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;
}a
ddDeviceLocked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。
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。。。。
。。。。。。