映射表基本概念

由于Android调用getEvents得到的key是linux发送过来的scan code，而Android处理的是类似于KEY_UP这种统一类型的key code，因此需要有映射表把scan code转换成key code。映射表在板子上的位置是/system/usr/keylayout/xxx.kl，先看一下映射表是什么样子的，下面截选了一段。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 key 2 1 key 3 2 key 4 3 key 5 4 key 6 5 key 7 6 key 8 7 key 9 8 key 10 9 key 11 0 key 28 DPAD_CENTER key 102 HOME key 103 DPAD_UP WAKE_DROPPED key 105 DPAD_LEFT WAKE_DROPPED key 106 DPAD_RIGHT WAKE_DROPPED key 108 DPAD_DOWN WAKE_DROPPED key 111 DEL key 113 VOLUME_MUTE key 114 VOLUME_DOWN key 115 VOLUME_UP key 116 POWER

可以看到每行都是一个映射项，映射项格式如下：

key [scan code] [key label] [flag label] [flag label] ...

key是关键字，表明这个映射项是作为键值映射
scan code是从linux device取得的键值
key label是把scan code映射到key code中间的关键字，通过该关键字可以得到key code。
flag label即按键的标记的关键字，通过flag label可以得到flag，一行映射项后面可以有多个flag label

从3和4可以知道，还有一个key label到key code的过程，以及flag label到flag的过程

另外，映射表是设备相关的。由于不同设备发送到Android的scan code可能会不同，因此每个设备需要用自身对应的映射表才能正确解析出key code。

映射表加载过程

1. 获取设备相关信息

在构造EventHub的时候，就决定了需要扫描输入设备。然后会在第一次getEvents进行一次扫描。

扫描输入设备主要有两个目的：

得到该设备的各种信息，如：设备名称，设备版本，设备产品码等，这些信息都可以作为该设备的标识。
知道该设备所发送事件的类型，如：按键事件，触控事件，滑动事件，开关事件，xy坐标等；通过所发送事件的类型，就能定位出设备的类型。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 EventHub::EventHub( void ) : mNeedToScanDevices( true ), {...} size_t EventHub::getEvents( int timeoutMillis, RawEvent* buffer, size_t bufferSize) { if (mNeedToScanDevices) { mNeedToScanDevices = false ; scanDevicesLocked(); mNeedToSendFinishedDeviceScan = true ; } } void EventHub::scanDevicesLocked() { status_t res = scanDirLocked(DEVICE_PATH); if (res < 0) { ALOGE( "scan dir failed for %s\n" , DEVICE_PATH); } if (mDevices.indexOfKey(VIRTUAL_KEYBOARD_ID) < 0) { createVirtualKeyboardLocked(); } }

扫描的目录是/dev/input，linux中每加入一个输入设备，都会在该目录下创建设备文件。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 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; }

