Android4.2.2 CameraService服务启动和应用端camera初始化记录

 本文均属自己阅读源码的点滴总结，转账请注明出处谢谢。
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Android源码版本Version：4.2.2; 硬件平台 全志A31
 
 
之前的10篇博文主要是记录了Android4.2.2的SurfaceFlinger的相关内容，为何之前会投入那么多的时间，原因就在于之前在看camera的架构时，遇到了本地的ANativeWindow和Surface的内容。而这些是SurfaceFlinger中最常见的应用端的使用品。故而在学习完了SurfaceFlinger之后就来看看Camera的的架构内容。这里先和大家分享android4.2.2的CameraService的启动过程与其的架构。

1.cameraService在何处启动
mediaserver启动了我们cameraservice，即所谓的多媒体相关的服务总管。int main(int argc, char** argv)
{
signal(SIGPIPE, SIG_IGN);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate();//多媒体服务的启动包括音频，摄像头等
MediaPlayerService::instantiate();
CameraService::instantiate();
AudioPolicyService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
之前的文章有提到过一般的Service的启动方式，这里是典型的一种BinderService的启动class BinderService
{
public:
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
}

static void publishAndJoinThreadPool(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}

static void instantiate() { publish(); }//两种初始化binder服务的方式

static status_t shutdown() {
return NO_ERROR;
}
}; CameraService::CameraService()
:mSoundRef(0), mModule(0)
{
ALOGI("CameraService started (pid=%d)", getpid());
gCameraService = this;
}

void CameraService::onFirstRef()//camerservice生成sp后被调用
{
BnCameraService::onFirstRef();

if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,
(const hw_module_t **)&mModule) < 0) {//获取并加载mModule变量，实际的hal层的硬件库camera.fiber.so，加载了模块
ALOGE("Could not load camera HAL module");
mNumberOfCameras = 0;
}
else {
mNumberOfCameras = mModule->get_number_of_cameras();//通过hal获取camera的数目
if (mNumberOfCameras > MAX_CAMERAS) {
ALOGE("Number of cameras(%d) > MAX_CAMERAS(%d).",
mNumberOfCameras, MAX_CAMERAS);
mNumberOfCameras = MAX_CAMERAS;
}
for (int i = 0; i < mNumberOfCameras; i++) {
setCameraFree(i);
}
}
}
调用CameraService的构造函数后，会自动执行onFirstRef().在该函数内部主要实现了对Camera的Hal层的操作。
通过hw_get_module()获得加载HAL层的模块句柄到mModule成员变量之中，并获得硬件的Camera的个数到mNumberOfCameras之中。可以看到CameraService比起SurfaceFinger这个强大的service来说简单了很多。

step3，camera客户端的建立
通java层的new Camera()来到JNI层，依次经过camera.java再到本地JNI的android_hardware_Camera.cpp。
camera.java中Camera.open()函数的执行 public static Camera open(int cameraId) {
return new Camera(cameraId);
}

/**
* Creates a new Camera object to access the first back-facing camera on the
* device. If the device does not have a back-facing camera, this returns
* null.
* @see #open(int)
*/
public static Camera open() {
int numberOfCameras = getNumberOfCameras();
CameraInfo cameraInfo = new CameraInfo();
for (int i = 0; i < numberOfCameras; i++) {
getCameraInfo(i, cameraInfo);
if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
return new Camera(i);
}
}
return null;
}
Camera中的类 Camera(int cameraId) {
mShutterCallback = null;
mRawImageCallback = null;
mJpegCallback = null;
mPreviewCallback = null;
mPostviewCallback = null;
mZoomListener = null;

Looper looper;
if ((looper = Looper.myLooper()) != null) {
.....
native_setup(new WeakReference<Camera>(this), cameraId);
}
JNI层的android_hardware_camera.cpp中：// connect to camera service
static void android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
jobject weak_this, jint cameraId)
{
sp<Camera> camera = Camera::connect(cameraId);//调用Camera的connect函数

if (camera == NULL) {
jniThrowRuntimeException(env, "Fail to connect to camera service");
return;
}

