android 管道模式,Android 输入系统（二）EventHub

接着上一篇的InputManagerService，这里主要介绍一下EventHub。EventHub主要是访问/dev/input下的所有设备节点，并将输入事件、设备节点的增删返给InputReader。

1 EventHub初始化

由上一篇可知，EventHub对象是在NativeInputManager构造函数中创建的。先看一下EventHub构造函数中都做了些什么

EventHub::EventHub(void) :

mBuiltInKeyboardId(NO_BUILT_IN_KEYBOARD), mNextDeviceId(1),

mOpeningDevices(0), mClosingDevices(0),

mNeedToSendFinishedDeviceScan(false),

mNeedToReopenDevices(false), mNeedToScanDevices(true),

mPendingEventCount(0), mPendingEventIndex(0), mPendingINotify(false) {

acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);

//创建epoll对象，mEpollFd为epoll对象的描述符

mEpollFd = epoll_create(EPOLL_SIZE_HINT);

LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance.  errno=%d", errno);

//创建inotify对象，mINotifyFd为inotify对象的描述符

mINotifyFd = inotify_init();

//DEVICE_PATH值为"/dev/input"，监听该目录下的设备节点创建与删除操作。通过read函数读取事件。

int result = inotify_add_watch(mINotifyFd, DEVICE_PATH, IN_DELETE | IN_CREATE);

LOG_ALWAYS_FATAL_IF(result < 0, "Could not register INotify for %s.  errno=%d",

DEVICE_PATH, errno);

struct epoll_event eventItem;

memset(&eventItem, 0, sizeof(eventItem));

eventItem.events = EPOLLIN;    //监听可读事件

eventItem.data.u32 = EPOLL_ID_INOTIFY;

//EPOLL_CTL_ADD表示增加事件

//epoll_ctl将事件监听添加到epoll对象中去。

result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mINotifyFd, &eventItem);

LOG_ALWAYS_FATAL_IF(result != 0, "Could not add INotify to epoll instance.  errno=%d", errno);

int wakeFds[2];

result = pipe(wakeFds);

LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe.  errno=%d", errno);

mWakeReadPipeFd = wakeFds[0];

mWakeWritePipeFd = wakeFds[1];

result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);

LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake read pipe non-blocking.  errno=%d",

errno);

result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);

LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake write pipe non-blocking.  errno=%d",

errno);

eventItem.data.u32 = EPOLL_ID_WAKE;

result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, &eventItem);

LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake read pipe to epoll instance.  errno=%d",

errno);

}

这段代码主要工作：

1.初始化一些成员变量

2.创建epoll对象，EPOLL_SIZE_HINT = 8代表最大监听数为8.

3.创建inotify对象，监听/dev/input下设备节点的增删。

4.将mINotifyFd添加到epoll中，作为一个监控对象。

5.创建管道，将管道读取端的可读事件添加到epoll中。使epoll_wait()返回，唤醒InputReader线程。

2 EventHub::getEvents()

EventHub的主要工作都是在getEvents函数中，InputReaderThread通过循环调用EventHub的getEvents()函数获取输入事件。getEvents中做了些什么，现在看一看。

size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {

ALOG_ASSERT(bufferSize >= 1);

AutoMutex _l(mLock);

struct input_event readBuffer[bufferSize];

//每存一个事件，event指针向后移动一个元素。

RawEvent* event = buffer;

//capacity存buffer中剩余端元素数量，capacity为0，表示buffer已满。

size_t capacity = bufferSize;

bool awoken = false;

for (;;) {

...............

//循环体。

}

// All done, return the number of events we read.

return event - buffer;

}

以上是getEvents()的整体模型，接着看循环体中的方法。

2.1 重新打开设备(mNeedToReopenDevices)

//获取系统当前时间(native层的方法)。

nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);

// Reopen input devices if needed.

if (mNeedToReopenDevices) {//判断是否需要重新打开设备

mNeedToReopenDevices = false;

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

closeAllDevicesLocked();//关闭、卸载所有设备

mNeedToScanDevices = true; //下次扫描设备

break; // return to the caller before we actually rescan

}

由EventHub构造函数可知mNeedToReopenDevices为初始值false，第一次调用getEvents()时不会运行上面的代码块。其中调用了closeAllDevicesLocked()函数

void EventHub::closeAllDevicesLocked() {

while (mDevices.size() > 0) {

closeDeviceLocked(mDevices.valueAt(mDevices.size() - 1));

