前言

接上一篇Android R camera Hal启动（上）接着写，把谷歌的代码都分析完成，高通/MTK的代码就不贴了。

代码流程分析

上一篇说到getProviderImpl函数。实例化了CameraProvider对象，先看CameraProvider的构造函数。

template<typename IMPL>
struct CameraProvider : public ICameraProvider {CameraProvider() : impl() {}...
}

调用了impl也就是LegacyCameraProviderImpl_2_4的构造。

LegacyCameraProviderImpl_2_4::LegacyCameraProviderImpl_2_4() :camera_module_callbacks_t({sCameraDeviceStatusChange,sTorchModeStatusChange}) {mInitFailed = initialize();
}

camera_module_callbacks_t是HAL的回调函数，用于通知FW相机状态更新。直接看构造函数调用camera_module_callbacks_t比较奇怪，先看下LegacyCameraProviderImpl_2_4的类的申明和sCameraDeviceStatusChange/sTorchModeStatusChange两个函数的定义就能明白了。

struct LegacyCameraProviderImpl_2_4 : public camera_module_callbacks_t {...
static void sCameraDeviceStatusChange(const struct camera_module_callbacks* callbacks,int camera_id,int new_status);static void sTorchModeStatusChange(const struct camera_module_callbacks* callbacks,const char* camera_id,int new_status);...
}

LegacyCameraProviderImpl_2_4是继承了camera_module_callbacks_t，所以类构造的同时使用sCameraDeviceStatusChange/sTorchModeStatusChange初始化了camera_module_callbacks_t中的camera_device_status_change/torch_mode_status_change函数指针。
camera_module_callbacks_t结构定义如下：

typedef struct camera_module_callbacks {void (*camera_device_status_change)(const struct camera_module_callbacks*,int camera_id,int new_status);void (*torch_mode_status_change)(const struct camera_module_callbacks*,const char* camera_id,int new_status);
} camera_module_callbacks_t;

再继续往下看，调用mInitFailed = initialize();看下initialize的实现：

bool LegacyCameraProviderImpl_2_4::initialize() {camera_module_t *rawModule;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;}mModule = new CameraModule(rawModule);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());// Setup vendor tags here so HAL can setup vendor keys in camera characteristicsVendorTagDescriptor::clearGlobalVendorTagDescriptor();if (!setUpVendorTags()) {ALOGE("%s: Vendor tag setup failed, will not be available.", __FUNCTION__);}// Setup callback now because we are going to try openLegacy nexterr = mModule->setCallbacks(this);if (err != OK) {ALOGE("Could not set camera module callback: %d (%s)", err, strerror(-err));mModule.clear();return true;}mPreferredHal3MinorVersion =property_get_int32("ro.vendor.camera.wrapper.hal3TrebleMinorVersion", 3);ALOGV("Preferred HAL 3 minor version is %d", mPreferredHal3MinorVersion);switch(mPreferredHal3MinorVersion) {case 2:case 3:// OKbreak;default:ALOGW("Unknown minor camera device HAL version %d in property ""'camera.wrapper.hal3TrebleMinorVersion', defaulting to 3",mPreferredHal3MinorVersion);mPreferredHal3MinorVersion = 3;}mNumberOfLegacyCameras = mModule->getNumberOfCameras();for (int i = 0; i < mNumberOfLegacyCameras; i++) {uint32_t device_version;auto rc = mModule->getCameraDeviceVersion(i, &device_version);if (rc != NO_ERROR) {ALOGE("%s: Camera device version query failed!", __func__);mModule.clear();return true;}if (checkCameraVersion(i, device_version) != OK) {ALOGE("%s: Camera version check failed!", __func__);mModule.clear();return true;}char cameraId[kMaxCameraIdLen];snprintf(cameraId, sizeof(cameraId), "%d", i);std::string cameraIdStr(cameraId);mCameraStatusMap[cameraIdStr] = CAMERA_DEVICE_STATUS_PRESENT;addDeviceNames(i);}return false; // mInitFailed
}