// make sure camera hardware is alive
if (camera->getStatus() != NO_ERROR) {
jniThrowRuntimeException(env, "Camera initialization failed");
return;
}

jclass clazz = env->GetObjectClass(thiz);
if (clazz == NULL) {
jniThrowRuntimeException(env, "Can't find android/hardware/Camera");
return;
}
......
}来到Camera应用层的类connect函数，目标是请求CameraService新建一个Camera客户端。

step4：camera客户端的connect函数sp<Camera> Camera::connect(int cameraId)
{
ALOGV("connect");
sp<Camera> c = new Camera();//BnCameraClient
const sp<ICameraService>& cs = getCameraService();//获取一个Bpcamerservice
if (cs != 0) {
c->mCamera = cs->connect(c, cameraId);//基于binder驱动最终会去调用camerservice侧的connect,mCamera指向一个Bpcamera
}
if (c->mCamera != 0) {
c->mCamera->asBinder()->linkToDeath(c);
c->mStatus = NO_ERROR;
} else {
c.clear();
}
return c;
}
新建一个应用端的Camera，该类class Camera : public BnCameraClient, public IBinder::DeathRecipient继承关系如下。

cs = getCameraService()通过SM获取CameraService在本地的一个代理。调用connect函数后最终调用CameraService侧的connect()函数。 virtual sp<ICamera> connect(const sp<ICameraClient>& cameraClient, int cameraId)
{
Parcel data, reply;
data.writeInterfaceToken(ICameraService::getInterfaceDescriptor());
data.writeStrongBinder(cameraClient->asBinder());
data.writeInt32(cameraId);//发送到服务端的数据包
remote()->transact(BnCameraService::CONNECT, data, &reply);//实际调用的是Bpbinder的transact
return interface_cast<ICamera>(reply.readStrongBinder());//传入Bpbinder的handle数值返回一个new BpCamera,实际是服务端的Bncamera
}
};在这里可以看到这边传入一个本地Camera类对象即new Camera()，这个匿名的binder对象将通过Binder驱动传递给CameraService。主要用于后续CameraService的回调给应用层的Camera来处理

step5:CameraSevice端的connect函数sp<ICamera> CameraService::connect(
const sp<ICameraClient>& cameraClient, int cameraId) {
int callingPid = getCallingPid();

LOG1("CameraService::connect E (pid %d, id %d)", callingPid, cameraId);

if (!mModule) {
ALOGE("Camera HAL module not loaded");
return NULL;
}

sp<Client> client;
if (cameraId < 0 || cameraId >= mNumberOfCameras) {
ALOGE("CameraService::connect X (pid %d) rejected (invalid cameraId %d).",
callingPid, cameraId);
return NULL;
}

char value[PROPERTY_VALUE_MAX];
property_get("sys.secpolicy.camera.disabled", value, "0");
if (strcmp(value, "1") == 0) {
// Camera is disabled by DevicePolicyManager.
ALOGI("Camera is disabled. connect X (pid %d) rejected", callingPid);
return NULL;
}

Mutex::Autolock lock(mServiceLock);
if (mClient[cameraId] != 0) {
client = mClient[cameraId].promote();
if (client != 0) {
if (cameraClient->asBinder() == client->getCameraClient()->asBinder()) {
LOG1("CameraService::connect X (pid %d) (the same client)",
callingPid);
return client;
} else {
ALOGW("CameraService::connect X (pid %d) rejected (existing client).",
callingPid);
return NULL;
}
}
mClient[cameraId].clear();
}

if (mBusy[cameraId]) {
ALOGW("CameraService::connect X (pid %d) rejected"
" (camera %d is still busy).", callingPid, cameraId);
return NULL;
}

struct camera_info info;
if (mModule->get_camera_info(cameraId, &info) != OK) {//获取camera的相关信息
ALOGE("Invalid camera id %d", cameraId);
return NULL;
}

int deviceVersion;
if (mModule->common.module_api_version == CAMERA_MODULE_API_VERSION_2_0) {
deviceVersion = info.device_version;
} else {
deviceVersion = CAMERA_DEVICE_API_VERSION_1_0;
}

switch(deviceVersion) {
case CAMERA_DEVICE_API_VERSION_1_0:
client = new CameraClient(this, cameraClient, cameraId,
info.facing, callingPid, getpid());//client是CameraClient的基类，新建一个camerservice侧的cameraclient
break;
case CAMERA_DEVICE_API_VERSION_2_0:
client = new Camera2Client(this, cameraClient, cameraId,
info.facing, callingPid, getpid());
break;
default:
ALOGE("Unknown camera device HAL version: %d", deviceVersion);
return NULL;
}

if (client->initialize(mModule) != OK) {//cameraclient init初始化，实际调用的是CameraClient
return NULL;
}

cameraClient->asBinder()->linkToDeath(this);

mClient[cameraId] = client;//连接请求后新建立的
LOG1("CameraService::connect X (id %d, this pid is %d)", cameraId, getpid());
return client;//返回CameraClient
}
分以下几个过程来分析这个函数：
a. sp<Client> client;一个CameraService内部的客户端类
先查看当前服务端维护的camera client个数mClient[cameraId] != 0，初次启动是该数为0.

