InputManagerService的InputReader机制

文章参考：http://gityuan.com/2016/12/11/input-reader/

概述

介绍IMS服务的启动过程会创建两个native线程，分别是InputReader,InputDispatcher. 接下来从InputReader线程的执行过程从threadLoop为起点开始分析。

InputManager::start

status_t InputManager::start() {
    // 启动InputDispatcher的事件分发
    status_t result = mDispatcher->start();
    if (result) {
        ALOGE("Could not start InputDispatcher thread due to error %d.", result);
        return result;
    }
    // 启动InputReader
    result = mReader->start();
    if (result) {
        ALOGE("Could not start InputReader due to error %d.", result);

        mDispatcher->stop();
        return result;
    }

    return OK;
}

InputDispatcher::start

status_t InputDispatcher::start() {
    if (mThread) {
        return ALREADY_EXISTS;
    }
    // 启动一个InputDispatcher线程
    mThread = std::make_unique<InputThread>(
            "InputDispatcher", [this]() { dispatchOnce(); }, [this]() { mLooper->wake(); });
    return OK;
}

InputReader::start

/**
 * 代码位于：framework/native/services/inputflinger/reader/InputReader.cpp
 **/
status_t InputReader::start() {
    if (mThread) {
        return ALREADY_EXISTS;
    }
    // 启动一个InputReader线程
    // 循环调用loopOnce()。整个过程是不断循环的地调用InputReader的loopOnce()方法
    // make_unique的智能指针需要学习
    mThread = std::make_unique<InputThread>(
            "InputReader", [this]() { loopOnce(); }, [this]() { mEventHub->wake(); });
    return OK;
}

InputManager的start方法的主要功能是启动两个线程:

• 启动线程“InputReader”
• 启动线程”InputDispatcher“

那么，下面我们看一下InputReader的线程的业务逻辑。InputReader的线程中，回会调用到loopOnce()方法。

InputReader::loopOnce()

/**
 * 代码位于：framework/native/services/inputflinger/reader/InputReader.cpp
 **/
status_t InputReader::start() {
    if (mThread) {
        return ALREADY_EXISTS;
    }
    // 启动一个InputReader线程
    // 循环调用loopOnce()。整个过程是不断循环的地调用InputReader的loopOnce()方法
    // make_unique的智能指针需要学习
    mThread = std::make_unique<InputThread>(
            "InputReader", [this]() { loopOnce(); }, [this]() { mEventHub->wake(); });
    return OK;
}

status_t InputReader::stop() {
    if (mThread && mThread->isCallingThread()) {
        ALOGE("InputReader cannot be stopped from its own thread!");
        return INVALID_OPERATION;
    }
    mThread.reset();
    return OK;
}
/**
 * 代码位于：framework/native/services/inputflinger/reader/InputReader.cpp
 **/
void InputReader::loopOnce() {
    int32_t oldGeneration;
    int32_t timeoutMillis;
    bool inputDevicesChanged = false;
    std::vector<InputDeviceInfo> inputDevices;
    { // acquire lock
        AutoMutex _l(mLock);

        oldGeneration = mGeneration;
        timeoutMillis = -1;

        uint32_t changes = mConfigurationChangesToRefresh;
        if (changes) {
            mConfigurationChangesToRefresh = 0;
            timeoutMillis = 0;
            refreshConfigurationLocked(changes);
        } else if (mNextTimeout != LLONG_MAX) {
            nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
            timeoutMillis = toMillisecondTimeoutDelay(now, mNextTimeout);
        }
    } // release lock
    // 从EventHub读取事件，其中EVENT_BUFFER_SIZE = 256
    size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);

    { // acquire lock
        // 获取同步锁
        AutoMutex _l(mLock);
        mReaderIsAliveCondition.broadcast();
        // 处理事件
        if (count) {
            processEventsLocked(mEventBuffer, count);
        }
        if (mNextTimeout != LLONG_MAX) {
            nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
            if (now >= mNextTimeout) {
#if DEBUG_RAW_EVENTS
                ALOGD("Timeout expired, latency=%0.3fms", (now - mNextTimeout) * 0.000001f);
#endif
                mNextTimeout = LLONG_MAX;
                timeoutExpiredLocked(now);
            }
        }

        if (oldGeneration != mGeneration) {
            inputDevicesChanged = true;
            getInputDevicesLocked(inputDevices);
        }
    } // release lock

