool();
return 0;
}
template<class Interface>
__attribute__((warn_unused_result))
status_t registerPassthroughServiceImplementation(
std::string name = "default") {
sp<Interface> service = Interface::getService(name, true /* getStub */); //从当前进程空间中拿到IComposer接口类对象
if (service == nullptr) {
ALOGE("Could not get passthrough implementation for %s/%s.",
Interface::descriptor, name.c_str());
return EXIT_FAILURE;
}
LOG_FATAL_IF(service->isRemote(), "Implementation of %s/%s is remote!",
Interface::descriptor, name.c_str());
status_t status = service->registerAsService(name);//将IComposer注册到hwservicemanager中
if (status == OK) {
ALOGI("Registration complete for %s/%s.",
Interface::descriptor, name.c_str());
} else {
ALOGE("Could not register service %s/%s (%d).",
Interface::descriptor, name.c_str(), status);
}
return status;
}
Hal进程获取IComposer类对象
在composer hal进程启动时，首先调用IComposer 的getService(“default”,true)来获取IComposer的类对象。
composer2.1android.hardware.graphics.composer@2.1_genc++genandroidhardwaregraphicscomposer2.1ComposerAll.cpp
::android::sp<IComposer> IComposer::getService(const std::string &serviceName, const bool getStub) {
using ::android::hardware::defaultServiceManager;
using ::android::hardware::details::waitForHwService;
using ::android::hardware::getPassthroughServiceManager;
using ::android::hardware::Return;
using ::android::sp;
using Transport = ::android::hidl::manager::V1_0::IServiceManager::Transport;
sp<IComposer> iface = nullptr;
const sp<::android::hidl::manager::V1_0::IServiceManager> sm = defaultServiceManager(); //获取hwservicemanager的代理
if (sm == nullptr) {
ALOGE("getService: defaultServiceManager() is null");
return nullptr;
}
Return<Transport> transportRet = sm->getTransport(IComposer::descriptor, serviceName);//查询IComposer的Transport
if (!transportRet.isOk()) {
ALOGE("getService: defaultServiceManager()->getTransport returns %s", transportRet.description().c_str());
return nullptr;
}
Transport transport = transportRet;
const bool vintfHwbinder = (transport == Transport::HWBINDER);
const bool vintfPassthru = (transport == Transport::PASSTHROUGH); //Transport类型判断
#ifdef __ANDROID_TREBLE__
#ifdef __ANDROID_DEBUGGABLE__
const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");
const bool trebleTestingOverride = env && !strcmp(env, "true");
const bool vintfLegacy = (transport == Transport::EMPTY) && trebleTestingOverride;
#else // __ANDROID_TREBLE__ but not __ANDROID_DEBUGGABLE__
const bool trebleTestingOverride = false;
const bool vintfLegacy = false;
#endif // __ANDROID_DEBUGGABLE__
#else // not __ANDROID_TREBLE__
const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");
const bool trebleTestingOverride = env && !strcmp(env, "true");
const bool vintfLegacy = (transport == Transport::EMPTY);
#endif // __ANDROID_TREBLE__
//hwbinder方式下获取IComposer对象
for (int tries = 0; !getStub && (vintfHwbinder || (vintfLegacy && tries == 0)); tries++) {
if (tries > 1) {
ALOGI("getService: Will do try %d for %s/%s in 1s...", tries, IComposer::descriptor, serviceName.c_str());
sleep(1);
}
if (vintfHwbinder && tries > 0) {
waitForHwService(IComposer::descriptor, serviceName);
}
Return<sp<::android::hidl::base::V1_0::IBase>> ret =
sm->get(IComposer::descriptor, serviceName);
if (!ret.isOk()) {
ALOGE("IComposer: defaultServiceManager()->get returns %s", ret.description().c_str());
break;
}
sp<::android::hidl::base::V1_0::IBase> base = ret;
if (base == nullptr) {
if (tries > 0) {
ALOGW("IComposer: found null hwbinder interface");
}continue;
}
Return<sp<IComposer>> castRet = IComposer::castFrom(base, true /* emitError */);
if (!castRet.isOk()) {
if (castRet.isDeadObject()) {
ALOGW("IComposer: found dead hwbinder service");
continue;
} else {
ALOGW("IComposer: cannot call into hwbinder service: %s; No permission? Check for selinux denials.", castRet.description().c_str());
break;
}
}
iface = castRet;
if (iface == nullptr) {
ALOGW("IComposer: received incompatible service; bug in hwservicemanager?");
break;
}
return iface;
}
//passthrough方式下获取IComposer对象
if (getStub || vintfPassthru || vintfLegacy) {
const sp<::android::hidl::manager::V1_0::IServiceManager> pm = getPassthroughServiceManager();
if (pm != nullptr) {
Return<sp<::android::hidl::base::V1_0::IBase>> ret =
pm->get(IComposer::descriptor, serviceName);
if (ret.isOk()) {
sp<::android::hidl::base::V1_0::IBase> baseInterface = ret;
if (baseInterface != nullptr) {
iface = IComposer::castFrom(baseInterface);
if (!getStub || trebleTestingOverride) {
iface = new BsComposer(iface);
}
}
}
}
}
return iface;
}
这里通过hwservicemanager获取当前服务的Tranport类型，Treble中定义的Tranport包括passthrough和binderized，每个hidl服务都在/system/manifest.xml或者/vendor/manifest.xml中指定了对应的Tranport类型：
manifest.xml文件的读取和解析都是由hwservicemanager来完成的，此时android.hardware.graphics.composer@2.1-service作为hwservicemanager的client端，通过hwservicemanager的binder代理对象来请求hwservicemanager进程查询IComposer的Transport类型，从上图可以看出IComposer的Transport被定义为hwbinder，因此：
vintfHwbinder=true
vintfPassthru=false
vintfLegacy=false
hidl服务对象获取方式包括2中：
1. 通过查询hwservicemanager来获取；
2.通过PassthroughServiceManager从本进程地址空间中获取；
那如何选择获取方式呢？ 其实就是vintfHwbinder、vintfPassthru、vintfLegacy、getStub这4个变量值来决定hidl服务的获取方式。
1. 当getStub为true时，不管hal属于什么传输模式，都采用PassthroughServiceManager获取接口对象；
2.当getStub为false时，则根据hal传输模式来选择接口获取方式；
《1》 当hal模式为Hwbinder时，则从hwservicemanager中查询；
