Android 中input event的分析
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文章將分析Android 的Input Event 子系統的來龍去脈。
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Android 系統里面有很多小工具，運行這些工具，我們對它們有一個感性的認識，進而閱讀和分析這些小工具源代碼，再順藤摸瓜，就可以把整個子系統的來龍去脈弄清楚。
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1.運行toolbox的getevent 工具。
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# getevent -help
getevent -help
Usage: getevent [-t] [-n] [-s switchmask] [-S] [-v [mask]] [-p] [-q] [-c count] [-r] [device]
??? -t: show time stamps
??? -n: don't print newlines
??? -s: print switch states for given bits
??? -S: print all switch states
??? -v: verbosity mask (errs=1, dev=2, name=4, info=8, vers=16, pos. events=32)
??? -p: show possible events (errs, dev, name, pos. events)
??? -q: quiet (clear verbosity mask)
??? -c: print given number of events then exit
??? -r: print rate events are received
# getevent -c 20
getevent -c 20
add device 1: /dev/input/event4
? name:???? "sensor-input"
add device 2: /dev/input/event3
? name:???? "88pm860x_hook"
add device 3: /dev/input/event2
? name:???? "88pm860x_on"
add device 4: /dev/input/event1
? name:???? "88pm860x-touch"
add device 5: /dev/input/event0
? name:???? "pxa27x-keypad"
/dev/input/event0: 0001 0066 00000001
/dev/input/event0: 0000 0000 00000000
/dev/input/event0: 0001 0066 00000000
/dev/input/event0: 0000 0000 00000000
/dev/input/event1: 0003 0000 00000c48
/dev/input/event1: 0003 0001 00000751
/dev/input/event1: 0001 014a 00000001
/dev/input/event1: 0000 0000 00000000
/dev/input/event1: 0003 0000 00000c67
/dev/input/event1: 0003 0001 000006f9
/dev/input/event1: 0000 0000 00000000
/dev/input/event1: 0003 0000 00000c9e
/dev/input/event1: 0003 0001 0000069e
/dev/input/event1: 0000 0000 00000000
/dev/input/event1: 0003 0000 00000cc4
/dev/input/event1: 0003 0001 00000620
/dev/input/event1: 0000 0000 00000000
/dev/input/event1: 0003 0000 00000ce8
/dev/input/event1: 0003 0001 000005ba
/dev/input/event1: 0000 0000 00000000
運行這個工具，然后按鍵或者滑動觸摸屏，會看到程序會實時打印event。從上面的輸出來看，系統有5個input 子系統。它們分別是
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add device 1: /dev/input/event4
? name:???? "sensor-input"
#Sensor input 子系統
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add device 2: /dev/input/event3
? name:???? "88pm860x_hook"
#耳機Hook鍵子系統。可支持接電話掛電話的耳機上面有一個按鍵，對應的就是這個input 子系統。
add device 3: /dev/input/event2
? name:???? "88pm860x_on"
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#開機鍵 input 子系統
add device 4: /dev/input/event1
? name:???? "88pm860x-touch"
#Touch Screen input 子系統
add device 5: /dev/input/event0
? name:???? "pxa27x-keypad"
#按鍵子系統，包括Home/Menu/Back等按鍵。
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可以嘗試多種event，實際感覺一下出來的log。
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2.閱讀getevent的代碼。代碼為./core/toolbox/getevent.c
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從代碼中，我們知道，程序在while(1)的一個死循環里，不斷地在讀取 (select 操作)/dev/input?下面的文件，檢查是否Kernel往里面更新內容，如果有內容更新，就把它打印出來。并且從代碼中，我們還知道，任何一個event都有三種屬性，type,code,value.
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??? while(1) {
??????? pollres = poll(ufds, nfds, -1);?