    // Send out a message that the describes the changed input devices.
    // 如果输入设备发生改变。则发送通知告知输入设备发生改变
    if (inputDevicesChanged) {
        mPolicy->notifyInputDevicesChanged(inputDevices);
    }

    // Flush queued events out to the listener.
    // This must happen outside of the lock because the listener could potentially call
    // back into the InputReader's methods, such as getScanCodeState, or become blocked
    // on another thread similarly waiting to acquire the InputReader lock thereby
    // resulting in a deadlock.  This situation is actually quite plausible because the
    // listener is actually the input dispatcher, which calls into the window manager,
    // which occasionally calls into the input reader.
    // 通过监听回调。发送事件到InputDispatcher
    mQueuedListener->flush();
}

我们可以看到。InputReader会通过会不断地循环调用loopOnce()。源源不断的从EventHub中获取输入事件。下面，我们就来看一下比较重要的EventHub是怎么获取输入事件的。

EventHub->getEvents

/**
 * frameworks/native/services/inputflinger/reader/EventHub.cpp
 **/
size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
    // 确认缓存数据区空间大于1
    ALOG_ASSERT(bufferSize >= 1);
    // 加锁处理
    std::scoped_lock _l(mLock);

    struct input_event readBuffer[bufferSize];
    // 定义原始事件
    RawEvent* event = buffer;
    // 传入的缓冲区的大小，一般为256
    size_t capacity = bufferSize;
    bool awoken = false;
    for (;;) {
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);

        // Reopen input devices if needed.
        if (mNeedToReopenDevices) {
            mNeedToReopenDevices = false;

            ALOGI("Reopening all input devices due to a configuration change.");

            closeAllDevicesLocked();
            mNeedToScanDevices = true;
            break; // return to the caller before we actually rescan
        }

        // Report any devices that had last been added/removed.
        for (auto it = mClosingDevices.begin(); it != mClosingDevices.end();) {
            std::unique_ptr<Device> device = std::move(*it);
            ALOGV("Reporting device closed: id=%d, name=%s\n", device->id, device->path.c_str());
            event->when = now;
            event->deviceId = (device->id == mBuiltInKeyboardId)
                    ? ReservedInputDeviceId::BUILT_IN_KEYBOARD_ID
                    : device->id;
            event->type = DEVICE_REMOVED;
            event += 1;
            it = mClosingDevices.erase(it);
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }
        // 进行输入事件的设备扫描
        if (mNeedToScanDevices) {
            mNeedToScanDevices = false;
            // TODO 具体扫描设备的逻辑，我们后来再看
            scanDevicesLocked();
            mNeedToSendFinishedDeviceScan = true;
        }
        // 进行设备的添加
        while (!mOpeningDevices.empty()) {
            /// 从mPendingEventItems读取事件项
            std::unique_ptr<Device> device = std::move(*mOpeningDevices.rbegin());
            mOpeningDevices.pop_back();
            ALOGV("Reporting device opened: id=%d, name=%s\n", device->id, device->path.c_str());
            event->when = now;
            event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
            event->type = DEVICE_ADDED;
            event += 1;

            // Try to find a matching video device by comparing device names
            for (auto it = mUnattachedVideoDevices.begin(); it != mUnattachedVideoDevices.end();
                 it++) {
                std::unique_ptr<TouchVideoDevice>& videoDevice = *it;
                if (tryAddVideoDeviceLocked(*device, videoDevice)) {
                    // videoDevice was transferred to 'device'
                    it = mUnattachedVideoDevices.erase(it);
                    break;
                }
            }

            auto [dev_it, inserted] = mDevices.insert_or_assign(device->id, std::move(device));
            if (!inserted) {
                ALOGW("Device id %d exists, replaced.", device->id);
            }
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }

        if (mNeedToSendFinishedDeviceScan) {
            mNeedToSendFinishedDeviceScan = false;
            event->when = now;
            event->type = FINISHED_DEVICE_SCAN;
            event += 1;
            if (--capacity == 0) {
                break;
            }
        }

