本文轉載自:https://blog.csdn.net/yangwen123/article/details/79854267
通過前面對Treble架構的介紹，我們知道，Android Framework進程和Hal分離，每個Hal獨立運行在自己的進程地址空間，那么這些Hal進程是如何啟動的呢？本文以composer hal為例展開分析。
在以下路徑有composer hal的rc啟動腳本：
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
編譯后，會將該腳本文件copy到vendor/etc/init目錄，在開機時，init進程會讀取並解析這個腳本，然后啟動android.hardware.graphics.composer@2.1-service進程：
system 661 1 32288 7832 0 0 S android.hardware.graphics.composer@2.1-service
該進程的可執行文件是：vendor/bin/hw/android.hardware.graphics.composer@2.1-service，
該可執行文件對應的源碼為：hardware/interfaces/graphics/composer/2.1/default/service.cpp
composer Hal啟動過程
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);
}
前面我們分析了Treble架構下的binder通信變化，在Treble架構下，存在了3個binder設備，分別是/dev/binder、/dev/vndbinder、/dev/hwbinder，上層需要通過binder庫來訪問這些binder設備，而/dev/binder和/dev/vndbinder都是由libbinder來訪問，因此需要指定打開的binder設備。
android::ProcessState::initWithDriver("/dev/vndbinder");
這句說明composer hal通過vndbinder來通信的，接下來就是設置binder線程個數為4，並啟動binder線程池，然后調用
defaultPassthroughServiceImplementation<IComposer>(4)
完成composer hal的啟動。
system\libhidl\transport\include\hidl\LegacySupport.h
template<class Interface>
__attribute__((warn_unused_result))
status_t defaultPassthroughServiceImplementation(std::string name,
size_t maxThreads = 1) {
configureRpcThreadpool(maxThreads, true); //配置binder線程個數
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 */); //從當前進程空間中拿到IComposer接口類對象
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);//將IComposer注冊到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進程獲取IComposer類對象
在composer hal進程啟動時，首先調用IComposer 的getService(“default”,true)來獲取IComposer的類對象。
composer\2.1\android.hardware.graphics.composer@2.1_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.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(); //獲取hwservicemanager的代理
if (sm == nullptr) {
ALOGE("getService: defaultServiceManager() is null");
return nullptr;
}
Return<Transport> transportRet = sm->getTransport(IComposer::descriptor, serviceName);//查詢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類型判斷
#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方式下獲取IComposer對象
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方式下獲取IComposer對象
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;
}
這里通過hwservicemanager獲取當前服務的Tranport類型，Treble中定義的Tranport包括passthrough和binderized，每個hidl服務都在/system/manifest.xml或者/vendor/manifest.xml中指定了對應的Tranport類型：
manifest.xml文件的讀取和解析都是由hwservicemanager來完成的，此時android.hardware.graphics.composer@2.1-service作為hwservicemanager的client端，通過hwservicemanager的binder代理對象來請求hwservicemanager進程查詢IComposer的Transport類型，從上圖可以看出IComposer的Transport被定義為hwbinder，因此：
vintfHwbinder=true
vintfPassthru=false
vintfLegacy=false
hidl服務對象獲取方式包括2中：
1. 通過查詢hwservicemanager來獲取；
2.通過PassthroughServiceManager從本進程地址空間中獲取；
那如何選擇獲取方式呢？ 其實就是vintfHwbinder、vintfPassthru、vintfLegacy、getStub這4個變量值來決定hidl服務的獲取方式。
1. 當getStub為true時，不管hal屬於什么傳輸模式，都采用PassthroughServiceManager獲取接口對象；
2.當getStub為false時，則根據hal傳輸模式來選擇接口獲取方式；
《1》 當hal模式為Hwbinder時，則從hwservicemanager中查詢；
《2》當hal傳輸模式為Passthru或Legacy時，則采用PassthroughServiceManager來獲取；
那什么是Hwbinder，什么是Passthru及Legacy呢？下圖是google提供的hal的roadmap圖：
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. 這里通過PassthroughServiceManager來獲取IComposer對象。其實所有的Hal 進程都是通過PassthroughServiceManager來得到hidl服務對象的，而作為Hal進程的Client端Framework進程在獲取hidl服務對象時，需要通過hal的Transport類型來選擇獲取方式。
system\libhidl\transport\ServiceManagement.cpp
sp<IServiceManager> getPassthroughServiceManager() {
