在 Android O 中,系統啓動時,就會啓動 CameraProvider 服務。它將 Camera HAL 從 cameraserver 進程中分離出來,作爲一個獨立進程 [email protected] 來控制 HAL。
這兩個進程之間通過 HIDL 機制進行通信。
這樣的改動源自於 Android O 版本加入的 Treble 機制,它的主要功能(如下圖所示)是將 service 與 HAL 隔離,以方便 HAL 部分進行獨立升級。這其實和 APP 與 Framework 之間的 Binder 機制類似,通過引入一個進程間通信機制而針對不同層級進行解耦(從 Local call 變成了 Remote call)。
下面以Android P進行相應的學習分析。
camera provider 啓動
-
android/hardware/interfaces/camera/provider/2.4/default/[email protected]
service vendor.camera-provider-2-4 /vendor/bin/hw/[email protected] class hal user cameraserver group audio camera input drmrpc ioprio rt 4 capabilities SYS_NICE writepid /dev/cpuset/camera-daemon/tasks /dev/stune/top-app/tasks
在android啓動的過程中,init進程調用該腳本啓動 camera provider 服務。根據該目錄下的 Android.bp 可以知道,其實就是運行該目錄下 service.cpp 編譯的可執行文件,service.cpp 內容如下:
int main()
{
ALOGI("Camera provider Service is starting.");
// The camera HAL may communicate to other vendor components via
// /dev/vndbinder
android::ProcessState::initWithDriver("/dev/vndbinder");
return defaultPassthroughServiceImplementation<ICameraProvider>("legacy/0", /*maxThreads*/ 6);
}
根據以上代碼可以得知:
- android::ProcessState::initWithDriver :camera HAL 通過
/dev/vndbinder
驅動可與其他模塊的HAL進行通信; - defaultPassthroughServiceImplementation :創建默認爲直通模式(passthrough)的 CameraProvider 服務;
LegacySupport.h
文件路徑:android/system/libhidl/transport/include/hidl
/**
* Registers passthrough service implementation.
*/
template<class Interface>
__attribute__((warn_unused_result))
status_t registerPassthroughServiceImplementation(
std::string name = "default") {
/* 獲得CameraProvider實例化對象(不是Binder代理),(此處的name爲 “legacy/0”) */
sp<Interface> service = Interface::getService(name, true /* getStub */);
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());
/* 將 CameraProvider 註冊爲一個服務,其他進程需要使用camera HAL層時,通過Binder
* 得到 CameraProvider 代理類即可操作 camera HAL層,不需要每次都dlopen(HAL.so)
* */
status_t status = service->registerAsService(name);
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;
}
獲取 CameraProvider 實例對象
從 LegacySupport.h 可以知道,defaultPassthroughServiceImplementation爲模板類函數,將會通過 sp<ICameraProvider> service = ICameraProvider::getService(name, true /* getStub */)
獲取 CameraProvider 實例化對象,以上操作,將會進入 CameraProviderAll.cpp。
CameraProviderAll.cpp
文件路徑:android/out/soong/.intermediates/hardware/interfaces/camera/provider/2.4/[email protected]_genc++/gen/android/hardware/camera/provider/2.4
// static
::android::sp<ICameraProvider> ICameraProvider::getService(const std::string &serviceName, const bool getStub) {
return ::android::hardware::details::getServiceInternal<BpHwCameraProvider>(serviceName, true, getStub);
}
HidlTransportSupport.h
文件路徑:android/system/libhidl/transport/include/hidl
template <typename BpType, typename IType = typename BpType::Pure,
typename = std::enable_if_t<std::is_same<i_tag, typename IType::_hidl_tag>::value>,
typename = std::enable_if_t<std::is_same<bphw_tag, typename BpType::_hidl_tag>::value>>
sp<IType> getServiceInternal(const std::string& instance, bool retry, bool getStub) {
using ::android::hidl::base::V1_0::IBase;
sp<IBase> base = getRawServiceInternal(IType::descriptor, instance, retry, getStub);
if (base == nullptr) {
return nullptr;
}
if (base->isRemote()) {
// getRawServiceInternal guarantees we get the proper class
return sp<IType>(new BpType(toBinder<IBase>(base)));
}
return IType::castFrom(base);
}
其中,參數 BpHwCameraProvider::descriptor 爲[email protected]::ICameraProvider,instance 爲 “legacy/0” ,retry 爲 true,getStub 爲 true。
ServiceManagement.cpp
文件路徑:android/system/libhidl/transport
在調用 getRawServiceInternal() 函數時,由於我們的參數 getStub 爲 true,所以,該函數主要執行以下部分:
sp<::android::hidl::base::V1_0::IBase> getRawServiceInternal(const std::string& descriptor,
const std::string& instance,
bool retry, bool getStub) {
...
