打开相机流程中，从 APP 到 CameraService 再到 HAL Service 的连路创建流程都已经简略分析了一遍。现在需要分析最后的阶段，即从 HAL Service 连接到 Camera HAL 的部分
在 HAL3 中，Camera HAL 的接口转化层（以及流解析层）由 QCamera3HardwareInterface 担当，而接口层与实现层与 HAL1 中基本没什么差别，都是在 mm_camera_interface.c 与 mm_camera.c 中。
那么接口转化层的实例是何时创建的，又是怎么初始化的，创建它的时候，与接口层、实现层又有什么交互？通过下图展示的主要调用流程可以简单了解了解。
接下来可以看看代码流程。
HAL Service
CameraModule
文件路径：hardware\interfaces\camera\common\1.0\default\CameraModule.cpp
上回说到，CameraDevice::open 的实现中，调用了 mModule->open，即 CameraModule::open。来看看它的具体实现
int CameraModule::open(const char* id, struct hw_device_t** device) {
int res;
ATRACE_BEGIN("camera_module->open");
res = filterOpenErrorCode(mModule->common.methods->open(&mModule->common, id, device));
ATRACE_END();
return res;
}
通过代码来看，它做的事并不多，主要是调用 mModule->common.methods->open，来进入下一层级的流程。
而这里则需要注意了，open 是一个函数指针，它指向的是 QCamera2Factory 的 camera_device_open 方法，至于为什么和 QCamera2Factory 有关，这就要回头看 HAL Service 的启动初始化流程了。对我来说这不重要，就不赘述了
文件路径：hardware\qcom\camera\qcamera2\QCamera2Factory.cpp
/*===========================================================================
* FUNCTION : camera_device_open
*
* DESCRIPTION: static function to open a camera device by its ID
*
* PARAMETERS :
* @camera_id : camera ID
* @hw_device : ptr to struct storing camera hardware device info
*
* RETURN : int32_t type of status
* NO_ERROR -- success
* none-zero failure code
*==========================================================================*/
int QCamera2Factory::camera_device_open(
const struct hw_module_t *module, const char *id,
struct hw_device_t **hw_device)
{
int rc = NO_ERROR;
if (module != &HAL_MODULE_INFO_SYM.common) {
LOGE("Invalid module. Trying to open %p, expect %p",
module, &HAL_MODULE_INFO_SYM.common);
return INVALID_OPERATION;
}
if (!id) {
LOGE("Invalid camera id");
return BAD_VALUE;
}
#ifdef QCAMERA_HAL1_SUPPORT
if(gQCameraMuxer)
rc = gQCameraMuxer->camera_device_open(module, id, hw_device);
else
#endif
rc = gQCamera2Factory->cameraDeviceOpen(atoi(id), hw_device);
return rc;
}
struct hw_module_methods_t QCamera2Factory::mModuleMethods = {
.open = QCamera2Factory::camera_device_open,
};
往下看cameraDeviceOpen方法
首先创建了 QCamera3HardwareInterface 的实例。
调用实例的 openCamera 方法。
/*===========================================================================
* FUNCTION : cameraDeviceOpen
*
* DESCRIPTION: open a camera device with its ID
*
* PARAMETERS :
* @camera_id : camera ID
* @hw_device : ptr to struct storing camera hardware device info
*
* RETURN : int32_t type of status
* NO_ERROR -- success
* none-zero failure code
*==========================================================================*/
int QCamera2Factory::cameraDeviceOpen(int camera_id,
struct hw_device_t **hw_device)
{
int rc = NO_ERROR;
if (camera_id < 0 || camera_id >= mNumOfCameras)
return -ENODEV;
if ( NULL == mHalDescriptors ) {
LOGE("Hal descriptor table is not initialized!");
return NO_INIT;
}
LOGI("Open camera id %d API version %d",
camera_id, mHalDescriptors[camera_id].device_version);
if ( mHalDescriptors[camera_id].device_version == CAMERA_DEVICE_API_VERSION_3_0 ) {
CAMSCOPE_INIT(CAMSCOPE_SECTION_HAL);
QCamera3HardwareInterface *hw = new QCamera3HardwareInterface(mHalDescriptors[camera_id].cameraId,
mCallbacks);
if (!hw) {
LOGE("Allocation of hardware interface failed");
return NO_MEMORY;
}
rc = hw->openCamera(hw_device);
if (rc != 0) {
delete hw;
}
}
#ifdef QCAMERA_HAL1_SUPPORT
else if (mHalDescriptors[camera_id].device_version == CAMERA_DEVICE_API_VERSION_1_0) {
QCamera2HardwareInterface *hw = new QCamera2HardwareInterface((uint32_t)camera_id);
if (!hw) {
LOGE("Allocation of hardware interface failed");
return NO_MEMORY;
}
rc = hw->openCamera(hw_device);
if (rc != NO_ERROR) {
delete hw;
}
}
#endif
else {
LOGE("Device version for camera id %d invalid %d",
camera_id,
mHalDescriptors[camera_id].device_version);
return BAD_VALUE;
}
return rc;
}
往下看，
文件路径：hardware\qcom\camera\qcamera2\hal3\QCamera3HWI.cpp
首先需要注意的是内部成员 mCameraOps 的定义。
在构造实例时，有 mCameraDevice.ops = &mCameraOps;，这点需要记住。
camera3_device_ops_t QCamera3HardwareInterface::mCameraOps = {
.initialize = QCamera3HardwareInterface::initialize,
.configure_streams = QCamera3HardwareInterface::configure_streams,
.register_stream_buffers = NULL,
.construct_default_request_settings = QCamera3HardwareInterface::construct_default_request_settings,
.process_capture_request = QCamera3HardwareInterface::process_capture_request,
.get_metadata_vendor_tag_ops = NULL,
.dump = QCamera3HardwareInterface::dump,
.flush = QCamera3HardwareInterface::flush,
.reserved = {0},
};
