Android 中input event的分析

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文章将分析Android 的Input Event 子系统的来龙去脉。

Android 系统里面有很多小工具，运行这些工具，我们对它们有一个感性的认识，进而阅读和分析这些小工具源代码，再顺藤摸瓜，就可以把整个子系统的来龙去脉弄清楚。

1.运行toolbox的getevent 工具。

# 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

运行这个工具，然后按键或者滑动触摸屏，会看到程序会实时打印event。从上面的输出来看，系统有5个input 子系统。它们分别是

add device 1: /dev/input/event4
name: "sensor-input"

#Sensor input 子系统

add device 2: /dev/input/event3
name: "88pm860x_hook"

#耳机Hook键子系统。可支持接电话挂电话的耳机上面有一个按键，对应的就是这个input 子系统。

add device 3: /dev/input/event2
name: "88pm860x_on"

#开机键 input 子系统
add device 4: /dev/input/event1
name: "88pm860x-touch"

#Touch Screen input 子系统

add device 5: /dev/input/event0
name: "pxa27x-keypad"

#按键子系统，包括Home/Menu/Back等按键。

可以尝试多种event，实际感觉一下出来的log。

2.阅读getevent的代码。代码为./core/toolbox/getevent.c

从代码中，我们知道，程序在while(1)的一个死循环里，不断地在读取 (select 操作)/dev/input 下面的文件，检查是否Kernel往里面更新内容，如果有内容更新，就把它打印出来。并且从代码中，我们还知道，任何一个event都有三种属性，type,code,value.

    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;
                }
            }
        }

3.问题来了，Android Framework是否也是一样的原理呢？？猜测应该是一样的才对，不然这个工具就没有调试的价值了。

我们来阅读和分析framework中input event的相关代码。

我们从Kernel层往上看，先看看Framework中，直接操纵/dev/input设备的代码。

在.frameworks/base/libs/ui/EventHub.cpp 中，我们看到跟getevent工具类似的代码。

bool EventHub::getEvent(int32_t* outDeviceId, int32_t* outType,
int32_t* outScancode, int32_t* outKeycode, uint32_t *outFlags,
int32_t* outValue, nsecs_t* outWhen)
{

....

    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;
        }

....

        // 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(),

....

}

4.那么framework中那个模块再调用EventHub呢，接着往下查。

在framework目录中，输入下面的命令查找

# 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;

5.从查找结果中得知，在jni文件com_android_server_KeyInputQueue.cpp文件中有对EventHub进行调用。

打开并阅读com_android_server_KeyInputQueue.cpp文件得知，在下面的函数中调用了EventHub的getEvent函数

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.根据jni的调用规则，在本文件中查找对于的java函数。

static JNINativeMethod gInputMethods[] = {

    /* name, signature, funcPtr */
    { "readEvent",       "(Landroid/view/RawInputEvent;)Z",
            (void*) android_server_KeyInputQueue_readEvent },

....

7. 接着顺藤摸瓜，找到对应的java文件,base/services/java/com/android/server/KeyInputQueue.java

private static native boolean readEvent(RawInputEvent outEvent);

在一个线程中会调用readEvent函数。

    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);
                    }

8.那是谁启动这个线程呢？？？查找mThread变量，得知在KeyInputQueue的构造函数中会启动这个线程。

    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;

mThread.start();
}

9.那这个KeyInputQueue是在哪里被实例化呢？

而且查看KeyInputQueue类的声明，得知它是一个abstract class.

public abstract class KeyInputQueue

{

.....

}

说明它肯定会被某个类继承.接着查找。

/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);

10.从上面的查找结果得知，会在WindowManagerService.java中有一个KeyQ类继承KeyInputQueue类，再在这个文件中查找KeyQ类在哪里定义并实例化的，找到在其构造函数里实例化的。

   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);
         ...

}

至此，基本上把Input event的Framework的流程全部走完了。WindowManagerService是属于System server进程里面起的一个Service.一开机就会运行，当然其构造函数一开机就能会运行。

至此，整个流程如下：

WindowManagerService

KeyQ

KeyInputQueue

EventHub

Kernel device (/dev/input)

后续的文章将介绍/dev/input在Kernel中的实现