Analyze the Process of Setting KL for Physical Keyboard

基于Android 8.0源码，分析InputManagerService给Physical Keyboard 设置Keyboard Layout(KL)的具体过程。

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frameworks/native/services/inputflinger/
  - InputDispatcher.cpp
  - InputReader.cpp
  - InputManager.cpp
  - EventHub.cpp
  - InputListener.cpp

frameworks/native/libs/input/
  - InputTransport.cpp
  - Input.cpp
  - InputDevice.cpp
  - Keyboard.cpp
  - KeyCharacterMap.cpp
  - IInputFlinger.cpp

frameworks/base/services/core/
  - java/com/android/server/input/InputManagerService.java
  - java/com/android/server/input/PersistentDataStore.java
  - jni/com_android_server_input_InputManagerService.cpp

frameworks/base/packages/InputDevices/
  - src/com/android/inputdevices/InputDeviceReceiver.java
  - res/xml/keyboard_layouts.xml
  - res/raw/...

1. 概述

Gityuan博客有详细分析Input系统，从该博客可以学习到Input模块的工作原理， 以及主要组成：

  • Native层的InputReader负责从EventHub取出事件并处理，再交给InputDispatcher
  • Native层的InputDispatcher接收来自InputReader的输入事件，并记录WMS的窗口信息，用于派发事件到合适的窗口
  • Java层的InputManagerService跟WMS交互，WMS记录所有窗口信息，并同步更新到IMS，为InputDispatcher正确派发事件到ViewRootImpl提供保障

当Physical Keyboard(后面会直接用PK代替) 通过USB与Android设备连接时，首先触发的是硬件驱动，UsbHostManager 识别PK并发出USB_DEVICE_ATTACHED广播, EventHub通过InputReader线程会循环读取消息并调用getEvents()读取输入事件。
调用的流程是：

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EventHub::getEvents -> EventHub::scanDevicesLocked -> EventHub::scanDirLocked -> EventHub::openDeviceLocked

查看openDeviceLocked方法，可以知道此方法首先打开devicePath，然后new Device，调用LoadKeyMapLocked()来给PK load相应的.kl和.kcm, 所有的.kl文件和.kcm文件都放在/framework/base/data/keyboards/下面。我们可以看到有许多Vendor_XXXX_PRODUCT_XXXX命名的.kl和.kcm file，在loadKeymap时就是根据Device的vendor， product值来查找有没有相对应的Vendor_XXXX_PRODUCT_XXXX文件。多数情况下都不会有与PK对应的.kl和.kcm文件，这时Input系统会load默认的Generic.kl和Generic.kcm给该PK (Generic用的是qwerty layout)。

这也就是为什么有一些法语键盘或者德语键盘链接Android设备之后还是英语的layout的原因。
详细的调用流程可以看源码或者是这篇博文https://blog.csdn.net/kc58236582/.

以上简单介绍了Input系统处理PK连接事件的过程和为其设置.kl和.kcm文件的过程。接下来我将详细介绍一下重新给PK设置Keyboard lauout的过程还有重载新的layout的过程。