}

}

closeAllDevicesLocked()函数中遍历mDevices,通过closeDeviceLocked()函数卸载所有这些设备。closeDeviceLocked()函数如下

void EventHub::closeDeviceLocked(Device* device) {

ALOGI("Removed device: path=%s name=%s id=%d fd=%d classes=0x%x\n",

device->path.string(), device->identifier.name.string(), device->id,

device->fd, device->classes);

if (device->id == mBuiltInKeyboardId) {

ALOGW("built-in keyboard device %s (id=%d) is closing! the apps will not like this",

device->path.string(), mBuiltInKeyboardId);

mBuiltInKeyboardId = NO_BUILT_IN_KEYBOARD;

}

//判断是否是虚拟设备

if (!device->isVirtual()) {

//从epoll中删除对这些设备的监听

if (epoll_ctl(mEpollFd, EPOLL_CTL_DEL, device->fd, NULL)) {

ALOGW("Could not remove device fd from epoll instance.  errno=%d", errno);

}

}

//移除设备

mDevices.removeItem(device->id);

device->close();

// Unlink for opening devices list if it is present.

Device* pred = NULL;

bool found = false;

for (Device* entry = mOpeningDevices; entry != NULL; ) {

if (entry == device) {

found = true;

break;

}

pred = entry;

entry = entry->next;

}

if (found) {

// Unlink the device from the opening devices list then delete it.

// We don't need to tell the client that the device was closed because

// it does not even know it was opened in the first place.

ALOGI("Device %s was immediately closed after opening.", device->path.string());

if (pred) {

pred->next = device->next;

} else {

mOpeningDevices = device->next;

}

delete device;

} else {

// Link into closing devices list.

// The device will be deleted later after we have informed the client.

//把这些设备添加到mClosingDevices，用来生成DEVICE_REMOVED事件

device->next = mClosingDevices;

mClosingDevices = device;

}

}

closeDeviceLocked()函数主要工作：

1.从Epoll中删除监听(EPOLL_CTL_DEL)。

2.mDevices中删除Device对象

3.将删除端Device对象添加到mClosingDevices中。用于之后向InputReader发送DEVICE_REMOVED事件

2.2 DEVICE_REMOVED事件(mClosingDevices)

// Report any devices that had last been added/removed.

//遍历mClosingDevices，生成DEVICE_REMOVED事件

while (mClosingDevices) {

Device* device = mClosingDevices;

ALOGV("Reporting device closed: id=%d, name=%s\n",

device->id, device->path.string());

mClosingDevices = device->next;

event->when = now;//设置事件的时间戳

event->deviceId = device->id == mBuiltInKeyboardId ? BUILT_IN_KEYBOARD_ID : device->id;    //设置事件对应的设备id

event->type = DEVICE_REMOVED;   //设在事件类型DEVICE_REMOVED

event += 1;                  //event指向下一个RawEvent对象

delete device;            //释放不需要的device

mNeedToSendFinishedDeviceScan = true;

//capacity为0时，表示buffer已满，则停止循环将事件返回给调用者(也就是InputReader)，剩余的事件等下次getEvents调用

if (--capacity == 0) {

break;

}

}

mClosingDevices初始值为0，所以刚开始调用getEvents()函数不会运行上述代码块。该块中主要是遍历mClosingDevices，生成DEVICE_REMOVED事件。

2.3 扫描加载设备(mNeedToScanDevices)

if (mNeedToScanDevices) {

mNeedToScanDevices = false;

scanDevicesLocked();    //打开/dev/input下所有输入设备

mNeedToSendFinishedDeviceScan = true;

}

mNeedToScanDevices初始值为true，所以第一次getEvents会运行该代码块。该代码块主要工作：

1 mNeedToScanDevices赋值为false，避免重复扫描打开设备。

2 调用scanDevicesLocked()，//打开/dev/input下所有输入设备。

3 mNeedToSendFinishedDeviceScan赋值为true，用于生成FINISHED_DEVICE_SCAN事件。

接着看一下scanDevicesLocked()函数

void EventHub::scanDevicesLocked() {

status_t res = scanDirLocked(DEVICE_PATH);

if(res < 0) {

ALOGE("scan dir failed for %s\n", DEVICE_PATH);

}

//创建一个虚拟的输入设备(这个不太清楚)。

if (mDevices.indexOfKey(VIRTUAL_KEYBOARD_ID) < 0) {

createVirtualKeyboardLocked();