??????? //printf("poll %d, returned %d/n", nfds, pollres);
??????? if(ufds[0].revents & POLLIN) {
??????????? read_notify(device_path, ufds[0].fd, print_flags);
??????? }
??????? for(i = 1; i < nfds; i++) {
??????????? if(ufds[i].revents) {
??????????????? if(ufds[i].revents & POLLIN) {
??????????????????? res = read(ufds[i].fd, &event, sizeof(event));?
??????????????????? if(res < (int)sizeof(event)) {
??????????????????????? fprintf(stderr, "could not get event/n");
??????????????????????? return 1;
??????????????????? }
??????????????????? if(get_time) {
??????????????????????? printf("%ld-%ld: ", event.time.tv_sec, event.time.tv_usec);
??????????????????? }
??????????????????? if(print_device)
??????????????????????? printf("%s: ", device_names[i]);
??????????????????? printf("%04x %04x %08x", event.type, event.code, event.value);
??????????????????? if(sync_rate && event.type == 0 && event.code == 0) {
??????????????????????? int64_t now = event.time.tv_sec * 1000000LL + event.time.tv_usec;
??????????????????????? if(last_sync_time)
??????????????????????????? printf(" rate %lld", 1000000LL / (now - last_sync_time));
??????????????????????? last_sync_time = now;
??????????????????? }
??????????????????? printf("%s", newline);
??????????????????? if(event_count && --event_count == 0)
??????????????????????? return 0;
??????????????? }
??????????? }
??????? }
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3.問題來了，Android Framework是否也是一樣的原理呢？？猜測應該是一樣的才對，不然這個工具就沒有調試的價值了。
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我們來閱讀和分析framework中input event的相關代碼。
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我們從Kernel層往上看，先看看Framework中，直接操縱/dev/input設備的代碼。
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在.frameworks/base/libs/ui/EventHub.cpp 中，我們看到跟getevent工具類似的代碼。
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bool EventHub::getEvent(int32_t* outDeviceId, int32_t* outType,
??????? int32_t* outScancode, int32_t* outKeycode, uint32_t *outFlags,
??????? int32_t* outValue, nsecs_t* outWhen)
{
....
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??? while(1) {
....
??????? release_wake_lock(WAKE_LOCK_ID);
??????? pollres = poll(mFDs, mFDCount, -1);?
??????? acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
??????? if (pollres <= 0) {
??????????? if (errno != EINTR) {
??????????????? LOGW("select failed (errno=%d)/n", errno);
??????????????? usleep(100000);
??????????? }
??????????? continue;
??????? }
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....
??????? // mFDs[0] is used for inotify, so process regular events starting at mFDs[1]
??????? for(i = 1; i < mFDCount; i++) {
??????????? if(mFDs[i].revents) {
??????????????? LOGV("revents for %d = 0x%08x", i, mFDs[i].revents);
??????????????? if(mFDs[i].revents & POLLIN) {
??????????????????? res = read(mFDs[i].fd, &iev, sizeof(iev));?
??????????????????? if (res == sizeof(iev)) {
??????????????????????? LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d",
???????????????????????????? mDevices[i]->path.string(),
???????????? ....
??????? }
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4.那么framework中那個模塊再調用EventHub呢，接著往下查。
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在framework目錄中，輸入下面的命令查找
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# find . -name "*.cpp" |grep -v EventHub | xargs grep EventHub?
./base/services/jni/com_android_server_KeyInputQueue.cpp:#include <ui/EventHub.h>
./base/services/jni/com_android_server_KeyInputQueue.cpp:static sp<EventHub> gHub;
./base/services/jni/com_android_server_KeyInputQueue.cpp:??? sp<EventHub> hub = gHub;
./base/services/jni/com_android_server_KeyInputQueue.cpp:??????? hub = new EventHub;
./base/services/jni/com_android_server_KeyInputQueue.cpp:??? sp<EventHub> hub = gHub;
./base/services/jni/com_android_server_KeyInputQueue.cpp:??????? hub = new EventHub;
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5.從查找結果中得知，在jni文件com_android_server_KeyInputQueue.cpp文件中有對EventHub進行調用。
打開并閱讀com_android_server_KeyInputQueue.cpp文件得知，在下面的函數中調用了EventHub的getEvent函數
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static jboolean
android_server_KeyInputQueue_readEvent(JNIEnv* env, jobject clazz,
????????????????????????????????????????? jobject event)?