2. 为PK重置kl

如上所述，当我们用到非英语键盘时，layout还会加载成qwert的，面对这个问题Input系统已经提供了相应的function供开发者调用：

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/frameworks/base/services/java/com/android/server/input/InputManagerService.java
    @Override
    public void setKeyboardLayoutForInputDevice(InputDeviceIdentifier identifier,
            InputMethodInfo imeInfo, InputMethodSubtype imeSubtype,
            String keyboardLayoutDescriptor) {
        if (!checkCallingPermission(android.Manifest.permission.SET_KEYBOARD_LAYOUT,
                "setKeyboardLayoutForInputDevice()")) {
            throw new SecurityException("Requires SET_KEYBOARD_LAYOUT permission");
        }
        if (keyboardLayoutDescriptor == null) {
            throw new IllegalArgumentException("keyboardLayoutDescriptor must not be null");
        }
        if (imeInfo == null) {
            throw new IllegalArgumentException("imeInfo must not be null");
        }
        InputMethodSubtypeHandle handle = new InputMethodSubtypeHandle(imeInfo, imeSubtype);
        setKeyboardLayoutForInputDeviceInner(identifier, handle, keyboardLayoutDescriptor);
    }
    private void setKeyboardLayoutForInputDeviceInner(InputDeviceIdentifier identifier,
            InputMethodSubtypeHandle imeHandle, String keyboardLayoutDescriptor) {
        String key = getLayoutDescriptor(identifier);
        synchronized (mDataStore) {
            try {
                if (mDataStore.setKeyboardLayout(key, imeHandle, keyboardLayoutDescriptor)) { (见2.2.1)
                    if (DEBUG) {
                        Slog.d(TAG, "Set keyboard layout " + keyboardLayoutDescriptor +
                                " for subtype " + imeHandle + " and device " + identifier +
                                " using key " + key);
                    }
                    if (imeHandle.equals(mCurrentImeHandle)) {
                        if (DEBUG) {
                            Slog.d(TAG, "Layout for current subtype changed, switching layout");
                        }
                        SomeArgs args = SomeArgs.obtain();
                        args.arg1 = identifier;
                        args.arg2 = imeHandle;
                        mHandler.obtainMessage(MSG_SWITCH_KEYBOARD_LAYOUT, args).sendToTarget();（见2.2.3）
                    }
                    mHandler.sendEmptyMessage(MSG_RELOAD_KEYBOARD_LAYOUTS);
                }
            } finally {
                mDataStore.saveIfNeeded();
            }
        }
    }

此方法被用在Settings/inputmethod里.
下面我们分析Input系统是如何在底层运作的。

2.1 InputDevices

2.1.1 InputDeviceReceiver

这个package维护的是一个接收“QUERY_KEYBOARD_LAYOUTS”的BroadcastReceiver。

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/src/com/android/inputdevices/InputDeviceReceiver.java
        <receiver android:name=".InputDeviceReceiver"
                android:label="@string/keyboard_layouts_label">
            <intent-filter>
                <action android:name="android.hardware.input.action.QUERY_KEYBOARD_LAYOUTS" />
            </intent-filter>
            <meta-data android:name="android.hardware.input.metadata.KEYBOARD_LAYOUTS"
                    android:resource="@xml/keyboard_layouts" />
        </receiver>

2.1.2 Keyboardlayouts

这里还存放了重要的/res/xml/keyboardlayouts.xml 和 /res/raw/…kcm, /res/raw/下存放了所有语言的.kcm files. xml文件是map所有.kcm文件用的。

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<?xml version="1.0" encoding="utf-8"?>
<keyboard-layouts xmlns:android="http://schemas.android.com/apk/res/android">
    <keyboard-layout android:name="keyboard_layout_english_uk"
            android:label="@string/keyboard_layout_english_uk_label"
            android:keyboardLayout="@raw/keyboard_layout_english_uk" />
...
    <keyboard-layout android:name="keyboard_layout_latvian"
            android:label="@string/keyboard_layout_latvian"
            android:keyboardLayout="@raw/keyboard_layout_latvian_qwerty" />
</keyboard-layouts>

2.2 InputManagerService

此章节将介绍IMS中重要的方法和相应的Class。

2.2.1 PersistentDataStore

IMS通过PersistentDataStore来存储所有的Input devices的信息。在/data/system/input-manager-state.xml中。
通过adb可以查看该文件：

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/data/system # cat input-manager-state.xml                                                                                                                      <?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<input-manager-state>
    <input-devices>
        <input-device descriptor="vendor:16700,product:8467">
            <keyboard-layout descriptor="com.android.inputdevices/com.android.inputdevices.InputDeviceReceiver/keyboard_layout_french" input-method-id="com.google.android.inputmethod.latin/com.android.inputmethod.latin.LatinIME" input-method-subtype-id="843948332" current="true" />
        </input-device>
        <input-device descriptor="vendor:1266,product:1027">
            <keyboard-layout descriptor="com.android.inputdevices/com.android.inputdevices.InputDeviceReceiver/keyboard_layout_french" input-method-id="com.google.android.inputmethod.latin/com.android.inputmethod.latin.LatinIME" input-method-subtype-id="-921088104" current="true" />
        </input-device>
    </input-devices>
</input-manager-state>

我们可以看到其中com.android.inputdevices.InputDeviceReceiver/keyboard_layout_french就是对应着2.1.2中的Keyboard-layout name.