/* getStub 爲 true,直通模式,將返回CameraProvider實例對象 */
if (getStub || vintfPassthru || vintfLegacy) {
/* 獲取ServiceManager代理 */
const sp<IServiceManager> pm = getPassthroughServiceManager();
if (pm != nullptr) {
/* 獲取CameraProvider實例對象 */
sp<IBase> base = pm->get(descriptor, instance).withDefault(nullptr);
if (!getStub || trebleTestingOverride) {
base = wrapPassthrough(base);
}
return base;
}
}
return nullptr;
}
struct PassthroughServiceManager : IServiceManager1_1 {
static void openLibs(
const std::string& fqName,
const std::function<bool /* continue */ (void* /* handle */, const std::string& /* lib */,
const std::string& /* sym */)>& eachLib) {
//fqName looks like [email protected]::IFoo
/* fqName = [email protected]::ICameraProvider */
size_t idx = fqName.find("::");
if (idx == std::string::npos ||
idx + strlen("::") + 1 >= fqName.size()) {
LOG(ERROR) << "Invalid interface name passthrough lookup: " << fqName;
return;
}
std::string packageAndVersion = fqName.substr(0, idx);
std::string ifaceName = fqName.substr(idx + strlen("::"));
/* prefix = [email protected] */
const std::string prefix = packageAndVersion + "-impl";
/* sym = HIDL_FETCH_ICameraProvider */
const std::string sym = "HIDL_FETCH_" + ifaceName;
constexpr int dlMode = RTLD_LAZY;
void* handle = nullptr;
dlerror(); // clear
static std::string halLibPathVndkSp = android::base::StringPrintf(
HAL_LIBRARY_PATH_VNDK_SP_FOR_VERSION, details::getVndkVersionStr().c_str());
std::vector<std::string> paths = {HAL_LIBRARY_PATH_ODM, HAL_LIBRARY_PATH_VENDOR,
halLibPathVndkSp, HAL_LIBRARY_PATH_SYSTEM};
for (const std::string& path : paths) {
std::vector<std::string> libs = search(path, prefix, ".so");
for (const std::string &lib : libs) {
const std::string fullPath = path + lib;
/* 經過上面的一些添加轉換,最終
* fullPath = /vendor/lib/hw/[email protected]
* */
if (path == HAL_LIBRARY_PATH_SYSTEM) {
handle = dlopen(fullPath.c_str(), dlMode);
} else {
handle = android_load_sphal_library(fullPath.c_str(), dlMode);
}
if (handle == nullptr) {
const char* error = dlerror();
LOG(ERROR) << "Failed to dlopen " << lib << ": "
<< (error == nullptr ? "unknown error" : error);
continue;
}
/* Lambda表達式代入 */
if (!eachLib(handle, lib, sym)) {
return;
}
}
}
}
Return<sp<IBase>> get(const hidl_string& fqName,
const hidl_string& name) override {
sp<IBase> ret = nullptr;
/* [&] 此處爲Lambda表達式,簡單理解爲函數指針即可,先執行 openLibs() */
openLibs(fqName, [&](void* handle, const std::string &lib, const std::string &sym) {
/* handle :dlopen() 的返回值
* lib :[email protected]
* sym :HIDL_FETCH_ICameraProvider
*/
IBase* (*generator)(const char* name);
/* 返回 HIDL_FETCH_ICameraProvider() 函數對應的函數地址 */
*(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);
return true;
}
/* 執行 HIDL_FETCH_ICameraProvider() 函數,該函數返回CameraProvider實例對象保存在ret,
* 所以get()函數將返回 ret
* */
ret = (*generator)(name.c_str());
if (ret == nullptr) {
dlclose(handle);
return true; // this module doesn't provide this instance name
}
// Actual fqname might be a subclass.