        // Grab the next input event.
        bool deviceChanged = false;
        while (mPendingEventIndex < mPendingEventCount) {
            const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];
            if (eventItem.data.fd == mINotifyFd) {
                if (eventItem.events & EPOLLIN) {
                    mPendingINotify = true;
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for INotify.", eventItem.events);
                }
                continue;
            }

            if (eventItem.data.fd == mWakeReadPipeFd) {
                if (eventItem.events & EPOLLIN) {
                    ALOGV("awoken after wake()");
                    awoken = true;
                    char wakeReadBuffer[16];
                    ssize_t nRead;
                    do {
                        nRead = read(mWakeReadPipeFd, wakeReadBuffer, sizeof(wakeReadBuffer));
                    } while ((nRead == -1 && errno == EINTR) || nRead == sizeof(wakeReadBuffer));
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for wake read pipe.",
                          eventItem.events);
                }
                continue;
            }
            /// 根据eventItem.data.fd。获取设备ID所对应的devices
            Device* device = getDeviceByFdLocked(eventItem.data.fd);
            if (device == nullptr) {
                ALOGE("Received unexpected epoll event 0x%08x for unknown fd %d.", eventItem.events,
                      eventItem.data.fd);
                ALOG_ASSERT(!DEBUG);
                continue;
            }
            if (device->videoDevice && eventItem.data.fd == device->videoDevice->getFd()) {
                if (eventItem.events & EPOLLIN) {
                    size_t numFrames = device->videoDevice->readAndQueueFrames();
                    if (numFrames == 0) {
                        ALOGE("Received epoll event for video device %s, but could not read frame",
                              device->videoDevice->getName().c_str());
                    }
                } else if (eventItem.events & EPOLLHUP) {
                    // TODO(b/121395353) - consider adding EPOLLRDHUP
                    ALOGI("Removing video device %s due to epoll hang-up event.",
                          device->videoDevice->getName().c_str());
                    unregisterVideoDeviceFromEpollLocked(*device->videoDevice);
                    device->videoDevice = nullptr;
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for device %s.", eventItem.events,
                          device->videoDevice->getName().c_str());
                    ALOG_ASSERT(!DEBUG);
                }
                continue;
            }
            // This must be an input event
            if (eventItem.events & EPOLLIN) {
                /// 开始从设备中不断的读取事件，放到readerBuffer中。
                int32_t readSize =
                        read(device->fd, readBuffer, sizeof(struct input_event) * capacity);
                if (readSize == 0 || (readSize < 0 && errno == ENODEV)) {
                    // Device was removed before INotify noticed.
                    ALOGW("could not get event, removed? (fd: %d size: %" PRId32
                          " bufferSize: %zu capacity: %zu errno: %d)\n",
                          device->fd, readSize, bufferSize, capacity, errno);
                    deviceChanged = true;
                    //设备已被移除则执行关闭操作
                    closeDeviceLocked(*device);
                } else if (readSize < 0) {
                    if (errno != EAGAIN && errno != EINTR) {
                        ALOGW("could not get event (errno=%d)", errno);
                    }
                } else if ((readSize % sizeof(struct input_event)) != 0) {
                    ALOGE("could not get event (wrong size: %d)", readSize);
                } else {
                    int32_t deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;

                    size_t count = size_t(readSize) / sizeof(struct input_event);
                    for (size_t i = 0; i < count; i++) {
                        // 获取readBuffer的数据
                        struct input_event& iev = readBuffer[i];
                        // 将input_event信息, 封装成RawEvent
                        event->when = processEventTimestamp(iev);
                        event->readTime = systemTime(SYSTEM_TIME_MONOTONIC);
                        event->deviceId = deviceId;
                        event->type = iev.type;
                        event->code = iev.code;
                        event->value = iev.value;
                        event += 1;
                        capacity -= 1;
                    }
                    if (capacity == 0) {
                        // The result buffer is full.  Reset the pending event index
                        // so we will try to read the device again on the next iteration.
                        mPendingEventIndex -= 1;
                        break;
                    }
                }
            } else if (eventItem.events & EPOLLHUP) {
                ALOGI("Removing device %s due to epoll hang-up event.",
                      device->identifier.name.c_str());
                deviceChanged = true;
                closeDeviceLocked(*device);
            } else {
                ALOGW("Received unexpected epoll event 0x%08x for device %s.", eventItem.events,
                      device->identifier.name.c_str());
            }
        }

        // readNotify() will modify the list of devices so this must be done after
        // processing all other events to ensure that we read all remaining events
        // before closing the devices.
        if (mPendingINotify && mPendingEventIndex >= mPendingEventCount) {
            mPendingINotify = false;
            readNotifyLocked();
            deviceChanged = true;
        }

