Android Camera原理之camera provider啓動

1.camera provider進程介紹：

cameraserver 736 1 274664 69564 binder_thread_read f3de10cc S android.hardware.camera.provider@2.4-service

 

其中的pid是736，說明camera provider進程啓動的時機比較早，並且權限組是 cameraserver

手機上運行的android.hardware.camera.provider@2.4-service進程是支持camera運行的重要進程。

camera架構.jpg

 

上面這張圖比較清楚的表現了camera provider進程在camera架構中位置，做爲承上啓下的部分，和cameraserver進程和底層的驅動交互，camera provider進程很是重要，camera HAL層幾乎所有運行在camera provider進程中完成。

android.hardware.camera.provider@2.4-service在手機啓動的時候就會啓動起來，下面總體分析一下android.hardware.camera.provider@2.4-service進程的啓動過程。

2.camera provider進程啓動流程：

首先看下camera provider所在源碼中的位置：hardware/interfaces/camera/provider/

cameraprovider代碼目錄.jpg

能夠看出來在hardware/interfaces/camera/provider/2.4/default/ 下面有幾個rc文件，Android初始化就是執行這些rc文件，這裏執行的是android.hardware.camera.provider@2.4-service.rc文件，看看其中的執行代碼。

 

service vendor.camera-provider-2-4 /vendor/bin/hw/android.hardware.camera.provider@2.4-service
    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

第一行就看到了啓動一個 /vendor/bin/hw/android.hardware.camera.provider@2.4-service 進程。

下面列出camera provider進程的啓動流程，你們能夠先看一下。

camera provider進程啓動流程.jpg

 

service.cpp : hardware/interfaces/camera/provider/2.4/default/service.cpp

CameraProvider : hardware/interfaces/camera/provider/2.4/default/CameraProvider.cpp

hardware.c : hardware/libhardware/hardware.c

CameraModule : hardware/interfaces/camera/common/1.0/default/CameraModule.cpp

QCamera2Factory : hardware/qcom/camera/QCamera2Factory.cpp

QCameraFlash : hardware/qcom/camera/QCamera2/util/QCameraFlash.cpp

QCamera3HardwareInterface : hardware/qcom/camera/QCamera2/HAL3/QCamera3HWI.cpp

這兒值得講一講的就是native中的函數指針的問題，從camera interfaces中將函數指針映射到camera hal層中。
主要從CameraModule中調用到QCamera2Factory中。期間使用了camera_module_t這個結構體。能夠看下 CameraModule::init函數。

int CameraModule::init() {
    ATRACE_CALL();
    int res = OK;
    if (getModuleApiVersion() >= CAMERA_MODULE_API_VERSION_2_4 &&
            mModule->init != NULL) {
        ATRACE_BEGIN("camera_module->init");
        res = mModule->init();
        ATRACE_END();
    }
    mCameraInfoMap.setCapacity(getNumberOfCameras());
    return res;
}

這兒調用的mModule->init(); 這個mModule就是camera_module_t結構體對象，這時候翻看一下《Android Camera原理之camera HAL底層數據結構與類總結》

typedef struct camera_module {
    hw_module_t common;
    int (*get_number_of_cameras)(void);
    int (*get_camera_info)(int camera_id, struct camera_info *info);
    int (*set_callbacks)(const camera_module_callbacks_t *callbacks);
    void (*get_vendor_tag_ops)(vendor_tag_ops_t* ops);
    int (*open_legacy)(const struct hw_module_t* module, const char* id,
            uint32_t halVersion, struct hw_device_t** device);
    int (*set_torch_mode)(const char* camera_id, bool enabled);
    int (*init)();
    void* reserved[5];
} camera_module_t;

結構體中有一些函數指針，咱們如今須要搞清楚這些函數指針被映射到什麼地方了？
hardware中interface中提供了原生的映射方法，在hardware/libhardware/modules/camera/3_0/CameraHAL.cpp中。

camera_module_t HAL_MODULE_INFO_SYM __attribute__ ((visibility("default"))) = {
    .common = {
        .tag                = HARDWARE_MODULE_TAG,
        .module_api_version = CAMERA_MODULE_API_VERSION_2_2,
        .hal_api_version    = HARDWARE_HAL_API_VERSION,
        .id                 = CAMERA_HARDWARE_MODULE_ID,
        .name               = "Default Camera HAL",
        .author             = "The Android Open Source Project",
        .methods            = &gCameraModuleMethods,
        .dso                = NULL,
        .reserved           = {0},
    },
    .get_number_of_cameras = get_number_of_cameras,
    .get_camera_info       = get_camera_info,
    .set_callbacks         = set_callbacks,
    .get_vendor_tag_ops    = get_vendor_tag_ops,
    .open_legacy           = NULL,
    .set_torch_mode        = NULL,
    .init                  = NULL,
    .reserved              = {0},
};

這是通用的映射，咱們手機的芯片會從新這個HAL層接口，例如使用高通芯片的話，會在hardware/qcom/camera/QCamera2/QCamera2Hal.cpp中重寫這個函數映射。
實際上可能不是這個路徑，根據你本地實際的hal層從新方法來查找這些函數映射。

static hw_module_t camera_common = {
    .tag                    = HARDWARE_MODULE_TAG,
    .module_api_version     = CAMERA_MODULE_API_VERSION_2_4,
    .hal_api_version        = HARDWARE_HAL_API_VERSION,
    .id                     = CAMERA_HARDWARE_MODULE_ID,
    .name                   = "QCamera Module",
    .author                 = "Qualcomm Innovation Center Inc",
    .methods                = &qcamera::QCamera2Factory::mModuleMethods,
    .dso                    = NULL,
    .reserved               = {0}
};

camera_module_t HAL_MODULE_INFO_SYM = {
    .common                 = camera_common,
    .get_number_of_cameras  = qcamera::QCamera2Factory::get_number_of_cameras,
    .get_camera_info        = qcamera::QCamera2Factory::get_camera_info,
    .set_callbacks          = qcamera::QCamera2Factory::set_callbacks,
    .get_vendor_tag_ops     = qcamera::QCamera3VendorTags::get_vendor_tag_ops,
    .open_legacy            = NULL,
    .set_torch_mode         = qcamera::QCamera2Factory::set_torch_mode,
    .init                   = NULL,
    .reserved               = {0}
};

明確這些函數映射以後，接下來能夠直接調用到hal層了。再底層就是芯片中複寫的核心方法了，暫時不做深刻介紹了。