Android InputReader 输入事件处理流程

Android系统输入事件产生的底层主要是输入子系统，Android 中的输入设备有很多，例如屏幕，鼠标，键盘等都是输入设备，对于应用开发者，接触最多的也就是屏幕了。

1. 当输入设备可用时，Linux会在 /dev/input 中创建对应的设备节点。

2. 用户操作输入设备就会产生各种事件，这些事件的原始信息就会被 Linux内核中的输入子系统采集，原始信息由 Kernel space 的驱动层一直传递到设备结点。

3. InputReader读取设备节点数据并对输入事件信息进行加工处理，加工处理后的事件会交给 InputDispatcher 来处理。

以下是InputReader创建InputDevice设备、读取事件和交给InputDispatcher事件的调用流程

@frameworks/native/services/inputflinger/reader/InputReader.cpp
InputReader::start
    loopOnce()
        processEventsLocked(mEventBuffer, count);
            case EventHubInterface::DEVICE_ADDED: addDeviceLocked(rawEvent->when, rawEvent->deviceId);  //添加设备
                InputDeviceIdentifier identifier = mEventHub->getDeviceIdentifier(eventHubId);
                if(identifier.vendor == 8183 && identifier.product == 4084) { return; }  //根据keyboard设备类型判断,不添加设备，以免vd启动异常
                std::shared_ptr<InputDevice> device = createDeviceLocked(eventHubId, identifier)
@frameworks/native/services/inputflinger/reader/InputDevice.cpp                
                    device->addEventHubDevice(eventHubId);  //添加触摸光标设备
                        if (classes.test(InputDeviceClass::BATTERY) || classes.test(InputDeviceClass::LIGHT)) {  mController = std::make_unique<PeripheralController>(*contextPtr); }
                        if (classes.test(InputDeviceClass::CURSOR)) { mappers.push_back(std::make_unique<CursorInputMapper>(*contextPtr)); }
                        //addDeviceLocked Device added: id=3, eventHubId=8, name='hyn_ts', descriptor='dd768709fe8e1221a31cd1cbe2fb6da013ae6c46',sources=0x00002002
                        mDevices.insert({eventHubId, std::make_pair(std::move(contextPtr), std::move(mappers))});            
            processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
                auto deviceIt = mDevices.find(eventHubId);
                device->process(rawEvents, count);
@frameworks/native/services/inputflinger/reader/InputDevice.cpp
                    for_each_mapper_in_subdevice(rawEvent->deviceId, [rawEvent](InputMapper& mapper)
                        auto deviceIt = mDevices.find(eventHubDevice);   //eventHubDevice=8
@frameworks/native/services/inputflinger/reader/mapper/CursorInputMapper.cpp                        
                        mapper.process(rawEvent);  //CursorInputMapper::process
                            mCursorButtonAccumulator.process(rawEvent);
                            mCursorMotionAccumulator.process(rawEvent);
                            mCursorScrollAccumulator.process(rawEvent);
                                sync(rawEvent->when, rawEvent->readTime);
                                    getListener()->notifyMotion(&args);
                                        InputDispatcher::notifyMotion
                                            mPolicy->interceptMotionBeforeQueueing(args->displayId, args->eventTime, /*byref*/ policyFlags);
                                                needWake = enqueueInboundEventLocked(std::move(newEntry));
                                                    mInboundQueue.push_back(std::move(newEntry)); //放入mInboundQueue队列