        // Report added or removed devices immediately.
        if (deviceChanged) {
            continue;
        }

        // Return now if we have collected any events or if we were explicitly awoken.
        if (event != buffer || awoken) {
            break;
        }

        // Poll for events.
        // When a device driver has pending (unread) events, it acquires
        // a kernel wake lock.  Once the last pending event has been read, the device
        // driver will release the kernel wake lock, but the epoll will hold the wakelock,
        // since we are using EPOLLWAKEUP. The wakelock is released by the epoll when epoll_wait
        // is called again for the same fd that produced the event.
        // Thus the system can only sleep if there are no events pending or
        // currently being processed.
        //
        // The timeout is advisory only.  If the device is asleep, it will not wake just to
        // service the timeout.
        mPendingEventIndex = 0;
        // poll之前先释放锁
        mLock.unlock(); // release lock before poll
        // 等待input事件的到来
        int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);
        // poll之后再次请求锁
        mLock.lock(); // reacquire lock after poll

        if (pollResult == 0) {
            // Timed out.
            mPendingEventCount = 0;
            break;
        }
        //出现错误
        if (pollResult < 0) {
            // An error occurred.
            // 系统发生错误则休眠1s
            mPendingEventCount = 0;

            // Sleep after errors to avoid locking up the system.
            // Hopefully the error is transient.
            if (errno != EINTR) {
                ALOGW("poll failed (errno=%d)\n", errno);
                usleep(100000);
            }
        } else {
            // Some events occurred.
            mPendingEventCount = size_t(pollResult);
        }
    }

    // All done, return the number of events we read.
    // 返回所读取的事件个数
    return event - buffer;
}

EventHub采用INotify + epoll机制实现监听目录/dev/input下的设备节点，经过EventHub将input_event结构体 + deviceId 转换成RawEvent结构体

所以这里我们可以看到EventHub进行消息的监听也是使用INotify + epoll机制。有点类似于Handler机制。

RawEvent

/*
 * A raw event as retrieved from the EventHub.
 * 
 */
struct RawEvent {
    nsecs_t when;           //时间发生的时间点
    int32_t deviceId;       // 产生事件的设备ID
    int32_t type;           // 事件的类型：DEVICE_ADDED(添加)、DEVICE_REMOVED(删除)、
                            // FINISHED_DEVICE_SCAN(扫描完成)、type<FIRST_SYNTHETIC_EVENT(其他事件)
    int32_t code;
    int32_t value;
};

此处事件类型:

• DEVICE_ADDED(添加)

• DEVICE_REMOVED(删除)

• FINISHED_DEVICE_SCAN(扫描完成)

• type<FIRST_SYNTHETIC_EVENT(其他事件)

getEvents()已完成转换事件转换工作, 接下来,顺便看看设备扫描过程.

EventHub::scanDevicesLocked

/**
 * frameworks/native/services/inputflinger/reader/EventHub.cpp
 **/
void EventHub::scanDevicesLocked() {
    // 此处DEVICE_PATH="/dev/input"
    status_t result = scanDirLocked(DEVICE_PATH);
    if (result < 0) {
        ALOGE("scan dir failed for %s", DEVICE_PATH);
    }
    if (isV4lScanningEnabled()) {
        result = scanVideoDirLocked(VIDEO_DEVICE_PATH);
        if (result != OK) {
            ALOGE("scan video dir failed for %s", VIDEO_DEVICE_PATH);
        }
    }
    if (mDevices.indexOfKey(ReservedInputDeviceId::VIRTUAL_KEYBOARD_ID) < 0) {
        createVirtualKeyboardLocked();
    }
}

EventHub::scanDirLocked

status_t EventHub::scanDirLocked(const std::string& dirname) {
    for (const auto& entry : std::filesystem::directory_iterator(dirname)) {
        openDeviceLocked(entry.path());
    }
    return 0;
}

status_t EventHub::scanDirLocked(const char* dirname) {
    char devname[PATH_MAX];
    char* filename;
    DIR* dir;
    struct dirent* de;
    dir = opendir(dirname);
    if (dir == nullptr) return -1;
    strcpy(devname, dirname);
    filename = devname + strlen(devname);
    *filename++ = '/';
    // 读取/dev/input/目录下所有的设备节点
    while ((de = readdir(dir))) {
        if (de->d_name[0] == '.' &&
            (de->d_name[1] == '\0' || (de->d_name[1] == '.' && de->d_name[2] == '\0')))
            continue;
        strcpy(filename, de->d_name);
        //打开相应的设备节点
        openDeviceLocked(devname);
    }
    closedir(dir);
    return 0;
}