IMS.mDataStore就是PersistentDataStore的实例，以上IMS +1391行code就是在set相应的layout值。

2.2.2 visitAllKeyboardLayouts()

这个方法会被native层用到，之后的篇幅会介绍到。此方法主要功能就是遍历2.1.2中的keyboardlayouts.xml维护的所有的layouts。
还有另外一个方法是visitKeyboardLayout()会被Settings.getKeyboardLayout()用到，原理也是一样的，遍历xml找到相应的layout。
具体实现是如下：

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private void visitAllKeyboardLayouts(KeyboardLayoutVisitor visitor) {
    final PackageManager pm = mContext.getPackageManager();
    Intent intent = new Intent(InputManager.ACTION_QUERY_KEYBOARD_LAYOUTS);
    for (ResolveInfo resolveInfo : pm.queryBroadcastReceivers(intent,
            PackageManager.GET_META_DATA | PackageManager.MATCH_DIRECT_BOOT_AWARE
                    | PackageManager.MATCH_DIRECT_BOOT_UNAWARE)) {
        final ActivityInfo activityInfo = resolveInfo.activityInfo;
        final int priority = resolveInfo.priority;
        visitKeyboardLayoutsInPackage(pm, activityInfo, null, priority, visitor);
    }
}

其中InputManager.ACTION_QUERY_KEYBOARD_LAYOUTS 就是2.1.1中的QUERY_KEYBOARD_LAYOUTS。

2.2.3 handleSwithKeyboardLayout

此方法就是handle IMS +1404行的MSG_SWITCH_KEYBOARD_LAYOUT message。它主要做了两件事：

  • mDataStore.switchKeyboardLayout, 将input-manager-state.xml更新为之前setKeyboardLayout(IMS +1391行)的值。
  • reloadKeyboardLayouts() -> nativeReloadKeyboardLayouts() 见2.3.1

2.3 Native InputManager

2.3.1 nativeReloadKeyboardLayouts

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/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
static void nativeReloadKeyboardLayouts(JNIEnv* /* env */,
        jclass /* clazz */, jlong ptr) {
    NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);

    im->getInputManager()->getReader()->requestRefreshConfiguration(
            InputReaderConfiguration::CHANGE_KEYBOARD_LAYOUTS);
}

主要工作是trigger InputReader::requestRefreshConfiguration()

2.3.2 InputReader.cpp

gityuan的一篇博客中清晰地介绍了InputReader, 对理解下面的代码会很有帮助。

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void InputReader::requestRefreshConfiguration(uint32_t changes) {
    AutoMutex _l(mLock);

    if (changes) {
        bool needWake = !mConfigurationChangesToRefresh;
        mConfigurationChangesToRefresh |= changes;

        if (needWake) {
            mEventHub->wake();
        }
    }
}
...
void InputReader::loopOnce() {
    int32_t oldGeneration;
    int32_t timeoutMillis;
    bool inputDevicesChanged = false;
    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
...
}
...
void InputReader::refreshConfigurationLocked(uint32_t changes) {
    mPolicy->getReaderConfiguration(&mConfig);
    mEventHub->setExcludedDevices(mConfig.excludedDeviceNames);

    if (changes) {
...
        if (changes & InputReaderConfiguration::CHANGE_MUST_REOPEN) {
            mEventHub->requestReopenDevices();
        } else {
            for (size_t i = 0; i < mDevices.size(); i++) {
                InputDevice* device = mDevices.valueAt(i);
                device->configure(now, &mConfig, changes);
            }
        }
    }
}
...
void InputDevice::configure(nsecs_t when, const InputReaderConfiguration* config, uint32_t changes) {
...
    if (!isIgnored()) {
        if (!changes) { // first time only
            mContext->getEventHub()->getConfiguration(mId, &mConfiguration);
        }

        if (!changes || (changes & InputReaderConfiguration::CHANGE_KEYBOARD_LAYOUTS)) {
            if (!(mClasses & INPUT_DEVICE_CLASS_VIRTUAL)) {
                sp<KeyCharacterMap> keyboardLayout =
                        mContext->getPolicy()->getKeyboardLayoutOverlay(mIdentifier); (见2.4)
                if (mContext->getEventHub()->setKeyboardLayoutOverlay(mId, keyboardLayout)) {
                    bumpGeneration();（见2.5）
                }
            }
        }
...
}