static sp<PassthroughServiceManager> manager(new PassthroughServiceManager());
return manager;
}
這里只是簡單的創建了一個PassthroughServiceManager對象。PassthroughServiceManager也實現了IServiceManager接口。然后通過PassthroughServiceManager詢服務：
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;
}
根據傳入的fqName=(android.hardware.graphics.composer@2.1::IComposer")獲取當前的接口名IComposer，拼接出后面需要查找的函數名HIDL_FETCH_IComposer和庫名字android.hardware.graphics.composer@2.1-impl.so,然后查找"/system/lib64/hw/"、"/vendor/lib64/hw/"、"/odm/lib64/hw/"下是否有對應的so庫。接着通過dlopen載入/vendor/lib/hw/android.hardware.graphics.composer@2.1-impl.so，然后通過dlsym查找並調用HIDL_FETCH_IComposer函數，最后調用registerReference(fqName, name)向hwservicemanager注冊。
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"
],
}
從上面的編譯腳本可知，android.hardware.graphics.composer@2.1-impl.so的源碼文件為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，這正是Passthrough復用原有hal的原理。加載hal庫后，得到hw_module_t，然后使用HwcHal來包裹hw_module_t，而HwcHal實現了IComposer接口。
registerPassthroughClient
得到IComposer接口對象HwcHal后，需要注冊相關信息到hwservicemanager中。
system\libhidl\transport\ServiceManagement.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;
}
這里通過hwservicemanager的代理對象跨進程調用registerPassthroughClient。
android.hidl.manager@1.0_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.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);
}
這里和普通binder通信相同，先就需要傳輸的函數參數打包到Parcel對象中，然后調用binder代理對象的transact函數將函數參數，函數調用碼發送到Server端進程，這里的_hidl_this其實指向的是BpHwServiceManager，這個是與業務相關的代理對象，通過asBinder函數得到與傳輸相關的binder代理，那這個binder代理是什么類型呢？ 其實就是BpHwBinder，關於hwservicemanager代理對象的獲取，asBinder函數的實現，在后續的章節中進行分析。經過BpHwServiceManager的請求，最終位於hwservicemanager進程中的BnHwServiceManager將接收函數調用請求：
android.hidl.manager@1.0_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.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將調用_hidl_registerPassthroughClient來執行Client端的注冊。
::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首先讀取BpHwServiceManager發送過來的函數參數，然后將registerPassthroughClient的執行轉交個其成員變量的_hidl_mImpl對象，然后將執行結果返回給BpHwServiceManager，那么_hidl_mImpl保存的是什么對象呢？ 其實_hidl_mImpl指向的是ServiceManager對象，這個是在構造BnHwServiceManager對象時傳入的，在后續分析hwservicemanager啟動過程時，會進行詳細分析。
system\hwservicemanager\ServiceManager.cpp
Return<void> ServiceManager::registerPassthroughClient(const hidl_string &fqName,
const hidl_string &name) {
pid_t pid = IPCThreadState::self()->getCallingPid();
if (!mAcl.canGet(fqName, pid)) { //根據Client端的pid及注冊接口的包名，判斷是否有權限注冊
/* 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();
}
首先根據fqName從mServiceMap中查找對應的PackageInterfaceMap，然后根據name從PackageInterfaceMap中查找HidlService，如果找不到對應的HidlService對象，那么就調用std::make_unique<HidlService>(fqName,name)創建一個新的HidlService對象，並ifaceMap.insertService(std::move(adding))添加到PackageInterfaceMap中。如果查找到了HidlService對象，那么僅僅將Client進程的pid保存到HidlService的mPassthroughClients變量中。
system\hwservicemanager\HidlService.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中插入一個HidlService對象而已，並沒有注冊對應的IBase對象。getService最后將HwcHal對象返回給registerPassthroughServiceImplementation()函數，然后再次調用registerAsService注冊該IBase對象。
registerAsService注冊
registerAsService用於向hwservicemanager注冊IBase對象，由於前面通過PassthroughServiceManager得到的HwcHal繼承於IBase，因此可以調用registerAsService函數來注冊。
composer\2.1\android.hardware.graphics.composer@2.1_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.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;
}
首先執行onRegistration函數，然后調用hwservicemanager的代理對象的add函數。
system\libhidl\transport\ServiceManagement.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());
