函数首先根据文件名来打开这个设备文件：
- fd = open(deviceName, O_RDWR);
系统中所有输入设备文件信息都保存在成员变量mDevicesById中，因此，先在mDevicesById找到一个空位置来保存当前打开的设备文件信息：
- mDevicesById[devid].seq = (mDevicesById[devid].seq+(1<<SEQ_SHIFT))&SEQ_MASK;
- if (mDevicesById[devid].seq == 0) {
- mDevicesById[devid].seq = 1<<SEQ_SHIFT;
- }
找到了空闲位置后，就为这个输入设备文件创建相应的device_t信息：
- mDevicesById[devid].seq = (mDevicesById[devid].seq+(1<<SEQ_SHIFT))&SEQ_MASK;
- if (mDevicesById[devid].seq == 0) {
- mDevicesById[devid].seq = 1<<SEQ_SHIFT;
- }
- new_mFDs = (pollfd*)realloc(mFDs, sizeof(mFDs[0]) * (mFDCount + 1));
- new_devices = (device_t**)realloc(mDevices, sizeof(mDevices[0]) * (mFDCount + 1));
- if (new_mFDs == NULL || new_devices == NULL) {
- LOGE("out of memory");
- return -1;
- }
- mFDs = new_mFDs;
- mDevices = new_devices;
- ......
- device_t* device = new device_t(devid|mDevicesById[devid].seq, deviceName, name);
- if (device == NULL) {
- LOGE("out of memory");
- return -1;
- }
- device->fd = fd;
同时，这个设备文件还会保存在数组mFDs中：
- mFDs[mFDCount].fd = fd;
- mFDs[mFDCount].events = POLLIN;
- mFDs[mFDCount].revents = 0;
接下来查看这个设备是不是键盘：
- // Figure out the kinds of events the device reports.
- uint8_t key_bitmask[sizeof_bit_array(KEY_MAX + 1)];
- memset(key_bitmask, 0, sizeof(key_bitmask));
- LOGV("Getting keys...");
- if (ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(key_bitmask)), key_bitmask) >= 0) {
- // See if this is a keyboard. Ignore everything in the button range except for
- // gamepads which are also considered keyboards.
- if (containsNonZeroByte(key_bitmask, 0, sizeof_bit_array(BTN_MISC))
- || containsNonZeroByte(key_bitmask, sizeof_bit_array(BTN_GAMEPAD),
- sizeof_bit_array(BTN_DIGI))
- || containsNonZeroByte(key_bitmask, sizeof_bit_array(KEY_OK),
- sizeof_bit_array(KEY_MAX + 1))) {
- device->classes |= INPUT_DEVICE_CLASS_KEYBOARD;
- device->keyBitmask = new uint8_t[sizeof(key_bitmask)];
- if (device->keyBitmask != NULL) {
- memcpy(device->keyBitmask, key_bitmask, sizeof(key_bitmask));
- } else {
- delete device;
- LOGE("out of memory allocating key bitmask");
- return -1;
- }
- }
- }
如果是的话，还要继续进一步初始化前面为这个设备文件所创建的device_t结构体，主要就是把结构体device的classes成员变量的INPUT_DEVICE_CLASS_KEYBOARD位置为1了，以表明这是一个键盘。
如果是键盘设备，初始化工作还未完成，还要继续设置键盘的布局等信息：
- if ((device->classes & INPUT_DEVICE_CLASS_KEYBOARD) != 0) {
- char tmpfn[sizeof(name)];
- char keylayoutFilename[300];
- // a more descriptive name
- device->name = name;
- // replace all the spaces with underscores
- strcpy(tmpfn, name);
- for (char *p = strchr(tmpfn, ' '); p && *p; p = strchr(tmpfn, ' '))
- *p = '_';
- // find the .kl file we need for this device
- const char* root = getenv("ANDROID_ROOT");
- snprintf(keylayoutFilename, sizeof(keylayoutFilename),
- "%s/usr/keylayout/%s.kl", root, tmpfn);
- bool defaultKeymap = false;
- if (access(keylayoutFilename, R_OK)) {
- snprintf(keylayoutFilename, sizeof(keylayoutFilename),
- "%s/usr/keylayout/%s", root, "qwerty.kl");
- defaultKeymap = true;
- }
- status_t status = device->layoutMap->load(keylayoutFilename);
- if (status) {
- LOGE("Error %d loading key layout.", status);
- }
- // tell the world about the devname (the descriptive name)
- if (!mHaveFirstKeyboard && !defaultKeymap && strstr(name, "-keypad")) {
- // the built-in keyboard has a well-known device ID of 0,
- // this device better not go away.
- mHaveFirstKeyboard = true;
- mFirstKeyboardId = device->id;
- property_set("hw.keyboards.0.devname", name);
- } else {
- // ensure mFirstKeyboardId is set to -something-.
- if (mFirstKeyboardId == 0) {
- mFirstKeyboardId = device->id;
- }
- }
- char propName[100];
- sprintf(propName, "hw.keyboards.%u.devname", device->id);
- property_set(propName, name);
- // 'Q' key support = cheap test of whether this is an alpha-capable kbd
- if (hasKeycodeLocked(device, AKEYCODE_Q)) {
- device->classes |= INPUT_DEVICE_CLASS_ALPHAKEY;
- }
- // See if this device has a DPAD.
- if (hasKeycodeLocked(device, AKEYCODE_DPAD_UP) &&
- hasKeycodeLocked(device, AKEYCODE_DPAD_DOWN) &&
- hasKeycodeLocked(device, AKEYCODE_DPAD_LEFT) &&
- hasKeycodeLocked(device, AKEYCODE_DPAD_RIGHT) &&
- hasKeycodeLocked(device, AKEYCODE_DPAD_CENTER)) {
- device->classes |= INPUT_DEVICE_CLASS_DPAD;
- }
- // See if this device has a gamepad.
- for (size_t i = 0; i < sizeof(GAMEPAD_KEYCODES)/sizeof(GAMEPAD_KEYCODES[0]); i++) {
- if (hasKeycodeLocked(device, GAMEPAD_KEYCODES[i])) {
- device->classes |= INPUT_DEVICE_CLASS_GAMEPAD;
- break;
- }
- }
- LOGI("New keyboard: device->id=0x%x devname='%s' propName='%s' keylayout='%s'\n",
- device->id, name, propName, keylayoutFilename);
- }
到这里，系统中的输入设备文件就打开了。
本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/966619，如需转载请自行联系原作者