在openDeviceLocked中就能清晰分析出扫描设备的两个目的

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 status_t EventHub::openDeviceLocked( const char *devicePath) { int fd = open(devicePath, O_RDWR | O_CLOEXEC); // Get device name. if (ioctl(fd, EVIOCGNAME( sizeof (buffer) - 1), &buffer) < 1) { //fprintf(stderr, "could not get device name for %s, %s\n", devicePath, strerror(errno)); } else { buffer[ sizeof (buffer) - 1] = '\0' ; identifier.name.setTo(buffer); } // Get device driver version. int driverVersion; if (ioctl(fd, EVIOCGVERSION, &driverVersion)) { ALOGE( "could not get driver version for %s, %s\n" , devicePath, strerror ( errno )); close(fd); return -1; } struct input_id inputId; if (ioctl(fd, EVIOCGID, &inputId)) { ALOGE( "could not get device input id for %s, %s\n" , devicePath, strerror ( errno )); close(fd); return -1; } identifier.bus = inputId.bustype; identifier.product = inputId.product; identifier.vendor = inputId.vendor; identifier.version = inputId.version; ... Device* device = new Device(fd, deviceId, String8(devicePath), identifier); // Figure out the kinds of events the device reports. ioctl(fd, EVIOCGBIT(EV_KEY, sizeof (device->keyBitmask)), device->keyBitmask); ioctl(fd, EVIOCGBIT(EV_ABS, sizeof (device->absBitmask)), device->absBitmask); ioctl(fd, EVIOCGBIT(EV_REL, sizeof (device->relBitmask)), device->relBitmask); ioctl(fd, EVIOCGBIT(EV_SW, sizeof (device->swBitmask)), device->swBitmask); ioctl(fd, EVIOCGBIT(EV_LED, sizeof (device->ledBitmask)), device->ledBitmask); ioctl(fd, EVIOCGBIT(EV_FF, sizeof (device->ffBitmask)), device->ffBitmask); ioctl(fd, EVIOCGPROP( sizeof (device->propBitmask)), device->propBitmask); //mouse device? if (test_bit(BTN_MOUSE, device->keyBitmask) && test_bit(REL_X, device->relBitmask) && test_bit(REL_Y, device->relBitmask)) { device->classes |= INPUT_DEVICE_CLASS_CURSOR; } // See if this is a touch pad. // Is this a new modern multi-touch driver? if (test_bit(ABS_MT_POSITION_X, device->absBitmask) && test_bit(ABS_MT_POSITION_Y, device->absBitmask)) { // Some joysticks such as the PS3 controller report axes that conflict // with the ABS_MT range. Try to confirm that the device really is // a touch screen. if (test_bit(BTN_TOUCH, device->keyBitmask) || !haveGamepadButtons) { device->classes |= INPUT_DEVICE_CLASS_TOUCH | INPUT_DEVICE_CLASS_TOUCH_MT; } // Is this an old style single-touch driver? } else if (test_bit(BTN_TOUCH, device->keyBitmask) && test_bit(ABS_X, device->absBitmask) && test_bit(ABS_Y, device->absBitmask)) { device->classes |= INPUT_DEVICE_CLASS_TOUCH; } // See if this device is a joystick. // Assumes that joysticks always have gamepad buttons in order to distinguish them // from other devices such as accelerometers that also have absolute axes. if (haveGamepadButtons) { uint32_t assumedClasses = device->classes | INPUT_DEVICE_CLASS_JOYSTICK; for ( int i = 0; i <= ABS_MAX; i++) { if (test_bit(i, device->absBitmask) && (getAbsAxisUsage(i, assumedClasses) & INPUT_DEVICE_CLASS_JOYSTICK)) { device->classes = assumedClasses; break ; } } } ... }

2. 加载映射表

通过设备信息与设备类型，我们就能去加载正确的映射表了

1 2 3 4 5 6 7 8 9 10 status_t EventHub::openDeviceLocked( const char *devicePath) { ... if (device->classes & (INPUT_DEVICE_CLASS_KEYBOARD | INPUT_DEVICE_CLASS_JOYSTICK)) { // Load the keymap for the device. keyMapStatus = loadKeyMapLocked(device); } ... }

1 2 3 status_t EventHub::loadKeyMapLocked(Device* device) { return device->keyMap.load(device->identifier, device->configuration); }

加载配置文件分为下面几个步骤

1. 通过设备的配置文件去加载配置文件内制定好的映射表

2. 如果1不成功则通过设备信息加载对应的映射表

3. 如果2不成功则加载通用映射表

4. 如果3不成功则加载虚拟映射表

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 status_t KeyMap::load( const InputDeviceIdentifier& deviceIdenfifier, const PropertyMap* deviceConfiguration) { // Use the configured key layout if available. if (deviceConfiguration) { String8 keyLayoutName; if (deviceConfiguration->tryGetProperty(String8( "keyboard.layout" ), keyLayoutName)) { status_t status = loadKeyLayout(deviceIdenfifier, keyLayoutName); if (status == NAME_NOT_FOUND) { ALOGE( "Configuration for keyboard device '%s' requested keyboard layout '%s' but " "it was not found." , deviceIdenfifier.name.string(), keyLayoutName.string()); } } String8 keyCharacterMapName; if (deviceConfiguration->tryGetProperty(String8( "keyboard.characterMap" ), keyCharacterMapName)) { status_t status = loadKeyCharacterMap(deviceIdenfifier, keyCharacterMapName); if (status == NAME_NOT_FOUND) { ALOGE( "Configuration for keyboard device '%s' requested keyboard character " "map '%s' but it was not found." , deviceIdenfifier.name.string(), keyLayoutName.string()); } } if (isComplete()) { return OK; } } // Try searching by device identifier. if (probeKeyMap(deviceIdenfifier, String8::empty())) { return OK; } // Fall back on the Generic key map. // TODO Apply some additional heuristics here to figure out what kind of // generic key map to use (US English, etc.) for typical external keyboards. if (probeKeyMap(deviceIdenfifier, String8( "Generic" ))) { return OK; } // Try the Virtual key map as a last resort. if (probeKeyMap(deviceIdenfifier, String8( "Virtual" ))) { return OK; } // Give up! ALOGE( "Could not determine key map for device '%s' and no default key maps were found!" , deviceIdenfifier.name.string()); return NAME_NOT_FOUND; }