}
這里只是簡單的修改了當前進程的名稱。
android.hidl.manager@1.0_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.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);
}
這里的步驟和前面的registerPassthroughClient基本一致，唯一不同的是，此時需要向Server端hwservicemanager傳輸一個IBase對象。
::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);
}
這里首先通過toBinder函數將IBase對象，其實就是HwcHal對象轉換為IBinder對象，然后通過writeStrongBinder將IBinder對象序列化到Parcel中，toBinder函數在后續進行分析，我們這里只需要知道經過toBinder函數后，在Hal進程端會創建一個BnHwComposer本地binder對象，然后通過IPC調用發送給hwservicemanager。
android.hidl.manager@1.0_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.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進程通過_hidl_err = _hidl_data.readNullableStrongBinder(&_hidl_service_binder);拿到client進程發送過來的BnHwComposer對象，binder實體到達目的端進程將變為binder代理對象，然后通過fromBinder函數將binder代理對象轉換為業務代理對象BpHwBase，這個過程在后續進行詳細分析，接下來繼續調用_hidl_mImpl的add函數，而我們知道_hidl_mImpl其實就是ServiceManager：
system\hwservicemanager\ServiceManager.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;
}
接着調用interfaceChain函數並傳入一個函數回調，由於此時service是BpHwBase對象，BpHwBase的interfaceChain函數實現如下：
android.hidl.base@1.0_genc++\gen\android\hidl\base\1.0\BaseAll.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);
}
這里再次回到Hal進程空間，調用BnHwComposer的interfaceChain函數查詢_hidl_out_descriptors，
然后調用傳遞進來的回調函數_hidl_cb。因此BnHwComposer的onTransact將接收請求：
composer\2.1\android.hardware.graphics.composer@2.1_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.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的最后一個參數是一個回調函數，是由IPCThreadState傳遞進來的，該回調函數將傳入BnHwBase的interfaceChain中執行。這個實現由其父類BnHwBase來完成：
android.hidl.base@1.0_genc++\gen\android\hidl\base\1.0\BaseAll.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實現又轉交給_hidl_mImpl，同時也傳入一個匿名的回調函數，而BnHwBase的_hidl_mImpl保存的是HwcHal對象，HwcHal並沒有實現該函數，該函數由其父類IComposer類實現。
composer\2.1\android.hardware.graphics.composer@2.1_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.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();}
這里只是回調由BnHwBase傳進來的回調函數，且函數參數是IComposer::descriptor, IBase::descriptor。回調函數實現如下：
{
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);
}
這里只是將回調函數的參數IComposer::descriptor,IBase::descriptor打包到Parcel對象中，然后繼續調用由IPCThreadState傳進入的回調函數，該回調實現如下：
system\libhwbinder\IPCThreadState.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");
}
};
該回調函數只是將打包后的Parcel發送給hwservicemanager進程。
也就是說，hwservicemanager將得到IComposer::descriptor,IBase::descriptor，BpHwBase讀取到這些數據后，接着會回調由ServiceManager傳入進來的回調函數：
system\hwservicemanager\ServiceManager.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;
}
該回調函數的參數值其實就是從Hal進程傳遞過來的IComposer::descriptor,IBase::descriptor，這時就開始完成服務注冊了，整個服務注冊過程分為三個步驟：
1. 服務校驗過程
2. 服務添加過程
3. 死亡通知注冊過程
服務校驗
AccessControl類主要負責權限檢查，包括SELinux權限。
system\hwservicemanager\AccessControl.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);
}
判斷是否有權限添加過程如下：
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\tools\hidl\utils\FQName.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函數其實就是使用正則表達式從android.hidl.manager@1.0::IServiceManager字符串中取出包名，版本號，及服務類名，從而檢查包名是否符合命名規則，如果包名有效，則繼續調用checkPermission函數來檢查selinux權限。
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;
}
服務注冊
如果服務注冊進程有權限向hwservicemanager注冊服務，接下來將完成服務添加。
每個服務接口對應多個實例，比如android.hidl.manager@1.1::IServiceManager可以注冊多個實例，每個實例名稱不同。
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();
}
根據名稱查找HidlService，如果找不到，則新增一個HidlService，如果已經存在，則更新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服務注冊。