《2》当hal传输模式为Passthru或Legacy时，则采用PassthroughServiceManager来获取；
那什么是Hwbinder，什么是Passthru及Legacy呢？下图是google提供的hal的roadmap图：
if (getStub || vintfPassthru || vintfLegacy) {
const sp<::android::hidl::manager::V1_0::IServiceManager> pm = getPassthroughServiceManager();
if (pm != nullptr) {
Return<sp<::android::hidl::base::V1_0::IBase>> ret =
pm->get(IComposer::descriptor, serviceName);
if (ret.isOk()) {
sp<::android::hidl::base::V1_0::IBase> baseInterface = ret;
if (baseInterface != nullptr) {
iface = IComposer::castFrom(baseInterface);
if (!getStub || trebleTestingOverride) {
iface = new BsComposer(iface);
}
}
}
}
}
sp<Interface> service = Interface::getService(name, true /* getStub */)所以getStub=true. 这里通过PassthroughServiceManager来获取IComposer对象。其实所有的Hal 进程都是通过PassthroughServiceManager来得到hidl服务对象的，而作为Hal进程的Client端Framework进程在获取hidl服务对象时，需要通过hal的Transport类型来选择获取方式。
systemlibhidl ransportServiceManagement.cpp
sp<IServiceManager> getPassthroughServiceManager() {
static sp<PassthroughServiceManager> manager(new PassthroughServiceManager());
return manager;
}
这里只是简单的创建了一个PassthroughServiceManager对象。PassthroughServiceManager也实现了IServiceManager接口。然后通过PassthroughServiceManager询服务：
Return<sp<IBase>> get(const hidl_string& fqName,
const hidl_string& name) override {
std::string stdFqName(fqName.c_str());
//fqName looks like android.hardware.foo@1.0::IFoo
size_t idx = stdFqName.find("::");
if (idx == std::string::npos ||
idx + strlen("::") + 1 >= stdFqName.size()) {
LOG(ERROR) << "Invalid interface name passthrough lookup: " << fqName;
return nullptr;
}
std::string packageAndVersion = stdFqName.substr(0, idx);
std::string ifaceName = stdFqName.substr(idx + strlen("::"));
const std::string prefix = packageAndVersion + "-impl";
const std::string sym = "HIDL_FETCH_" + ifaceName;
const android_namespace_t* sphal_namespace = android_get_exported_namespace("sphal");
const int dlMode = RTLD_LAZY;
void *handle = nullptr;
// TODO: lookup in VINTF instead
// TODO(b/34135607): Remove HAL_LIBRARY_PATH_SYSTEM
dlerror(); // clear
for (const std::string &path : {
HAL_LIBRARY_PATH_ODM, HAL_LIBRARY_PATH_VENDOR, HAL_LIBRARY_PATH_SYSTEM
}) {
std::vector<std::string> libs = search(path, prefix, ".so");
for (const std::string &lib : libs) {
const std::string fullPath = path + lib;
// If sphal namespace is available, try to load from the
// namespace first. If it fails, fall back to the original
// dlopen, which loads from the current namespace.
if (sphal_namespace != nullptr && path != HAL_LIBRARY_PATH_SYSTEM) {
const android_dlextinfo dlextinfo = {
.flags = ANDROID_DLEXT_USE_NAMESPACE,
// const_cast is dirty but required because
// library_namespace field is non-const.
.library_namespace = const_cast<android_namespace_t*>(sphal_namespace),
};
handle = android_dlopen_ext(fullPath.c_str(), dlMode, &dlextinfo);
if (handle == nullptr) {
const char* error = dlerror();
LOG(WARNING) << "Failed to dlopen " << lib << " from sphal namespace:"
<< (error == nullptr ? "unknown error" : error);
} else {
LOG(DEBUG) << lib << " loaded from sphal namespace.";
}
}
if (handle == nullptr) {
handle = dlopen(fullPath.c_str(), dlMode);
}
if (handle == nullptr) {
const char* error = dlerror();
LOG(ERROR) << "Failed to dlopen " << lib << ": "
<< (error == nullptr ? "unknown error" : error);
continue;
}
IBase* (*generator)(const char* name);
*(void **)(&generator) = dlsym(handle, sym.c_str());
if(!generator) {
const char* error = dlerror();
LOG(ERROR) << "Passthrough lookup opened " << lib
<< " but could not find symbol " << sym << ": "
<< (error == nullptr ? "unknown error" : error);
dlclose(handle);
continue;
}
IBase *interface = (*generator)(name.c_str());
if (interface == nullptr) {
dlclose(handle);
continue; // this module doesn't provide this instance name
}
registerReference(fqName, name);
return interface;
}
}
return nullptr;
}
根据传入的fqName=(android.hardware.graphics.composer@2.1::IComposer")获取当前的接口名IComposer，拼接出后面需要查找的函数名HIDL_FETCH_IComposer和库名字android.hardware.graphics.composer@2.1-impl.so,然后查找"/system/lib64/hw/"、"/vendor/lib64/hw/"、"/odm/lib64/hw/"下是否有对应的so库。接着通过dlopen载入/vendor/lib/hw/android.hardware.graphics.composer@2.1-impl.so，然后通过dlsym查找并调用HIDL_FETCH_IComposer函数，最后调用registerReference(fqName, name)向hwservicemanager注册。
hardware/interfaces/graphics/composer/2.1/default/Android.bp
cc_library_shared {
name: "android.hardware.graphics.composer@2.1-impl",
defaults: ["hidl_defaults"],
proprietary: true,
relative_install_path: "hw",
srcs: ["Hwc.cpp"],
static_libs: ["libhwcomposer-client"],
shared_libs: [
"android.hardware.graphics.composer@2.1",
"android.hardware.graphics.mapper@2.0",
"libbase",
"libcutils",
"libfmq",
"libhardware",
"libhidlbase",
"libhidltransport",
"liblog",
"libsync",
"libutils",
"libhwc2on1adapter"
],
}
从上面的编译脚本可知，android.hardware.graphics.composer@2.1-impl.so的源码文件为Hwc.cpp：
hardware/interfaces/graphics/composer/2.1/default/Hwc.cpp
IComposer* HIDL_FETCH_IComposer(const char*)
{
const hw_module_t* module = nullptr;
int err = hw_get_module(HWC_HARDWARE_MODULE_ID, &module);
if (err) {
ALOGE("failed to get hwcomposer module");
return nullptr;
}
return new HwcHal(module);
}
hw_get_module就和AndroidO以前的Hal模式一致，这正是Passthrough复用原有hal的原理。加载hal库后，得到hw_module_t，然后使用HwcHal来包裹hw_module_t，而HwcHal实现了IComposer接口。
registerPassthroughClient