}

}

scanDevicesLocked()函数中调用了scanDirLocked()函数，接着看scanDirLocked()函数：

status_t EventHub::scanDirLocked(const char *dirname)

{

char devname[PATH_MAX];

char *filename;

DIR *dir;

struct dirent *de;

dir = opendir(dirname);

if(dir == NULL)

return -1;

strcpy(devname, dirname);

filename = devname + strlen(devname);

*filename++ = '/';

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);

openDeviceLocked(devname); //

}

closedir(dir);

return 0;

}

scanDirLocked()函数遍历/dev/input文件夹下的所有设备节点，并分别执行openDeviceLocked(devname)，加载设备。openDeviceLocked()函数比较长，就不全部贴出来了，只将一些重要的部分弄出来。

status_t EventHub::openDeviceLocked(const char *devicePath) {

//打开设备节点

int fd = open(devicePath, O_RDWR | O_CLOEXEC);

if(fd < 0) {

ALOGE("could not open %s, %s\n", devicePath, strerror(errno));

return -1;

}

//获取device的name、driver version、id等。

。。。。。。

//创建Device

int32_t deviceId = mNextDeviceId++;

Device* device = new Device(fd, deviceId, String8(devicePath), identifier);

。。。。。。

// Load the configuration file for the device. 加载配置信息

loadConfigurationLocked(device);

// Figure out the kinds of events the device reports.

//设置device->classes，为设备分配类别(鼠标、键盘、触摸板等)

// Register with epoll.将设备节点描述符的可读事件添加到Epoll中。

struct epoll_event eventItem;

memset(&eventItem, 0, sizeof(eventItem));

eventItem.events = EPOLLIN;

eventItem.data.u32 = deviceId;   //设备id

if (epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, &eventItem)) {

ALOGE("Could not add device fd to epoll instance.  errno=%d", errno);

delete device;

return -1;

}

。。。。。

//将device添加到mDevice中。

addDeviceLocked(device);

return 0;

}

addDeviceLocked将Device添加到mDevice中，同时也会添加到mOpeningDevices中，用来生成DEVICE_ADDED事件，发送给InputReader。这之后就可以通过getEvents读取到设备产生的输入事件了。

2.4 DEVICE_ADDED事件(mOpeningDevices)

while (mOpeningDevices != NULL) {

Device* device = mOpeningDevices;

ALOGD("Reporting device opened: id=%d, name=%s\n",

device->id, device->path.string());

mOpeningDevices = device->next;

event->when = now;        //设置事件端时间戳

event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;

event->type = DEVICE_ADDED;        //设置事件类型DEVICE_ADDED

event += 1;                //event指向下一个RawEvent对象,用于填写下一次事件

mNeedToSendFinishedDeviceScan = true;

if (--capacity == 0) {      //查看buffer是否已满

break;

}

}

由于上面scanDevicesLocked时将/dev/input下的设备节点打开，并添加到mOpeningDevices中，所以会运行此代码块。这里主要是遍历mOpeningDevices，设置DEVICE_ADDED事件。

2.5 FINISHED_DEVICE_SCAN事件(mNeedToSendFinishedDeviceScan)

if (mNeedToSendFinishedDeviceScan) {

mNeedToSendFinishedDeviceScan = false;

event->when = now;          //设置事件端时间戳

event->type = FINISHED_DEVICE_SCAN;    //设置事件类型FINISHED_DEVICE_SCAN

event += 1;

if (--capacity == 0) {

break;

}

}

上述三个代码块都会将mNeedToSendFinishedDeviceScan设为true，所以接着生成FINISHED_DEVICE_SCAN类型的事件。也就是当设备增删事件后，需要向getEvents()函数调用者发送FINISHED_DEVICE_SCAN事件。

由代码顺序可以知道DEVICE_REMOVED事件优先级最高、然后DEVICE_ADDED事件、FINISHED_DEVICE_SCAN事件最低。只有高优先级的事件处理完之后才会处理低优先级的事件。

2.6 iNotify事件、管道事件

接着是while循环，检查是否有未处理的设备事件。

while (mPendingEventIndex < mPendingEventCount) {

const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];

//EPOLL_ID_INOTIFY是EventHub初始化时，用来检测/dev/input下添加、删除设备事件。

if (eventItem.data.u32 == EPOLL_ID_INOTIFY) {

if (eventItem.events & EPOLLIN) {

mPendingINotify = true;    //符合条件标记inotify事件待处理。

} else {

ALOGW("Received unexpected epoll event 0x%08x for INotify.", eventItem.events);

}

continue;//继续处理mPendingEventItems中的事件

}

。。。。。。

}

// 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.