// This assumption is tested in vts_treble_vintf_test
using ::android::hardware::details::getDescriptor;
std::string actualFqName = getDescriptor(ret.get());
CHECK(actualFqName.size() > 0);
registerReference(actualFqName, name);
return false;
});
return ret;
}
}
get() 函數傳遞進來的fpName爲 [email protected]::ICameraProvider ,name爲 legacy/0。
CameraProvider.cpp
文件路徑:android/hardware/interfaces/camera/provider/2.4/default
ICameraProvider* HIDL_FETCH_ICameraProvider(const char* name) {
/* 傳遞進來的 name 爲 legacy/0,而 kLegacyProviderName 定義爲 legacy/0 */
if (strcmp(name, kLegacyProviderName) == 0) {
/* 創建CameraProvider對象,構造函數將會調用initialize() 函數 */
CameraProvider* provider = new CameraProvider();
if (provider == nullptr) {
ALOGE("%s: cannot allocate camera provider!", __FUNCTION__);
return nullptr;
}
if (provider->isInitFailed()) {
ALOGE("%s: camera provider init failed!", __FUNCTION__);
delete provider;
return nullptr;
}
return provider;
} else if (strcmp(name, kExternalProviderName) == 0) {
ExternalCameraProvider* provider = new ExternalCameraProvider();
return provider;
}
ALOGE("%s: unknown instance name: %s", __FUNCTION__, name);
return nullptr;
}
bool CameraProvider::initialize() {
camera_module_t *rawModule;
/* 在通過 hw_get_module() 加載HAL層so:其實是通過獲取各種android屬性
* (在設備端可以通過 getprop 命令查看當前設備支持的屬性),
* 得到HAL so的名稱(*variant_keys[]),而後探測、加載該HAL so庫,並通
* 過 dlsym() 函數返回標識符爲 HAL_MODULE_INFO_SYM_AS_STR 的HMI地址
* (由於各個HAL層代碼最終會通過 HAL_MODULE_INFO_SYM 修飾,編譯器識別到
* 該符號時將會將標示地址導出爲HMI符號,從而在加載HAL so時可以獲取)
*/
int err = hw_get_module(CAMERA_HARDWARE_MODULE_ID,
(const hw_module_t **)&rawModule);
if (err < 0) {
ALOGE("Could not load camera HAL module: %d (%s)", err, strerror(-err));
return true;
}
/* rawModule 將指向 HAL 中的 camera_module_t 類型結構體,
* 此時,CameraProvider 與 camera HAL 綁定成功,可以通過
* CameraProvider操作camera HAL
*/
/* 創建 CameraModule 對象 */
/* CameraModule.cpp:android/hardware/interfaces/camera/common/1.0/default */
mModule = new CameraModule(rawModule);
/* mModule->init()主要完成以下操作:
* 1. 當camera HAL的 module_api_version >= CAMERA_MODULE_API_VERSION_2_4,將調用HAL->init()
* 2. 通過 HAL getNumberOfCameras() 獲取設置camera數量,並將該參數設置爲 mCameraInfoMap 容器的大小
* */
err = mModule->init();
if (err != OK) {
ALOGE("Could not initialize camera HAL module: %d (%s)", err, strerror(-err));
mModule.clear();
return true;
}
ALOGI("Loaded \"%s\" camera module", mModule->getModuleName());
...
mNumberOfLegacyCameras = mModule->getNumberOfCameras();
for (int i = 0; i < mNumberOfLegacyCameras; i++) {
struct camera_info info;
/* 將獲取camera信息並保存,其中將有HAL version 信息,應用
* 層將會檢查HAL層版本信息從而確認調用不同的API實現相機應用
*/
auto rc = mModule->getCameraInfo(i, &info);
if (rc != NO_ERROR) {
ALOGE("%s: Camera info query failed!", __func__);
mModule.clear();
return true;
}
...
}
return false; // mInitFailed
}
至此,已獲得CameraProvider實例對象,最終返回賦值給 registerPassthroughServiceImplementation() 函數中的 service 。
將 CameraProvider 註冊爲服務
在得到CameraProvider實例對象之後,將通過 service->registerAsService(name) 進行服務註冊。
::android::status_t ICameraProvider::registerAsService(const std::string &serviceName) {
::android::hardware::details::onRegistration("[email protected]", "ICameraProvider", serviceName);
const ::android::sp<::android::hidl::manager::V1_0::IServiceManager> sm
= ::android::hardware::defaultServiceManager();
if (sm == nullptr) {
return ::android::INVALID_OPERATION;
}
/* 通過add(),最終調用到 ServiceManagerAll.cpp
(路徑是android/out/soong/.intermediates/system/libhidl/transport/manager/1.0/
[email protected]_genc++/gen/android/hidl/manager/1.0)
中的BpHwServiceManager::add()進行註冊服務
*/
::android::hardware::Return<bool> ret = sm->add(serviceName.c_str(), this);
return ret.isOk() && ret ? ::android::OK : ::android::UNKNOWN_ERROR;
}
由於當前CameraProvider是通過hidl進行相應的操作,這部分的內容可以在網上進行搜索,這裏就不再進行相應的跟蹤了。(主要是我也不懂:-D)
最後
當CameraProvider註冊爲服務之後,CameraService運行時,將會與之進行通信進而操作camera HAL,這樣,HAL與Service進行了一道隔離。下圖爲在跟蹤代碼過程中,記錄的UML圖。
參考文章
在瞭解學習CameraProvider服務的過程中,參考了網上很多的優秀文章,感謝!