b.获取底层camera模块的信息get_camera_info，查看当前的api版本信息是CAMERA_MODULE_API_VERSION_2_0还是CAMERA_MODULE_API_VERSION_1_0.我的平台是1.0故执行如下： switch(deviceVersion) {
case CAMERA_DEVICE_API_VERSION_1_0:
client = new CameraClient(this, cameraClient, cameraId,
info.facing, callingPid, getpid());//client是CameraClient的基类，新建一个camerservice侧的cameraclient
break;
c.CameraClient的建立，该类继承了public CameraService::Client这个CameraService的内部类，Client继承了BnCamera。

d.client->initialize(mModule)的处理，和硬件相关status_t CameraClient::initialize(camera_module_t *module) {//一个cameraClient新建一个CameraHardwareInterface硬接口
int callingPid = getCallingPid();
LOG1("CameraClient::initialize E (pid %d, id %d)", callingPid, mCameraId);

char camera_device_name[10];
status_t res;
snprintf(camera_device_name, sizeof(camera_device_name), "%d", mCameraId);

mHardware = new CameraHardwareInterface(camera_device_name);//新建一个camera硬件接口，camera_device_name为设备名
res = mHardware->initialize(&module->common);//直接底层硬件的初始
if (res != OK) {
ALOGE("%s: Camera %d: unable to initialize device: %s (%d)",
__FUNCTION__, mCameraId, strerror(-res), res);
mHardware.clear();
return NO_INIT;
}

mHardware->setCallbacks(notifyCallback,
dataCallback,
dataCallbackTimestamp,
(void *)mCameraId);//将camerservice处的回调函数注册到HAL处

// Enable zoom, error, focus, and metadata messages by default
enableMsgType(CAMERA_MSG_ERROR | CAMERA_MSG_ZOOM | CAMERA_MSG_FOCUS |
CAMERA_MSG_PREVIEW_METADATA | CAMERA_MSG_FOCUS_MOVE |
CAMERA_MSG_CONTINUOUSSNAP | CAMERA_MSG_SNAP | CAMERA_MSG_SNAP_THUMB |
CAMERA_MSG_SNAP_FD); //enable the continuoussnap and singlesnap message by fuqiang

LOG1("CameraClient::initialize X (pid %d, id %d)", callingPid, mCameraId);
return OK;
}这里出现了一个封装Camera底层操作的一个硬件接口类CameraHardwareInterface，可以屏蔽不同的平台硬件特性，主要是实现的HAL的相关操作。

step6.CameraHardwareInterface接口类的实现initialize()函数。 status_t initialize(hw_module_t *module)
{
ALOGI("Opening camera %s", mName.string());
int rc = module->methods->open(module, mName.string(),
(hw_device_t **)&mDevice);//这里打开camera硬件设备
if (rc != OK) {
ALOGE("Could not open camera %s: %d", mName.string(), rc);
return rc;
}
initHalPreviewWindow();//初始preview的相关流opspreview_stream_ops，初始化hal的预览窗口
return rc;
}
这里的module就是底层的camera模块，最终完成open的操作，这里占时不说明HAL的操作，后续会专门分享camera的HAL的实现。

step7:setCallbacks()设置回调函数，即注册回调函数到HAL处 void setCallbacks(notify_callback notify_cb,
data_callback data_cb,
data_callback_timestamp data_cb_timestamp,
void* user)
{
mNotifyCb = notify_cb;
mDataCb = data_cb;
mDataCbTimestamp = data_cb_timestamp;
mCbUser = user;

ALOGV("%s(%s)", __FUNCTION__, mName.string());

if (mDevice->ops->set_callbacks) {
mDevice->ops->set_callbacks(mDevice,
__notify_cb,
__data_cb,
__data_cb_timestamp,
__get_memory,
this);//传入的是__notify_cb函数
}//硬件设备设置回调
}
分别消息回调，数据回调，时间戳回调，以及内存相关操作的回调。

step8:
mClient[cameraId] = client将新建好的cameraclient对象维护到CameraService中并返回退出connect，而最终通过Binder驱动返回到客户端的是CameraClient的代理BpCameraClient，是一个匿名的Binder服务。
c->mCamera = cs->connect(c, cameraId);将这个服务端的cameraclient维护到本地应用端的Camera的mCamera成员中。而后续的Camera的相关操作都通过该mCamera成员和CameraService进行进一步的交互操作。

camera的一个调用架构图：