得到IComposer接口对象HwcHal后，需要注册相关信息到hwservicemanager中。
systemlibhidl ransportServiceManagement.cpp
static void registerReference(const hidl_string &interfaceName, const hidl_string &instanceName) {
sp<IServiceManager> binderizedManager = defaultServiceManager();
if (binderizedManager == nullptr) {
LOG(WARNING) << "Could not registerReference for "
<< interfaceName << "/" << instanceName
<< ": null binderized manager.";
return;
}
auto ret = binderizedManager->registerPassthroughClient(interfaceName, instanceName);
if (!ret.isOk()) {
LOG(WARNING) << "Could not registerReference for "
<< interfaceName << "/" << instanceName
<< ": " << ret.description();
return;
}
LOG(VERBOSE) << "Successfully registerReference for "
<< interfaceName << "/" << instanceName;
}
这里通过hwservicemanager的代理对象跨进程调用registerPassthroughClient。
android.hidl.manager@1.0_genc++genandroidhidlmanager1.0ServiceManagerAll.cpp
::android::hardware::Return<void> BpHwServiceManager::registerPassthroughClient(const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name){
::android::hardware::Return<void> _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_registerPassthroughClient(this, this, fqName, name);
return _hidl_out;
}
::android::hardware::Return<void> BpHwServiceManager::_hidl_registerPassthroughClient(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();
#else
(void) _hidl_this_instrumentor;
#endif // __ANDROID_DEBUGGABLE__
atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::registerPassthroughClient::client");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)&fqName);
_hidl_args.push_back((void *)&name);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
::android::hardware::Parcel _hidl_data;
::android::hardware::Parcel _hidl_reply;
::android::status_t _hidl_err;
::android::hardware::Status _hidl_status;
_hidl_err = _hidl_data.writeInterfaceToken(BpHwServiceManager::descriptor);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
size_t _hidl_fqName_parent;
_hidl_err = _hidl_data.writeBuffer(&fqName, sizeof(fqName), &_hidl_fqName_parent);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::writeEmbeddedToParcel(
fqName,
&_hidl_data,
_hidl_fqName_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
size_t _hidl_name_parent;
_hidl_err = _hidl_data.writeBuffer(&name, sizeof(name), &_hidl_name_parent);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::writeEmbeddedToParcel(
name,
&_hidl_data,
_hidl_name_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(8 /* registerPassthroughClient */, _hidl_data, &_hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
if (!_hidl_status.isOk()) { return _hidl_status; }
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<void>();
_hidl_error:
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<void>(_hidl_status);
}
这里和普通binder通信相同，先就需要传输的函数参数打包到Parcel对象中，然后调用binder代理对象的transact函数将函数参数，函数调用码发送到Server端进程，这里的_hidl_this其实指向的是BpHwServiceManager，这个是与业务相关的代理对象，通过asBinder函数得到与传输相关的binder代理，那这个binder代理是什么类型呢？ 其实就是BpHwBinder，关于hwservicemanager代理对象的获取，asBinder函数的实现，在后续的章节中进行分析。经过BpHwServiceManager的请求，最终位于hwservicemanager进程中的BnHwServiceManager将接收函数调用请求：
android.hidl.manager@1.0_genc++genandroidhidlmanager1.0ServiceManagerAll.cpp
::android::status_t BnHwServiceManager::onTransact(
uint32_t _hidl_code,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
uint32_t _hidl_flags,
TransactCallback _hidl_cb) {
::android::status_t _hidl_err = ::android::OK;
switch (_hidl_code) {
case 8 /* registerPassthroughClient */:
{
_hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_registerPassthroughClient(this, _hidl_data, _hidl_reply, _hidl_cb);
break;
}
default:
{
return ::android::hidl::base::V1_0::BnHwBase::onTransact(
_hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);
}
}
BnHwServiceManager将调用_hidl_registerPassthroughClient来执行Client端的注册。
::android::status_t BnHwServiceManager::_hidl_registerPassthroughClient(
::android::hidl::base::V1_0::BnHwBase* _hidl_this,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
TransactCallback _hidl_cb) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();
#endif // __ANDROID_DEBUGGABLE__
::android::status_t _hidl_err = ::android::OK;
if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {
_hidl_err = ::android::BAD_TYPE;
return _hidl_err;
}
const ::android::hardware::hidl_string* fqName;
const ::android::hardware::hidl_string* name;
size_t _hidl_fqName_parent;
_hidl_err = _hidl_data.readBuffer(sizeof(*fqName), &_hidl_fqName_parent, reinterpret_cast<const void **>(&fqName));
if (_hidl_err != ::android::OK) { return _hidl_err; }
_hidl_err = ::android::hardware::readEmbeddedFromParcel(
const_cast<::android::hardware::hidl_string &>(*fqName),
_hidl_data,
_hidl_fqName_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { return _hidl_err; }
size_t _hidl_name_parent;
_hidl_err = _hidl_data.readBuffer(sizeof(*name), &_hidl_name_parent, reinterpret_cast<const void **>(&name));
if (_hidl_err != ::android::OK) { return _hidl_err; }
_hidl_err = ::android::hardware::readEmbeddedFromParcel(
const_cast<::android::hardware::hidl_string &>(*name),
_hidl_data,
_hidl_name_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { return _hidl_err; }
atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::registerPassthroughClient::server");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)fqName);