一般的情况我们会走第2步，因此从probeKeyMap往下分析

1 2 3 4 5 6 7 8 9 10 bool KeyMap::probeKeyMap( const InputDeviceIdentifier& deviceIdentifier, const String8& keyMapName) { if (!haveKeyLayout()) { loadKeyLayout(deviceIdentifier, keyMapName); } if (!haveKeyCharacterMap()) { loadKeyCharacterMap(deviceIdentifier, keyMapName); } return isComplete(); }

对于按键，有键盘按键与自定义按键两种，两者加载的文件后缀不同。键盘按键的映射表后缀是.kcm，而自定义按键映射表后缀是.kl。另外两者映射表的格式也不同，我们这里以自定义按键映射表为例，其中有三个步骤：

获取映射表文件路径
加载映射表文件
如果加载映射表文件成功的话，设置该路径为当前设备的自定义映射文件路径。（否则会去解析Generic.kl或者virtual.kl）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 status_t KeyMap::loadKeyLayout( const InputDeviceIdentifier& deviceIdentifier, const String8& name) { String8 path(getPath(deviceIdentifier, name, INPUT_DEVICE_CONFIGURATION_FILE_TYPE_KEY_LAYOUT)); if (path.isEmpty()) { return NAME_NOT_FOUND; } status_t status = KeyLayoutMap::load(path, &keyLayoutMap); if (status) { return status; } keyLayoutFile.setTo(path); return OK; }

1. 获取映射表文件路径

我们从加载映射表文件的步骤2进来，那传入的name为空，则调用到getInputDeviceConfigurationFilePathByDeviceIdentifier，即通过设备标识来产生路径

1 2 3 4 5 6 String8 KeyMap::getPath( const InputDeviceIdentifier& deviceIdentifier, const String8& name, InputDeviceConfigurationFileType type) { return name.isEmpty() ? getInputDeviceConfigurationFilePathByDeviceIdentifier(deviceIdentifier, type) : getInputDeviceConfigurationFilePathByName(name, type); }

如果设备标识中的vendor，product，version都不为0的话，表明可以通过这些信息来组合成一个字符串，这个字符串就是映射表文件的前缀，否则，会设备名称deviceIdentifier.name就是映射表文件的前缀。后缀通过type指定。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 String8 getInputDeviceConfigurationFilePathByDeviceIdentifier( const InputDeviceIdentifier& deviceIdentifier, InputDeviceConfigurationFileType type) { if (deviceIdentifier.vendor !=0 && deviceIdentifier.product != 0) { if (deviceIdentifier.version != 0) { // Try vendor product version. String8 versionPath(getInputDeviceConfigurationFilePathByName( String8::format( "Vendor_%04x_Product_%04x_Version_%04x" , deviceIdentifier.vendor, deviceIdentifier.product, deviceIdentifier.version), type)); if (!versionPath.isEmpty()) { return versionPath; } } // Try vendor product. String8 productPath(getInputDeviceConfigurationFilePathByName( String8::format( "Vendor_%04x_Product_%04x" , deviceIdentifier.vendor, deviceIdentifier.product), type)); if (!productPath.isEmpty()) { return productPath; } } // Try device name. return getInputDeviceConfigurationFilePathByName(deviceIdentifier.name, type); }

假设当前设备的设备名称是input_ir，传入的type是INPUT_DEVICE_CONFIGURATION_FILE_TYPE_KEY_LAYOUT，则设备的文件名为input_ir.kl