{
??? gLock.lock();
??? sp<EventHub> hub = gHub;
??? if (hub == NULL) {
??????? hub = new EventHub;
??????? gHub = hub;
??? }
??? gLock.unlock();
??? int32_t deviceId;
??? int32_t type;
??? int32_t scancode, keycode;
??? uint32_t flags;
??? int32_t value;
??? nsecs_t when;
??? bool res = hub->getEvent(&deviceId, &type, &scancode, &keycode,
??????????? &flags, &value, &when);?
??? env->SetIntField(event, gInputOffsets.mDeviceId, (jint)deviceId);
??? env->SetIntField(event, gInputOffsets.mType, (jint)type);
??? env->SetIntField(event, gInputOffsets.mScancode, (jint)scancode);
??? env->SetIntField(event, gInputOffsets.mKeycode, (jint)keycode);
??? env->SetIntField(event, gInputOffsets.mFlags, (jint)flags);
??? env->SetIntField(event, gInputOffsets.mValue, value);
??? env->SetLongField(event, gInputOffsets.mWhen,
??????????????????????? (jlong)(nanoseconds_to_milliseconds(when)));
??? return res;
}
6.根據jni的調用規則，在本文件中查找對于的java函數。
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static JNINativeMethod gInputMethods[] = {
??? /* name, signature, funcPtr */
??? { "readEvent",?????? "(Landroid/view/RawInputEvent;)Z",
??????????? (void*) android_server_KeyInputQueue_readEvent },
??? ....?
7. 接著順藤摸瓜，找到對應的java文件,base/services/java/com/android/server/KeyInputQueue.java
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??? private static native boolean readEvent(RawInputEvent outEvent);
在一個線程中會調用readEvent函數。
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??? Thread mThread = new Thread("InputDeviceReader") {
??????? public void run() {
??????????? if (DEBUG) Slog.v(TAG, "InputDeviceReader.run()");
??????????? android.os.Process.setThreadPriority(
??????????????????? android.os.Process.THREAD_PRIORITY_URGENT_DISPLAY);
??????????? RawInputEvent ev = new RawInputEvent();
??????????? while (true) {
??????????????? try {
??????????????????? InputDevice di;
??????????????????? // block, doesn't release the monitor
??????????????????? readEvent(ev);?
??????????????????? boolean send = false;
??????????????????? boolean configChanged = false;
??????????????????? if (false) {
??????????????????????? Slog.i(TAG, "Input event: dev=0x"
??????????????????????????????? + Integer.toHexString(ev.deviceId)
??????????????????????????????? + " type=0x" + Integer.toHexString(ev.type)
??????????????????????????????? + " scancode=" + ev.scancode
??????????????????????????????? + " keycode=" + ev.keycode
??????????????????????????????? + " value=" + ev.value);
??????????????????? }
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8.那是誰啟動這個線程呢？？？查找mThread變量，得知在KeyInputQueue的構造函數中會啟動這個線程。
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??? KeyInputQueue(Context context, HapticFeedbackCallback? hapticFeedbackCallback)?{
??????? if (MEASURE_LATENCY) {
??????????? lt = new LatencyTimer(100, 1000);
??????? }
??????? Resources r = context.getResources();
??????? BAD_TOUCH_HACK = r.getBoolean(com.android.internal.R.bool.config_filterTouchEvents);
??????? JUMPY_TOUCH_HACK = r.getBoolean(com.android.internal.R.bool.config_filterJumpyTouchEvents);
??????? mHapticFeedbackCallback = hapticFeedbackCallback;
??????? readExcludedDevices();
??????? PowerManager pm = (PowerManager)context.getSystemService(
??????????????????????????????????????????????????????? Context.POWER_SERVICE);
??????? mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
??????????????????????????????????????????????????????? "KeyInputQueue");
??????? mWakeLock.setReferenceCounted(false);
??????? mFirst = new QueuedEvent();
??????? mLast = new QueuedEvent();
??????? mFirst.next = mLast;
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??????? mThread.start();?