_hidl_args.push_back((void *)name);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
static_cast<BnHwServiceManager*>(_hidl_this)->_hidl_mImpl->registerPassthroughClient(*fqName, *name);
(void) _hidl_cb;
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);
return _hidl_err;
}
BnHwServiceManager首先读取BpHwServiceManager发送过来的函数参数，然后将registerPassthroughClient的执行转交个其成员变量的_hidl_mImpl对象，然后将执行结果返回给BpHwServiceManager，那么_hidl_mImpl保存的是什么对象呢？ 其实_hidl_mImpl指向的是ServiceManager对象，这个是在构造BnHwServiceManager对象时传入的，在后续分析hwservicemanager启动过程时，会进行详细分析。
systemhwservicemanagerServiceManager.cpp
Return<void> ServiceManager::registerPassthroughClient(const hidl_string &fqName,
const hidl_string &name) {
pid_t pid = IPCThreadState::self()->getCallingPid();
if (!mAcl.canGet(fqName, pid)) { //根据Client端的pid及注册接口的包名，判断是否有权限注册
/* We guard this function with "get", because it's typically used in
* the getService() path, albeit for a passthrough service in this
* case
*/
return Void();
}
LOG(INFO) << "registerPassthroughClient " << fgName.c_str() << " of "
<< name.c_str()
PackageInterfaceMap &ifaceMap = mServiceMap[fqName];
if (name.empty()) {
LOG(WARNING) << "registerPassthroughClient encounters empty instance name for "
<< fqName.c_str();
return Void();
}
HidlService *service = ifaceMap.lookup(name);
if (service == nullptr) {
auto adding = std::make_unique<HidlService>(fqName, name);
adding->registerPassthroughClient(pid);
ifaceMap.insertService(std::move(adding));
} else {
service->registerPassthroughClient(pid);
}
return Void();
}
首先根据fqName从mServiceMap中查找对应的PackageInterfaceMap，然后根据name从PackageInterfaceMap中查找HidlService，如果找不到对应的HidlService对象，那么就调用std::make_unique<HidlService>(fqName,name)创建一个新的HidlService对象，并ifaceMap.insertService(std::move(adding))添加到PackageInterfaceMap中。如果查找到了HidlService对象，那么仅仅将Client进程的pid保存到HidlService的mPassthroughClients变量中。
systemhwservicemanagerHidlService.h
HidlService(const std::string &interfaceName,
const std::string &instanceName)
: HidlService(
interfaceName,
instanceName,
nullptr,
static_cast<pid_t>(IServiceManager::PidConstant::NO_PID))
{}
因此registerPassthroughClient在hwservicemanager中插入一个HidlService对象而已，并没有注册对应的IBase对象。getService最后将HwcHal对象返回给registerPassthroughServiceImplementation()函数，然后再次调用registerAsService注册该IBase对象。
registerAsService注册
registerAsService用于向hwservicemanager注册IBase对象，由于前面通过PassthroughServiceManager得到的HwcHal继承于IBase，因此可以调用registerAsService函数来注册。
composer2.1android.hardware.graphics.composer@2.1_genc++genandroidhardwaregraphicscomposer2.1ComposerAll.cpp
::android::status_t IComposer::registerAsService(const std::string &serviceName) {
::android::hardware::details::onRegistration("android.hardware.graphics.composer@2.1", "IComposer", serviceName);
const ::android::sp<::android::hidl::manager::V1_0::IServiceManager> sm
= ::android::hardware::defaultServiceManager();
if (sm == nullptr) {
return ::android::INVALID_OPERATION;
}
::android::hardware::Return<bool> ret = sm->add(serviceName.c_str(), this);
return ret.isOk() && ret ? ::android::OK : ::android::UNKNOWN_ERROR;
}
首先执行onRegistration函数，然后调用hwservicemanager的代理对象的add函数。
systemlibhidl ransportServiceManagement.cpp
void onRegistration(const std::string &packageName,
const std::string& /* interfaceName */,
const std::string& /* instanceName */) {
tryShortenProcessName(packageName);
}
void tryShortenProcessName(const std::string &packageName) {
std::string processName = binaryName();
if (!startsWith(processName, packageName)) {
return;
}
// e.x. android.hardware.module.foo@1.0 -> foo@1.0
size_t lastDot = packageName.rfind('.');
size_t secondDot = packageName.rfind('.', lastDot - 1);
if (secondDot == std::string::npos) {
return;
}
std::string newName = processName.substr(secondDot + 1,
16 /* TASK_COMM_LEN */ - 1);
ALOGI("Removing namespace from process name %s to %s.",
processName.c_str(), newName.c_str());
int rc = pthread_setname_np(pthread_self(), newName.c_str());
ALOGI_IF(rc != 0, "Removing namespace from process name %s failed.",
processName.c_str());
}
这里只是简单的修改了当前进程的名称。
android.hidl.manager@1.0_genc++genandroidhidlmanager1.0ServiceManagerAll.cpp
::android::hardware::Return<bool> BpHwServiceManager::add(const ::android::hardware::hidl_string& name, const ::android::sp<::android::hidl::base::V1_0::IBase>& service){
::android::hardware::Return<bool> _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_add(this, this, name, service);
return _hidl_out;
}
::android::hardware::Return<bool> BpHwServiceManager::_hidl_add(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& name, const ::android::sp<::android::hidl::base::V1_0::IBase>& service) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();
#else
(void) _hidl_this_instrumentor;
#endif // __ANDROID_DEBUGGABLE__
atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::add::client");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)&name);
_hidl_args.push_back((void *)&service);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
::android::hardware::Parcel _hidl_data;
::android::hardware::Parcel _hidl_reply;
::android::status_t _hidl_err;
::android::hardware::Status _hidl_status;
bool _hidl_out_success;
_hidl_err = _hidl_data.writeInterfaceToken(BpHwServiceManager::descriptor);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