2.加载映射表文件

加载映射表文件最终目的是解析该文件得到映射表，其中也分为三个步骤：

打开映射表文件
创建映射表
解析映射表文件并把映射项加入映射表

1 2 3 4 5 6 7 8 9 10 status_t KeyLayoutMap::load( const String8& filename, sp<KeyLayoutMap>* outMap) { status_t status = Tokenizer::open(filename, &tokenizer); sp<KeyLayoutMap> map = new KeyLayoutMap(); Parser parser(map.get(), tokenizer); status = parser.parse(); }

我们直接看最重要的解析部分

parse函数是一个while循环，一行一行地解析映射表项

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 status_t KeyLayoutMap::Parser::parse() { while (!mTokenizer->isEof()) { mTokenizer->skipDelimiters(WHITESPACE); if (!mTokenizer->isEol() && mTokenizer->peekChar() != '#' ) { String8 keywordToken = mTokenizer->nextToken(WHITESPACE); if (keywordToken == "key" ) { mTokenizer->skipDelimiters(WHITESPACE); status_t status = parseKey(); if (status) return status; } else if (keywordToken == "axis" ) { mTokenizer->skipDelimiters(WHITESPACE); status_t status = parseAxis(); if (status) return status; } else { ALOGE( "%s: Expected keyword, got '%s'." , mTokenizer->getLocation().string(), keywordToken.string()); return BAD_VALUE; } mTokenizer->skipDelimiters(WHITESPACE); if (!mTokenizer->isEol() && mTokenizer->peekChar() != '#' ) { ALOGE( "%s: Expected end of line or trailing comment, got '%s'." , mTokenizer->getLocation().string(), mTokenizer->peekRemainderOfLine().string()); return BAD_VALUE; } } mTokenizer->nextLine(); } return NO_ERROR; }

每一行的解析步骤如下：

跳过行首的空格符
如果开头第一个字符是”#”，跳过当前行
如果开头的关键词是key，跳过空白分割符，调用parseKey解析，如果解析出错则返回错误
如果开头的关键词是axis，跳过空白分隔符，调用parseAxis解析，如果解析出错则返回错误
如果开头的关键词是其他的词，说明这个映射表文件有误，返回错误
跳过行末的空格符
如果行末还有”#”以外的字符，说明这个映射表文件有误，返回错误

下面以parseKey为例，分析它是怎么解析出scan code与key code的（由于我们没用到usage code，所以忽略usage，直接分析scan code流程）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 status_t KeyLayoutMap::Parser::parseKey() { String8 codeToken = mTokenizer->nextToken(WHITESPACE); //scan code从字符串转换成数字 int32_t code = int32_t( strtol (codeToken.string(), &end, 0)); if (*end) { return BAD_VALUE; } //我们用的是scan code KeyedVector<int32_t, Key>& map = mapUsage ? mMap->mKeysByUsageCode : mMap->mKeysByScanCode; //如果有重复的scan code，会出错返回 if (map.indexOfKey(code) >= 0) { ALOGE( "%s: Duplicate entry for key %s '%s'." , mTokenizer->getLocation().string(), mapUsage ? "usage" : "scan code" , codeToken.string()); return BAD_VALUE; } mTokenizer->skipDelimiters(WHITESPACE); String8 keyCodeToken = mTokenizer->nextToken(WHITESPACE); //通过label获取key code int32_t keyCode = getKeyCodeByLabel(keyCodeToken.string()); if (!keyCode) { ALOGE( "%s: Expected key code label, got '%s'." , mTokenizer->getLocation().string(), keyCodeToken.string()); return BAD_VALUE; } //key label后可以接flag，flag从getKeyFlagByLabel解析 uint32_t flags = 0; for (;;) { mTokenizer->skipDelimiters(WHITESPACE); if (mTokenizer->isEol() || mTokenizer->peekChar() == '#' ) break ; String8 flagToken = mTokenizer->nextToken(WHITESPACE); uint32_t flag = getKeyFlagByLabel(flagToken.string()); if (!flag) { ALOGE( "%s: Expected key flag label, got '%s'." , mTokenizer->getLocation().string(), flagToken.string()); return BAD_VALUE; } if (flags & flag) { ALOGE( "%s: Duplicate key flag '%s'." , mTokenizer->getLocation().string(), flagToken.string()); return BAD_VALUE; } flags |= flag; } Key key;

Android输入系统（三）：加载按键映射