先看hw_get_module函数：hardware/libhardware/hardware.c

int hw_get_module(const char *id, const struct hw_module_t **module)
{return hw_get_module_by_class(id, NULL, module);
}int hw_get_module_by_class(const char *class_id, const char *inst,const struct hw_module_t **module)
{int i = 0;char prop[PATH_MAX] = {0};char path[PATH_MAX] = {0};char name[PATH_MAX] = {0};char prop_name[PATH_MAX] = {0};if (inst)snprintf(name, PATH_MAX, "%s.%s", class_id, inst);elsestrlcpy(name, class_id, PATH_MAX);/** Here we rely on the fact that calling dlopen multiple times on* the same .so will simply increment a refcount (and not load* a new copy of the library).* We also assume that dlopen() is thread-safe.*//* First try a property specific to the class and possibly instance */snprintf(prop_name, sizeof(prop_name), "ro.hardware.%s", name);if (property_get(prop_name, prop, NULL) > 0) {if (hw_module_exists(path, sizeof(path), name, prop) == 0) {goto found;}}/* Loop through the configuration variants looking for a module */for (i=0 ; i<HAL_VARIANT_KEYS_COUNT; i++) {if (property_get(variant_keys[i], prop, NULL) == 0) {continue;}if (hw_module_exists(path, sizeof(path), name, prop) == 0) {goto found;}}/* Nothing found, try the default */if (hw_module_exists(path, sizeof(path), name, "default") == 0) {goto found;}return -ENOENT;found:/* load the module, if this fails, we're doomed, and we should not try* to load a different variant. */return load(class_id, path, module);
}

hw_get_module会调用hw_get_module_by_class去找到实现HAL的so，class_id的值就是camera。先根据ro.hardware.camera的prop来找，这是没有的，然后就是根据variant_keys的数组查找对应的prop。

static const char *variant_keys[] = {"ro.hardware",  /* This goes first so that it can pick up a differentfile on the emulator. */"ro.product.board","ro.board.platform","ro.arch"
};

高通的平台ro.hardware的值是qcom，因为这个数组中的prop的值get出来之后能找到对应的so，所以就会调用hw_module_exists拼接这个so的完整路径，如果找不到的话就会调用hw_module_exists拼接camera.default.so的全路径，camera.default.so的源码在hardware/libhardware/modules/camera/3_0目录下，平台方会自己实现camera.xxx.so，所以这里可以看成谷歌写的一个demo，如果自己想写一个camera HAL的话，可以参考着写。
再继续看hw_get_module_by_class，通过hw_module_exists拿到全路径之后，继续调用load。

static int load(const char *id,const char *path,const struct hw_module_t **pHmi)
{int status = -EINVAL;void *handle = NULL;struct hw_module_t *hmi = NULL;
#ifdef __ANDROID_VNDK__const bool try_system = false;
#elseconst bool try_system = true;
#endif/** load the symbols resolving undefined symbols before* dlopen returns. Since RTLD_GLOBAL is not or'd in with* RTLD_NOW the external symbols will not be global*/if (try_system &&strncmp(path, HAL_LIBRARY_PATH1, strlen(HAL_LIBRARY_PATH1)) == 0) {/* If the library is in system partition, no need to check* sphal namespace. Open it with dlopen.*/handle = dlopen(path, RTLD_NOW);} else {#if defined(__ANDROID_RECOVERY__)handle = dlopen(path, RTLD_NOW);
#elsehandle = android_load_sphal_library(path, RTLD_NOW);
#endif}if (handle == NULL) {char const *err_str = dlerror();ALOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");status = -EINVAL;goto done;}/* Get the address of the struct hal_module_info. */const char *sym = HAL_MODULE_INFO_SYM_AS_STR;hmi = (struct hw_module_t *)dlsym(handle, sym);if (hmi == NULL) {ALOGE("load: couldn't find symbol %s", sym);status = -EINVAL;goto done;}/* Check that the id matches */if (strcmp(id, hmi->id) != 0) {ALOGE("load: id=%s != hmi->id=%s", id, hmi->id);status = -EINVAL;goto done;}hmi->dso = handle;/* success */status = 0;done:if (status != 0) {hmi = NULL;if (handle != NULL) {dlclose(handle);handle = NULL;}} else {ALOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",id, path, hmi, handle);}*pHmi = hmi;return status;
}

load函数会根据上面传过来的地址通过dlopen打开camera.xxxx.so，这里打开的就是/vendor/lib64/hw/camera.qcom.so。然后再通过HAL_MODULE_INFO_SYM_AS_STR找到对应的符号链接。