size_t _hidl_name_parent;
_hidl_err = _hidl_data.writeBuffer(&name, sizeof(name), &_hidl_name_parent);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::writeEmbeddedToParcel(
name,
&_hidl_data,
_hidl_name_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
if (service == nullptr) {
_hidl_err = _hidl_data.writeStrongBinder(nullptr);
} else {
::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<
::android::hidl::base::V1_0::IBase>(service);
if (_hidl_binder.get() != nullptr) {
_hidl_err = _hidl_data.writeStrongBinder(_hidl_binder);
} else {
_hidl_err = ::android::UNKNOWN_ERROR;
}
}
if (_hidl_err != ::android::OK) { goto _hidl_error; }
::android::hardware::ProcessState::self()->startThreadPool();
_hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(2 /* add */, _hidl_data, &_hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
if (!_hidl_status.isOk()) { return _hidl_status; }
_hidl_err = _hidl_reply.readBool(&_hidl_out_success);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)&_hidl_out_success);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<bool>(_hidl_out_success);
_hidl_error:
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<bool>(_hidl_status);
}
这里的步骤和前面的registerPassthroughClient基本一致，唯一不同的是，此时需要向Server端hwservicemanager传输一个IBase对象。
::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<
::android::hidl::base::V1_0::IBase>(service);
if (_hidl_binder.get() != nullptr) {
_hidl_err = _hidl_data.writeStrongBinder(_hidl_binder);
}
这里首先通过toBinder函数将IBase对象，其实就是HwcHal对象转换为IBinder对象，然后通过writeStrongBinder将IBinder对象序列化到Parcel中，toBinder函数在后续进行分析，我们这里只需要知道经过toBinder函数后，在Hal进程端会创建一个BnHwComposer本地binder对象，然后通过IPC调用发送给hwservicemanager。
android.hidl.manager@1.0_genc++genandroidhidlmanager1.0ServiceManagerAll.cpp
::android::status_t BnHwServiceManager::onTransact(
uint32_t _hidl_code,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
uint32_t _hidl_flags,
TransactCallback _hidl_cb) {
::android::status_t _hidl_err = ::android::OK;
switch (_hidl_code) {
case 2 /* add */:
{
_hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_add(this, _hidl_data, _hidl_reply, _hidl_cb);
break;
}
default:
{
return ::android::hidl::base::V1_0::BnHwBase::onTransact(
_hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);
}
}
if (_hidl_err == ::android::UNEXPECTED_NULL) {
_hidl_err = ::android::hardware::writeToParcel(
::android::hardware::Status::fromExceptionCode(::android::hardware::Status::EX_NULL_POINTER),
_hidl_reply);
}return _hidl_err;
}
::android::status_t BnHwServiceManager::_hidl_add(
::android::hidl::base::V1_0::BnHwBase* _hidl_this,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
TransactCallback _hidl_cb) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();
#endif // __ANDROID_DEBUGGABLE__
::android::status_t _hidl_err = ::android::OK;
if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {
_hidl_err = ::android::BAD_TYPE;
return _hidl_err;
}
const ::android::hardware::hidl_string* name;
::android::sp<::android::hidl::base::V1_0::IBase> service;
size_t _hidl_name_parent;
_hidl_err = _hidl_data.readBuffer(sizeof(*name), &_hidl_name_parent, reinterpret_cast<const void **>(&name));
if (_hidl_err != ::android::OK) { return _hidl_err; }
_hidl_err = ::android::hardware::readEmbeddedFromParcel(
const_cast<::android::hardware::hidl_string &>(*name),
_hidl_data,
_hidl_name_parent,
0 /* parentOffset */);
if (_hidl_err != ::android::OK) { return _hidl_err; }
{
::android::sp<::android::hardware::IBinder> _hidl_service_binder;
_hidl_err = _hidl_data.readNullableStrongBinder(&_hidl_service_binder);
if (_hidl_err != ::android::OK) { return _hidl_err; }
service = ::android::hardware::fromBinder<::android::hidl::base::V1_0::IBase,::android::hidl::base::V1_0::BpHwBase,::android::hidl::base::V1_0::BnHwBase>(_hidl_service_binder);
}
atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::add::server");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)name);
_hidl_args.push_back((void *)&service);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
bool _hidl_out_success = static_cast<BnHwServiceManager*>(_hidl_this)->_hidl_mImpl->add(*name, service);
::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);
_hidl_err = _hidl_reply->writeBool(_hidl_out_success);
/* _hidl_err ignored! */
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)&_hidl_out_success);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
_hidl_cb(*_hidl_reply);
return _hidl_err;
}
hwservicemanager进程通过_hidl_err = _hidl_data.readNullableStrongBinder(&_hidl_service_binder);拿到client进程发送过来的BnHwComposer对象，binder实体到达目的端进程将变为binder代理对象，然后通过fromBinder函数将binder代理对象转换为业务代理对象BpHwBase，这个过程在后续进行详细分析，接下来继续调用_hidl_mImpl的add函数，而我们知道_hidl_mImpl其实就是ServiceManager：
systemhwservicemanagerServiceManager.cpp
Return<bool> ServiceManager::add(const hidl_string& name, const sp<IBase>& service) {
bool isValidService = false;
if (service == nullptr) {
return false;
}
LOG(INFO) << "register service " << name;
// TODO(b/34235311): use HIDL way to determine this
// also, this assumes that the PID that is registering is the pid that is the service
pid_t pid = IPCThreadState::self()->getCallingPid();
auto ret = service->interfaceChain([&](const auto &interfaceChain) {
if (interfaceChain.size() == 0) {
return;
}
...
