camera进程通信分析

1.AIDL
用于 APP 和 cameraservice 端交互的

https://android.googlesource.com/platform/frameworks/av/+/refs/tags/android-9.0.0_r55/camera/aidl/android/hardware

编译后的路径在

out/soong/.intermediates/frameworks/av/camera/libcamera_client/android_arm64_armv8-a_cortex-a53_core_shared/gen/aidl/

cameraservice端的代码在frameworks/av/services/camera/libcameraservice/下面

2.HIDL
用于cameraservice 和 camerahal 端交互的

https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/provider/2.4/
ICameraProvider.hal
ICameraProviderCallback.hal
https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/device/3.2/
ICameraDevice.hal
ICameraDeviceCallback.hal
ICameraDeviceSession.hal

编译后的路径在

out/soong/.intermediates/frameworks/hardware/interfaces/camera/device/3.2/android.hardware.camera.device@3.2_genc++/gen/android.hardware/camera/device/3.2/

下面分析一下open的操作
/services/camera/libcameraservice/common/CameraProviderManager.cpp

status_t CameraProviderManager::openSession(const std::string &id,
        const sp<hardware::camera::device::V3_2::ICameraDeviceCallback>& callback,
        /*out*/
        sp<hardware::camera::device::V3_2::ICameraDeviceSession> *session) {
 
    std::lock_guard<std::mutex> lock(mInterfaceMutex);
 
    auto deviceInfo = findDeviceInfoLocked(id,
            /*minVersion*/ {3,0}, /*maxVersion*/ {4,0});
    if (deviceInfo == nullptr) return NAME_NOT_FOUND;
 
    auto *deviceInfo3 = static_cast<ProviderInfo::DeviceInfo3*>(deviceInfo);
 
    Status status;
    hardware::Return<void> ret;
    ret = deviceInfo3->mInterface->open(callback, [&status, &session]
            (Status s, const sp<device::V3_2::ICameraDeviceSession>& cameraSession) {
                status = s;
                if (status == Status::OK) {
                    *session = cameraSession;
                }
            });
    if (!ret.isOk()) {
        ALOGE("%s: Transaction error opening a session for camera device %s: %s",
                __FUNCTION__, id.c_str(), ret.description().c_str());
        return DEAD_OBJECT;
    }
    return mapToStatusT(status);
}

可以 参考如下链接：Android8.0相机源码深入解析(四)
这个open 最终会调用的是
camera/device/3.2/ICameraDevice.hal

    /**
     * open:
     *
     * Power on and initialize this camera device for active use, returning a
     * session handle for active operations.
     *
     * @param callback Interface to invoke by the HAL for device asynchronous
     *     events. For HALs newer than version 3.2, HAL must use castFrom
     *     method to check the exact version of callback sent by camera service.
     *
     * @return status Status code for the operation, one of:
     *     OK:
     *         On a successful open of the camera device.
     *     INTERNAL_ERROR:
     *         The camera device cannot be opened due to an internal
     *         error.
     *     ILLEGAL_ARGUMENT:
     *         The callbacks handle is invalid (for example, it is null).
     *     CAMERA_IN_USE:
     *         This camera device is already open.
     *     MAX_CAMERAS_IN_USE:
     *         The maximal number of camera devices that can be
     *         opened concurrently were opened already.
     *     CAMERA_DISCONNECTED:
     *         This external camera device has been disconnected, and is no
     *         longer available. This interface is now stale, and a new instance
     *         must be acquired if the device is reconnected. All subsequent
     *         calls on this interface must return CAMERA_DISCONNECTED.
     * @return session The interface to the newly-opened camera session,
     *     or null if status is not OK.
     */
    open(ICameraDeviceCallback callback) generates
            (Status status, ICameraDeviceSession session);

可以发现 ICameraDevice 又在HAL被实现，Framework -> HAL 进程间通信就这样实现操作完成了