#define HAL_MODULE_INFO_SYM_AS_STR  "HMI"

这里为什么要用HMI，自行谷歌搜索，我一开始看到这里也很懵。谷歌搜完了只知道反正就是这么定的，想要用dlsym找到对应的符号，必须要这么写：

camera_module_t HAL_MODULE_INFO_SYM __attribute__ ((visibility("default")))

再用readelf -s camera.xxxx.so可以看到符号表里面有HMI。下面是我拿手机看的符号表：

0000000000802718   344 OBJECT  GLOBAL DEFAULT   23 HMI

既然一定要有camera_module_t HAL_MODULE_INFO_SYM，那就到平台的代码里面找一下。
果然，在平台的代码里面找到了camera_module_t HAL_MODULE_INFO_SYM对应的实现。
到这里就明白了，谷歌只是注册了一个hidl服务，怎么就能调用到平台的代码完成初始化了。
再往下就是平台的具体实现，代码就不贴了，继续回头看bool LegacyCameraProviderImpl_2_4::initialize()函数。
接下来就是初始化module：

mModule = new CameraModule(rawModule);

hardware/interfaces/camera/provider/2.4/default/LegacyCameraProviderImpl_2_4.h中定义了：

using ::android::hardware::camera::common::V1_0::helper::CameraModule;

还是和前面一样，先看一下如何使用这个CameraModule的，先看一下hardware/interfaces/camera/common/1.0/default/Android.bp

cc_library_static {name: "android.hardware.camera.common@1.0-helper",vendor_available: true,defaults: ["hidl_defaults"],srcs: ["CameraModule.cpp","CameraMetadata.cpp","CameraParameters.cpp","VendorTagDescriptor.cpp","HandleImporter.cpp","Exif.cpp",],cflags: ["-Werror","-Wextra","-Wall",],shared_libs: ["liblog","libgralloctypes","libhardware","libcamera_metadata","android.hardware.graphics.mapper@2.0","android.hardware.graphics.mapper@3.0","android.hardware.graphics.mapper@4.0","libexif",],include_dirs: ["system/media/private/camera/include"],export_include_dirs: ["include"],
}

cc_library_static说明这是一个静态库，应该直接就link到android.hardware.camera.provider@2.4-impl.so里面了。找了个手机看来一下，果然搜不到这个库，再看一下android.hardware.camera.provider@2.4-impl的编译文件。

cc_library_shared {name: "android.hardware.camera.provider@2.4-impl",...static_libs: ["android.hardware.camera.common@1.0-helper",],...
}

再看CameraModule的构造：

CameraModule::CameraModule(camera_module_t *module) : mNumberOfCameras(0) {if (module == NULL) {ALOGE("%s: camera hardware module must not be null", __FUNCTION__);assert(0);}mModule = module;
}

因为CameraModule就是相机HAL的一个封装，所以初始化就是要保存camera_module_t到mModule。再继续看initialize函数。调用了err = mModule->init();这个实际上就是camera_module_t的init，平台的代码中实现了init，谷歌原生代码并没有实现这部分。再往下就没有什么特殊的代码就是一些初始化，获取属性，最终将camera状态设置成CAMERA_DEVICE_STATUS_PRESENT。initialize函数初始化完成，返回值是false。。。最终这个值给到mInitFailed。
这里的代码看完，再回到hardware/interfaces/camera/provider/2.4/default/CameraProvider_2_4.cpp中，provider初始化完成，调用provider->isInitFailed()检查是不是init成功。

总结

到这里就全部结束了，上面的流程是按照看代码的过程写的，有点乱，好多细节也没有说，不过也算是梳理了整个代码流程。最主要是说明HAL进程如何加载平台so并且关联到平台代码的。

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Android R camera Hal启动（下）

文章目录

前言

代码流程分析

总结

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