});
if (!ret.isOk()) {
LOG(ERROR) << "Failed to retrieve interface chain.";
return false;
}
return isValidService;
}
接着调用interfaceChain函数并传入一个函数回调，由于此时service是BpHwBase对象，BpHwBase的interfaceChain函数实现如下：
android.hidl.base@1.0_genc++genandroidhidlase1.0BaseAll.cpp
::android::hardware::Return<void> BpHwBase::interfaceChain(interfaceChain_cb _hidl_cb){
::android::hardware::Return<void> _hidl_out = ::android::hidl::base::V1_0::BpHwBase::_hidl_interfaceChain(this, this, _hidl_cb);
return _hidl_out;
}
::android::hardware::Return<void> BpHwBase::_hidl_interfaceChain(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, interfaceChain_cb _hidl_cb) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();
#else
(void) _hidl_this_instrumentor;
#endif // __ANDROID_DEBUGGABLE__
if (_hidl_cb == nullptr) {
return ::android::hardware::Status::fromExceptionCode(
::android::hardware::Status::EX_ILLEGAL_ARGUMENT,
"Null synchronous callback passed.");
}
atrace_begin(ATRACE_TAG_HAL, "HIDL::IBase::interfaceChain::client");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
::android::hardware::Parcel _hidl_data;
::android::hardware::Parcel _hidl_reply;
::android::status_t _hidl_err;
::android::hardware::Status _hidl_status;
const ::android::hardware::hidl_vec<::android::hardware::hidl_string>* _hidl_out_descriptors;
_hidl_err = _hidl_data.writeInterfaceToken(BpHwBase::descriptor);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(256067662 /* interfaceChain */, _hidl_data, &_hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
_hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
if (!_hidl_status.isOk()) { return _hidl_status; }
size_t _hidl__hidl_out_descriptors_parent;
_hidl_err = _hidl_reply.readBuffer(sizeof(*_hidl_out_descriptors), &_hidl__hidl_out_descriptors_parent, reinterpret_cast<const void **>(&_hidl_out_descriptors));
if (_hidl_err != ::android::OK) { goto _hidl_error; }
size_t _hidl__hidl_out_descriptors_child;
_hidl_err = ::android::hardware::readEmbeddedFromParcel(
const_cast<::android::hardware::hidl_vec<::android::hardware::hidl_string> &>(*_hidl_out_descriptors),
_hidl_reply,
_hidl__hidl_out_descriptors_parent,
0 /* parentOffset */, &_hidl__hidl_out_descriptors_child);
if (_hidl_err != ::android::OK) { goto _hidl_error; }
for (size_t _hidl_index_0 = 0; _hidl_index_0 < _hidl_out_descriptors->size(); ++_hidl_index_0) {
_hidl_err = ::android::hardware::readEmbeddedFromParcel(
const_cast<::android::hardware::hidl_string &>((*_hidl_out_descriptors)[_hidl_index_0]),
_hidl_reply,
_hidl__hidl_out_descriptors_child,
_hidl_index_0 * sizeof(::android::hardware::hidl_string));
if (_hidl_err != ::android::OK) { goto _hidl_error; }
}
_hidl_cb(*_hidl_out_descriptors);
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)_hidl_out_descriptors);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<void>();
_hidl_error:
_hidl_status.setFromStatusT(_hidl_err);
return ::android::hardware::Return<void>(_hidl_status);
}
这里再次回到Hal进程空间，调用BnHwComposer的interfaceChain函数查询_hidl_out_descriptors，
然后调用传递进来的回调函数_hidl_cb。因此BnHwComposer的onTransact将接收请求：
composer2.1android.hardware.graphics.composer@2.1_genc++genandroidhardwaregraphicscomposer2.1ComposerAll.cpp
::android::status_t BnHwComposer::onTransact(
uint32_t _hidl_code,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
uint32_t _hidl_flags,
TransactCallback _hidl_cb) {
::android::status_t _hidl_err = ::android::OK;
switch (_hidl_code) {
case 256067662 /* interfaceChain */:
{
_hidl_err = ::android::hidl::base::V1_0::BnHwBase::_hidl_interfaceChain(this, _hidl_data, _hidl_reply, _hidl_cb);
break;
}
default:
{
return ::android::hidl::base::V1_0::BnHwBase::onTransact(
_hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);
}
}
if (_hidl_err == ::android::UNEXPECTED_NULL) {
_hidl_err = ::android::hardware::writeToParcel(
::android::hardware::Status::fromExceptionCode(::android::hardware::Status::EX_NULL_POINTER),
_hidl_reply);
}return _hidl_err;
}
注意，onTransact的最后一个参数是一个回调函数，是由IPCThreadState传递进来的，该回调函数将传入BnHwBase的interfaceChain中执行。这个实现由其父类BnHwBase来完成：
android.hidl.base@1.0_genc++genandroidhidlase1.0BaseAll.cpp
::android::status_t BnHwBase::_hidl_interfaceChain(
BnHwBase* _hidl_this,
const ::android::hardware::Parcel &_hidl_data,
::android::hardware::Parcel *_hidl_reply,
TransactCallback _hidl_cb) {
#ifdef __ANDROID_DEBUGGABLE__
bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();
const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();
#endif // __ANDROID_DEBUGGABLE__
::android::status_t _hidl_err = ::android::OK;
if (!_hidl_data.enforceInterface(BnHwBase::Pure::descriptor)) {
_hidl_err = ::android::BAD_TYPE;
return _hidl_err;
}
atrace_begin(ATRACE_TAG_HAL, "HIDL::IBase::interfaceChain::server");
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
bool _hidl_callbackCalled = false;
static_cast<BnHwBase*>(_hidl_this)->_hidl_mImpl->interfaceChain([&](const auto &_hidl_out_descriptors) {
...