//判断是否有待处理的inotify事件。

if (mPendingINotify && mPendingEventIndex >= mPendingEventCount) {

mPendingINotify = false;

readNotifyLocked();

deviceChanged = true;

}

ALOGD("getEvents -----9 deviceChanged:%d",deviceChanged);

// Report added or removed devices immediately.

if (deviceChanged) {

continue;//如果处理有inotify事件，处理后，进行下一次循环，生成设备增删事件。

}

。。。。。。

mPendingINotify赋值为false，表示之后没有待处理的inotify事件。

readNotifyLocked() 处理inotify事件。

deviceChanged设置为true，进行下一次循环，生成设备增删事件。

接着看一下readNotifyLocked()函数中做了些什么。

status_t EventHub::readNotifyLocked() {

int res;

char devname[PATH_MAX];

char *filename;

char event_buf[512];

int event_size;

int event_pos = 0;

struct inotify_event *event;

ALOGD("EventHub::readNotify nfd: %d\n", mINotifyFd);

//从mINotifyFd读取inotify事件，存到event_buf中，

res = read(mINotifyFd, event_buf, sizeof(event_buf));

if(res < (int)sizeof(*event)) {

if(errno == EINTR)

return 0;

ALOGW("could not get event, %s\n", strerror(errno));

return -1;

}

//printf("got %d bytes of event information\n", res);

strcpy(devname, DEVICE_PATH);

filename = devname + strlen(devname);

*filename++ = '/';

while(res >= (int)sizeof(*event)) {

event = (struct inotify_event *)(event_buf + event_pos);

//printf("%d: %08x \"%s\"\n", event->wd, event->mask, event->len ? event->name : "");

if(event->len) {

strcpy(filename, event->name);

if(event->mask & IN_CREATE) {//判断事件类型是否是IN_CREATE

openDeviceLocked(devname);    //加载对应设备

} else {                //事件类型不是IN_CREATE，则是IN_DELETE

ALOGI("Removing device '%s' due to inotify event\n", devname);

closeDeviceByPathLocked(devname);  //卸载对应设备

}

}

//移动到下一个事件。

event_size = sizeof(*event) + event->len;

res -= event_size;

event_pos += event_size;

}

return 0;

}

主要工作

1 通过read()函数读取iNotify事件

2 遍历所有的iNotify事件

3 判断iNotify事件类型，IN_CREATE类型则加载设备，IN_DELETE类型则卸载设备。

接着是判断是否是管道事件

while (mPendingEventIndex < mPendingEventCount) {

。。。。。

if (eventItem.data.u32 == EPOLL_ID_WAKE) {

if (eventItem.events & EPOLLIN) {

ALOGD("awoken after wake()");

awoken = true; //用来唤醒InputRead线程

char buffer[16];

ssize_t nRead;

do {//从mWakeReadPipeFd读取管道事件

nRead = read(mWakeReadPipeFd, buffer, sizeof(buffer));

} while ((nRead == -1 && errno == EINTR) || nRead == sizeof(buffer));

} else {

ALOGW("Received unexpected epoll event 0x%08x for wake read pipe.",

eventItem.events);

}

continue;

}

。。。。

}

。。。。

// Return now if we have collected any events or if we were explicitly awoken.

if (event != buffer || awoken) {

break; //退出循环返回到InputReader。

}

2.7 输入事件

接着到输入事件了。根据输入事件，进行设置时间戳、id、类型、值等。拥有返回给调用者InputReader。

while (mPendingEventIndex < mPendingEventCount) {

。。。。。

//通过eventItem.data.u32 获取设备id

ssize_t deviceIndex = mDevices.indexOfKey(eventItem.data.u32);

if (deviceIndex < 0) {

ALOGW("Received unexpected epoll event 0x%08x for unknown device id %d.",

eventItem.events, eventItem.data.u32);

continue;

}

//从mDevices获取设备

Device* device = mDevices.valueAt(deviceIndex);

if (eventItem.events & EPOLLIN) {//epoll事件是EPOLLIN，可读，读取结果保存在readBuffer中，capacity是限制一次读取事件的个数

int32_t readSize = read(device->fd, readBuffer,

sizeof(struct input_event) * capacity);

if (readSize == 0 || (readSize < 0 && errno == ENODEV)) {

//读取有问题

// Device was removed before INotify noticed.