EventHub::openDirLocked

status_t EventHub::openDeviceLocked(const char *devicePath) {
    char buffer[80];
    //打开设备文件
    int fd = open(devicePath, O_RDWR | O_CLOEXEC);
    InputDeviceIdentifier identifier;
    //获取设备名
    if(ioctl(fd, EVIOCGNAME(sizeof(buffer) - 1), &buffer) < 1){
    } else {
        buffer[sizeof(buffer) - 1] = '\0';
        identifier.name.setTo(buffer);
    }

    identifier.bus = inputId.bustype;
    identifier.product = inputId.product;
    identifier.vendor = inputId.vendor;
    identifier.version = inputId.version;

    //获取设备物理地址
    if(ioctl(fd, EVIOCGPHYS(sizeof(buffer) - 1), &buffer) < 1) {
    } else {
        buffer[sizeof(buffer) - 1] = '\0';
        identifier.location.setTo(buffer);
    }

    //获取设备唯一ID
    if(ioctl(fd, EVIOCGUNIQ(sizeof(buffer) - 1), &buffer) < 1) {
    } else {
        buffer[sizeof(buffer) - 1] = '\0';
        identifier.uniqueId.setTo(buffer);
    }
    //将identifier信息填充到fd
    assignDescriptorLocked(identifier);
    //设置fd为非阻塞方式
    fcntl(fd, F_SETFL, O_NONBLOCK);

    //获取设备ID，分配设备对象内存
    int32_t deviceId = mNextDeviceId++;
    Device* device = new Device(fd, deviceId, String8(devicePath), identifier);
    ...

    //注册epoll
    struct epoll_event eventItem;
    memset(&eventItem, 0, sizeof(eventItem));
    eventItem.events = EPOLLIN;
    if (mUsingEpollWakeup) {
        eventItem.events |= EPOLLWAKEUP;
    }
    eventItem.data.u32 = deviceId;
    if (epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, &eventItem)) {
        delete device; //添加失败则删除该设备
        return -1;
    }
    ...
    //【见小节2.2.4】
    addDeviceLocked(device);
}

EventHub::addDeviceLocked

/**
 *  代码位于：frameworks/native/services/inputflinger/reader/EventHub.cpp
 **/
void EventHub::addDeviceLocked(std::unique_ptr<Device> device) {
    // 添加到mDevices队列
    reportDeviceAddedForStatisticsLocked(device->identifier, device->classes);
    mOpeningDevices.push_back(std::move(device));
}

介绍了EventHub从设备节点获取事件的流程，当收到事件后接下里便开始处理事件。

InputReader::processEventsLocked

/**
 * 代码位于：frameworks/native/services/inputflinger/reader/InputReader.cpp
 **/
void InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
    for (const RawEvent* rawEvent = rawEvents; count;) {
        int32_t type = rawEvent->type;
        size_t batchSize = 1;
        if (type < EventHubInterface::FIRST_SYNTHETIC_EVENT) {
            int32_t deviceId = rawEvent->deviceId;
            while (batchSize < count) {
                if (rawEvent[batchSize].type >= EventHubInterface::FIRST_SYNTHETIC_EVENT ||
                    rawEvent[batchSize].deviceId != deviceId) {
                    break;
                }
                // 同一设备的事件打包处理
                batchSize += 1;
            }
            if (DEBUG_RAW_EVENTS) {
                ALOGD("BatchSize: %zu Count: %zu", batchSize, count);
            }
            // 数据事件的处理
            processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
        } else {
            switch (rawEvent->type) {
                case EventHubInterface::DEVICE_ADDED:
                    // 设备添加
                    addDeviceLocked(rawEvent->when, rawEvent->deviceId);
                    break;
                case EventHubInterface::DEVICE_REMOVED:
                    // 设备移除
                    removeDeviceLocked(rawEvent->when, rawEvent->deviceId);
                    break;
                case EventHubInterface::FINISHED_DEVICE_SCAN:
                    // 设备扫描完成
                    handleConfigurationChangedLocked(rawEvent->when);
                    break;
                default:
                    //  不会发生
                    ALOG_ASSERT(false); // can't happen
                    break;
            }
        }
        count -= batchSize;
        rawEvent += batchSize;
    }
}