});
if (!_hidl_callbackCalled) {
LOG_ALWAYS_FATAL("interfaceChain: _hidl_cb not called, but must be called once.");
}
return _hidl_err;
}
BnHwBase的interfaceChain实现又转交给_hidl_mImpl，同时也传入一个匿名的回调函数，而BnHwBase的_hidl_mImpl保存的是HwcHal对象，HwcHal并没有实现该函数，该函数由其父类IComposer类实现。
composer2.1android.hardware.graphics.composer@2.1_genc++genandroidhardwaregraphicscomposer2.1ComposerAll.cpp
::android::hardware::Return<void> IComposer::interfaceChain(interfaceChain_cb _hidl_cb){
_hidl_cb({
IComposer::descriptor,
::android::hidl::base::V1_0::IBase::descriptor,
});
return ::android::hardware::Void();}
这里只是回调由BnHwBase传进来的回调函数，且函数参数是IComposer::descriptor, IBase::descriptor。回调函数实现如下：
{
if (_hidl_callbackCalled) {
LOG_ALWAYS_FATAL("interfaceChain: _hidl_cb called a second time, but must be called once.");
}
_hidl_callbackCalled = true;
::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);
size_t _hidl__hidl_out_descriptors_parent;
_hidl_err = _hidl_reply->writeBuffer(&_hidl_out_descriptors, sizeof(_hidl_out_descriptors), &_hidl__hidl_out_descriptors_parent);
/* _hidl_err ignored! */
size_t _hidl__hidl_out_descriptors_child;
_hidl_err = ::android::hardware::writeEmbeddedToParcel(
_hidl_out_descriptors,
_hidl_reply,
_hidl__hidl_out_descriptors_parent,
0 /* parentOffset */, &_hidl__hidl_out_descriptors_child);
/* _hidl_err ignored! */
for (size_t _hidl_index_0 = 0; _hidl_index_0 < _hidl_out_descriptors.size(); ++_hidl_index_0) {
_hidl_err = ::android::hardware::writeEmbeddedToParcel(
_hidl_out_descriptors[_hidl_index_0],
_hidl_reply,
_hidl__hidl_out_descriptors_child,
_hidl_index_0 * sizeof(::android::hardware::hidl_string));
/* _hidl_err ignored! */
}
atrace_end(ATRACE_TAG_HAL);
#ifdef __ANDROID_DEBUGGABLE__
if (UNLIKELY(mEnableInstrumentation)) {
std::vector<void *> _hidl_args;
_hidl_args.push_back((void *)&_hidl_out_descriptors);
for (const auto &callback: mInstrumentationCallbacks) {
callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);
}
}
#endif // __ANDROID_DEBUGGABLE__
_hidl_cb(*_hidl_reply);
}
这里只是将回调函数的参数IComposer::descriptor,IBase::descriptor打包到Parcel对象中，然后继续调用由IPCThreadState传进入的回调函数，该回调实现如下：
systemlibhwbinderIPCThreadState.cpp
auto reply_callback = [&] (auto &replyParcel) {
if (reply_sent) {
// Reply was sent earlier, ignore it.