这部分的代码主要工作是

  • 把InputReaderConfiguration::CHANGE_KEYBOARD_LAYOUTS换位给
    mConfigurationChangesToRefresh
  • InputReader线程不停的loop，当mConfigurationChangesToRefresh不为0时，调用refreshConfigurationLocked方法
  • 当changes值不为CHANGE_MUST_REOPEN时，将循环所有的InputDevice，并调用configure方法
  • 当changes是CHANGE_KEYBOARD_LAYOUTS时 会调用两个重要的方法，将会再下两个小节详细介绍

2.4 getPolicy()

如Gityuan博客中提到的，InputReader的成员变量mPolicy都是指NativeInputManager对象。这里getPolicy()得到的就是NativeInputManager对象。接下来我们看一下getKeyboardLayoutOverlay方法的具体工作。

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/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
public:
    NativeInputManager(jobject contextObj, jobject serviceObj, const sp<Looper>& looper);
...
    /* --- InputReaderPolicyInterface implementation --- */
...
    virtual sp<KeyCharacterMap> getKeyboardLayoutOverlay(const InputDeviceIdentifier& identifier);
...
int register_android_server_InputManager(JNIEnv* env) {
    int res = jniRegisterNativeMethods(env, "com/android/server/input/InputManagerService",
            gInputManagerMethods, NELEM(gInputManagerMethods));
    (void) res;  // Faked use when LOG_NDEBUG.
    LOG_FATAL_IF(res < 0, "Unable to register native methods.");

    // Callbacks

    jclass clazz;
    FIND_CLASS(clazz, "com/android/server/input/InputManagerService");
...
    GET_METHOD_ID(gServiceClassInfo.getKeyboardLayoutOverlay, clazz,
            "getKeyboardLayoutOverlay",
            "(Landroid/hardware/input/InputDeviceIdentifier;)[Ljava/lang/String;");

主要工作就是通过JNI调用JAVA层的InputManagerService.getKeyboardLayoutOverlay()方法。代码如下：

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    // Native callback.
    private String[] getKeyboardLayoutOverlay(InputDeviceIdentifier identifier) {
        if (!mSystemReady) {
            return null;
        }

        String keyboardLayoutDescriptor = getCurrentKeyboardLayoutForInputDevice(identifier);
        if (keyboardLayoutDescriptor == null) {
            return null;
        }

        final String[] result = new String[2];
        visitKeyboardLayout(keyboardLayoutDescriptor, new KeyboardLayoutVisitor() {
            @Override
            public void visitKeyboardLayout(Resources resources,
                    int keyboardLayoutResId, KeyboardLayout layout) {
                try {
                    result[0] = layout.getDescriptor();
                    result[1] = Streams.readFully(new InputStreamReader(
                            resources.openRawResource(keyboardLayoutResId)));
                } catch (IOException ex) {
                } catch (NotFoundException ex) {
                }
            }
        });
...
    }

可以看到它的主要工作是

  • 从InputDeviceIdentifier中拿到keyboardLayoutDescriptor
  • 调用visitKeyboardLayout()去遍历kayboardlayouts.xml找到对应的layout resource文件并返回。见2.2.2。

2.5 EventHub::setKeyboardLayoutOverlay()

从2.4节得到的keyboardlayout result作为参数，通过EventHub设置给相应的Device。

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bool EventHub::setKeyboardLayoutOverlay(int32_t deviceId,
        const sp<KeyCharacterMap>& map) {
    AutoMutex _l(mLock);
    Device* device = getDeviceLocked(deviceId);
    if (device) {
        if (map != device->overlayKeyMap) {
            device->overlayKeyMap = map;
            device->combinedKeyMap = KeyCharacterMap::combine(
                    device->keyMap.keyCharacterMap, map);
            return true;
        }
    }
    return false;
}

最终实现为PK设置非英语的keyboard layout。

3. 总结

Native callback 感觉是最有意思的地方，以后可以用一下，JNI层还是需要多加研究的。对于Input系统，算是通过这次机会了解到这么多细节的东西，但是还有InputDispatch的部分还需要日后仔细学习。

ESC