事件处理总共有下几类类型：

• DEVICE_ADDED(设备增加), [见小节3.2]
• DEVICE_REMOVED(设备移除)
• FINISHED_DEVICE_SCAN(设备扫描完成)
• 数据事件[见小节3.4]

先来说说DEVICE_ADDED设备增加的过程。

InputReader::addDeviceLocked

/**
 * 代码位于：frameworks/native/services/inputflinger/reader/InputReader.cpp
 */
void InputReader::addDeviceLocked(nsecs_t when, int32_t eventHubId) {
    // 已添加的相同设备则不再添加
    if (mDevices.find(eventHubId) != mDevices.end()) {
        ALOGW("Ignoring spurious device added event for eventHubId %d.", eventHubId);
        return;
    }

    InputDeviceIdentifier identifier = mEventHub->getDeviceIdentifier(eventHubId);
    // 进行设备的创建
    std::shared_ptr<InputDevice> device = createDeviceLocked(eventHubId, identifier);
    device->configure(when, &mConfig, 0);
    device->reset(when);
    // 
    if (device->isIgnored()) {
        ALOGI("Device added: id=%d, eventHubId=%d, name='%s', descriptor='%s' "
              "(ignored non-input device)",
              device->getId(), eventHubId, identifier.name.c_str(), identifier.descriptor.c_str());
    } else {
        ALOGI("Device added: id=%d, eventHubId=%d, name='%s', descriptor='%s',sources=%s",
              device->getId(), eventHubId, identifier.name.c_str(), identifier.descriptor.c_str(),
              inputEventSourceToString(device->getSources()).c_str());
    }
    // 添加设备到mDevices
    mDevices.emplace(eventHubId, device);
    // Add device to device to EventHub ids map.
    const auto mapIt = mDeviceToEventHubIdsMap.find(device);
    if (mapIt == mDeviceToEventHubIdsMap.end()) {
        std::vector<int32_t> ids = {eventHubId};
        mDeviceToEventHubIdsMap.emplace(device, ids);
    } else {
        mapIt->second.push_back(eventHubId);
    }
    bumpGenerationLocked();

    if (device->getClasses().test(InputDeviceClass::EXTERNAL_STYLUS)) {
        notifyExternalStylusPresenceChangedLocked();
    }

    // Sensor input device is noisy, to save power disable it by default.
    // Input device is classified as SENSOR when any sub device is a SENSOR device, check Eventhub
    // device class to disable SENSOR sub device only.
    if (mEventHub->getDeviceClasses(eventHubId).test(InputDeviceClass::SENSOR)) {
        mEventHub->disableDevice(eventHubId);
    }
}

InputReader::addDeviceLocked

归纳总结

Android 系统是由事件驱动的，而 input 是最常见的事件之一，用户的点击、滑动、长按等操作，都属于 input 事件驱动，其中的核心就是 InputReader 和 InputDispatcher。InputReader 和 InputDispatcher 是跑在 SystemServer进程中的两个 native 循环线程，负责读取和分发 Input 事件。整个处理过程大致流程如下：

InputReader整个过程涉及多次事件封装转换，其主要工作核心是以下三大步骤:

• 首先，system_server进程中的native线程的InputReader利用linux的epolle机制监听并且从屏幕驱动读取上报的事件。通过EventHub(监听目录/dev/input)读取事件放入mEventBuffer,而mEventBuffer是一个大小为256的数组, 再将事件input_event转换为RawEvent;
• processEventsLocked: 对事件进行加工, 转换RawEvent -> NotifyKeyArgs(NotifyArgs)
• QueuedListener->flush：将事件发送到InputDispatcher线程, 转换NotifyKeyArgs -> KeyEntry(EventEntry)

InputReader线程不断循环地执行InputReader.loopOnce(), 每次处理完生成的是EventEntry(比如KeyEntry, MotionEntry), 接下来的工作就交给InputDispatcher线程。

InputReader线程不断循环地执行InputReader.loopOnce(), 每次处理完生成的是EventEntry(比如KeyEntry, MotionEntry), 接下来的工作就交给InputDispatcher线程。