ALOGW("could not get event, removed? (fd: %d size: %d bufferSize: %d "

"capacity: %d errno: %d)\n",

device->fd, readSize, bufferSize, capacity, errno);

deviceChanged = true;

closeDeviceLocked(device);//关闭该设备

} 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);

//遍历所有读取的输入事件

for (size_t i = 0; i < count; i++) {

struct input_event& iev = readBuffer[i];

if (iev.type == EV_MSC) {

if (iev.code == MSC_ANDROID_TIME_SEC) {

device->timestampOverrideSec = iev.value;

continue;

} else if (iev.code == MSC_ANDROID_TIME_USEC) {

device->timestampOverrideUsec = iev.value;

continue;

}

}

if (device->timestampOverrideSec || device->timestampOverrideUsec) {

iev.time.tv_sec = device->timestampOverrideSec;

iev.time.tv_usec = device->timestampOverrideUsec;

if (iev.type == EV_SYN && iev.code == SYN_REPORT) {

device->timestampOverrideSec = 0;

device->timestampOverrideUsec = 0;

}

ALOGV("applied override time %d.%06d",

int(iev.time.tv_sec), int(iev.time.tv_usec));

}

#ifdef HAVE_POSIX_CLOCKS

//设置更准确的时间

event->when = nsecs_t(iev.time.tv_sec) * 1000000000LL

+ nsecs_t(iev.time.tv_usec) * 1000LL;

ALOGV("event time %lld, now %lld", event->when, now);

if (event->when >= now + 10 * 1000000000LL) {

// Double-check.  Time may have moved on.

nsecs_t time = systemTime(SYSTEM_TIME_MONOTONIC);

if (event->when > time) {

ALOGW("An input event from %s has a timestamp that appears to "

"have been generated using the wrong clock source "

"(expected CLOCK_MONOTONIC): "

"event time %lld, current time %lld, call time %lld.  "

"Using current time instead.",

device->path.string(), event->when, time, now);

event->when = time;

} else {

ALOGV("Event time is ok but failed the fast path and required "

"an extra call to systemTime: "

"event time %lld, current time %lld, call time %lld.",

event->when, time, now);

}

}

#else

event->when = now;

#endif

//设置一些信息

event->deviceId = deviceId;

event->type = iev.type;

event->code = iev.code;

event->value = iev.value;

event += 1;  //移动到下一该可用元素

capacity -= 1;    //可用数量减少1

}

if (capacity == 0) {//buffer存满了，mPendingEventIndex至为-1，下一次循环处理未完的事件。

// 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) {//事件类型为挂起

ALOGI("Removing device %s due to epoll hang-up event.",

device->identifier.name.string());

deviceChanged = true;

closeDeviceLocked(device);    //卸载设备

} else {

ALOGW("Received unexpected epoll event 0x%08x for device %s.",

eventItem.events, device->identifier.name.string());

}

}

。。。。。。

rerutn event-buffer;//返回事件数量

}

while循环后面是判断是否有inotify事件，wake事件。接着是获取epoll事件 。先获取到epoll事件，下次循环才会处理while循环。

通过mEpollFd描述符，获取epoll事件。保存在mPendingEventItems中，EPOLL_MAX_EVENTS(16)为限制一次最大读取事件次数，timeoutMillis为超时时间。

mPendingEventIndex = 0;

mLock.unlock(); // release lock before poll, must be before release_wake_lock

release_wake_lock(WAKE_LOCK_ID);

//等待事件

int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);

acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);

mLock.lock(); // reacquire lock after poll, must be after acquire_wake_lock

if (pollResult == 0) {

// Timed out.

mPendingEventCount = 0;

break;

}

if (pollResult < 0) {

// An error occurred.

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.

//保存epoll事件数量，用于下次for循环处理

mPendingEventCount = size_t(pollResult);

}

}

到现在getEvents函数基本上就完了。还有许多内容待揣摩。

3 总结

EventHub主要工作：设备管理(加载、卸载)、输入事件读取。核心代码就是getEvent()，该代码中完成了这些事情。

其中使用到的epoll、inotify、管道这些技术可以好好研究下。。。。

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