ALOGE("Dropping binder reply, it was sent already.");
return;
}
reply_sent = true;
if ((tr.flags & TF_ONE_WAY) == 0) {
replyParcel.setError(NO_ERROR);
sendReply(replyParcel, 0);
} else {
ALOGE("Not sending reply in one-way transaction");
}
};
该回调函数只是将打包后的Parcel发送给hwservicemanager进程。
也就是说，hwservicemanager将得到IComposer::descriptor,IBase::descriptor，BpHwBase读取到这些数据后，接着会回调由ServiceManager传入进来的回调函数：
systemhwservicemanagerServiceManager.cpp
{
if (interfaceChain.size() == 0) {
return;
}
// First, verify you're allowed to add() the whole interface hierarchy
for(size_t i = 0; i < interfaceChain.size(); i++) {
std::string fqName = interfaceChain[i];
if (!mAcl.canAdd(fqName, pid)) {
return;
}
}
for(size_t i = 0; i < interfaceChain.size(); i++) {
std::string fqName = interfaceChain[i];
LOG(INFO) << "add service of " << fqName;
PackageInterfaceMap &ifaceMap = mServiceMap[fqName];
HidlService *hidlService = ifaceMap.lookup(name);
if (hidlService == nullptr) {
LOG(INFO) << "insertService " << name << " of " << fgName ;
ifaceMap.insertService(
std::make_unique<HidlService>(fqName, name, service, pid));
} else {
if (hidlService->getService() != nullptr) {
auto ret = hidlService->getService()->unlinkToDeath(this);
ret.isOk(); // ignore
}
LOG(INFO) << "setService " << " of " << fgName ;
hidlService->setService(service, pid);
}
ifaceMap.sendPackageRegistrationNotification(fqName, name);
}
auto linkRet = service->linkToDeath(this, 0 /*cookie*/);
linkRet.isOk(); // ignore
isValidService = true;
}
该回调函数的参数值其实就是从Hal进程传递过来的IComposer::descriptor,IBase::descriptor，这时就开始完成服务注册了，整个服务注册过程分为三个步骤：
1. 服务校验过程
2. 服务添加过程
3. 死亡通知注册过程
服务校验
AccessControl类主要负责权限检查，包括SELinux权限。
systemhwservicemanagerAccessControl.cpp
AccessControl::AccessControl() {
mSeHandle = selinux_android_hw_service_context_handle();
LOG_ALWAYS_FATAL_IF(mSeHandle == NULL, "Failed to acquire SELinux handle.");
if (getcon(&mSeContext) != 0) {
LOG_ALWAYS_FATAL("Failed to acquire hwservicemanager context.");
}
selinux_status_open(true);
mSeCallbacks.func_audit = AccessControl::auditCallback;
selinux_set_callback(SELINUX_CB_AUDIT, mSeCallbacks);
mSeCallbacks.func_log = selinux_log_callback; /* defined in libselinux */
selinux_set_callback(SELINUX_CB_LOG, mSeCallbacks);
}
判断是否有权限添加过程如下：
bool AccessControl::canAdd(const std::string& fqName, pid_t pid) {
FQName fqIface(fqName);
if (!fqIface.isValid()) {
return false;
}
const std::string checkName = fqIface.package() + "::" + fqIface.name();
return checkPermission(pid, kPermissionAdd, checkName.c_str());
}
system oolshidlutilsFQName.cpp
FQName::FQName(const std::vector<std::string> &names)
: mValid(false),
mIsIdentifier(false) {
setTo(StringHelper::JoinStrings(names, "."));
}
bool FQName::setTo(const std::string &s) {
clearVersion();
mPackage.clear();
mName.clear();
mValid = true;
std::smatch match;
if (std::regex_match(s, match, kRE1)) {
CHECK_EQ(match.size(), 5u);
mPackage = match.str(1);
parseVersion(match.str(2), match.str(3));
mName = match.str(4);
} else if (std::regex_match(s, match, kRE2)) {
CHECK_EQ(match.size(), 4u);
parseVersion(match.str(1), match.str(2));
mName = match.str(3);
} else if (std::regex_match(s, match, kRE3)) {
CHECK_EQ(match.size(), 4u);
mPackage = match.str(1);
parseVersion(match.str(2), match.str(3));
} else if (std::regex_match(s, match, kRE4)) {
mName = match.str(0);
} else if (std::regex_match(s, match, kRE5)) {
mIsIdentifier = true;
mName = match.str(0);
} else if (std::regex_match(s, match, kRE6)) {
CHECK_EQ(match.size(), 6u);
mPackage = match.str(1);
parseVersion(match.str(2), match.str(3));
mName = match.str(4);
mValueName = match.str(5);
} else if (std::regex_match(s, match, kRE7)) {
CHECK_EQ(match.size(), 5u);
parseVersion(match.str(1), match.str(2));
mName = match.str(3);
mValueName = match.str(4);
} else if (std::regex_match(s, match, kRE8)) {
CHECK_EQ(match.size(), 3u);
mName = match.str(1);
mValueName = match.str(2);
} else {
mValid = false;
}
// mValueName must go with mName.
CHECK(mValueName.empty() || !mName.empty());
// package without version is not allowed.
CHECK(mPackage.empty() || !version().empty());
return isValid();
}
setTo函数其实就是使用正则表达式从android.hidl.manager@1.0::IServiceManager字符串中取出包名，版本号，及服务类名，从而检查包名是否符合命名规则，如果包名有效，则继续调用checkPermission函数来检查selinux权限。
bool AccessControl::checkPermission(pid_t sourcePid, const char *targetContext,
const char *perm, const char *interface) {
char *sourceContext = NULL;
bool allowed = false;
struct audit_data ad;
if (getpidcon(sourcePid, &sourceContext) < 0) {
ALOGE("SELinux: failed to retrieved process context for pid %d", sourcePid);
return false;
}
ad.pid = sourcePid;
ad.interfaceName = interface;
allowed = (selinux_check_access(sourceContext, targetContext, "hwservice_manager",
perm, (void *) &ad) == 0);
freecon(sourceContext);
return allowed;
}
服务注册
如果服务注册进程有权限向hwservicemanager注册服务，接下来将完成服务添加。
每个服务接口对应多个实例，比如android.hidl.manager@1.1::IServiceManager可以注册多个实例，每个实例名称不同。
PackageInterfaceMap &ifaceMap = mServiceMap[fqName];
HidlService *hidlService = ifaceMap.lookup(name);
const HidlService *ServiceManager::PackageInterfaceMap::lookup(
const std::string &name) const {
auto it = mInstanceMap.find(name);
if (it == mInstanceMap.end()) {
return nullptr;
}
return it->second.get();
}
根据名称查找HidlService，如果找不到，则新增一个HidlService，如果已经存在，则更新service。
if (hidlService == nullptr) {
LOG(INFO) << "insertService " << name << " of " << fgName ;
ifaceMap.insertService(
std::make_unique<HidlService>(fqName, name, service, pid));
} else {
if (hidlService->getService() != nullptr) {
auto ret = hidlService->getService()->unlinkToDeath(this);
ret.isOk(); // ignore
}
LOG(INFO) << "setService " << " of " << fgName ;
hidlService->setService(service, pid);
}
到此就完成了hidl服务注册。