??? }
9.那這個KeyInputQueue是在哪里被實例化呢？
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而且查看KeyInputQueue類的聲明，得知它是一個abstract class.
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public abstract class KeyInputQueue
{
.....
}
說明它肯定會被某個類繼承.接著查找。
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/frameworks$ find . -name "*.java" |grep -v KeyInputQueue | xargs grep KeyInputQueue?
./policies/base/phone/com/android/internal/policy/impl/KeyguardViewMediator.java: * {@link com.android.server.KeyInputQueue}'s and {@link android.view.WindowManager}'s.
./base/services/java/com/android/server/PowerManagerService.java:??????????????????? && !"KeyInputQueue".equals(tag))) {
./base/services/java/com/android/server/WindowManagerService.java:import com.android.server.KeyInputQueue.QueuedEvent;
./base/services/java/com/android/server/WindowManagerService.java:??????? implements Watchdog.Monitor, KeyInputQueue.HapticFeedbackCallback {
./base/services/java/com/android/server/WindowManagerService.java:??????? return KeyInputQueue.getSwitchState(sw);
./base/services/java/com/android/server/WindowManagerService.java:??????? return KeyInputQueue.getSwitchState(devid, sw);
./base/services/java/com/android/server/WindowManagerService.java:??????? return KeyInputQueue.hasKeys(keycodes, keyExists);
./base/services/java/com/android/server/WindowManagerService.java:??? private class KeyQ extends KeyInputQueue
./base/services/java/com/android/server/WindowManagerService.java:??????????? implements KeyInputQueue.FilterCallback {
./base/services/java/com/android/server/InputDevice.java:??? // For use by KeyInputQueue for keeping track of the current touch
./base/services/java/com/android/server/InputDevice.java:??????????? if (KeyInputQueue.BAD_TOUCH_HACK) {
./base/services/java/com/android/server/InputDevice.java:??????????????????? Slog.i("KeyInputQueue", "Updating: " + currentMove);
./base/services/java/com/android/server/InputDevice.java:??????????????????? Slog.i("KeyInputQueue", "Updating: " + currentMove);
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10.從上面的查找結果得知，會在WindowManagerService.java中有一個KeyQ類繼承KeyInputQueue類，再在這個文件中查找KeyQ類在哪里定義并實例化的，找到在其構造函數里實例化的。
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?? private WindowManagerService(Context context, PowerManagerService pm,?
??????????? boolean haveInputMethods) {
??????? if (MEASURE_LATENCY) {
??????????? lt = new LatencyTimer(100, 1000);
??????? }
?????????? ....
??? mQueue = new KeyQ();?
??????? mInputThread = new InputDispatcherThread();
??????? PolicyThread thr = new PolicyThread(mPolicy, this, context, pm);
???????? ...
}
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至此，基本上把Input event的Framework的流程全部走完了。WindowManagerService是屬于System server進程里面起的一個Service.一開機就會運行，當然其構造函數一開機就能會運行。
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至此，整個流程如下：
?????????????? WindowManagerService
???????????????????????????? |
???????????????????????????? |
??????????????????????????? //
???????????????????????? KeyQ
???????????????????????????? |
???????????????????????????? |
??????????????????????????? //
??????????????????????? KeyInputQueue
???????????????????????????? |
???????????????????????????? |
??????????????????????????? //
??????????????????????? EventHub
???????????????????????????? |
???????????????????????????? |
??????????????????????????? //
???????????????????????? Kernel device (/dev/input)
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后續的文章將介紹/dev/input在Kernel中的實現。
轉載于:https://my.oschina.net/kings0527/blog/520703
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