在Linux下实现一个使用键盘控制的虚拟鼠标

在Linux下创建一个虚拟鼠标设备还是比较简单的，使用内核uinput模块提供的函数即可。创建出虚拟鼠标以后，在主线程监听键盘的事件，当特定的键（此处使用了小键盘的数字键8、2、4、6）被按下或弹起后，进行记录。在另一个线程根据主线程记录的flag创建输入事件，然后将输入事件写入虚拟鼠标设备即可。
在实现程序时一个让我思考时间比较长的问题是：是否需要另外创建一个线程来写虚拟鼠标设备。当一个键被按下后，我们需要不断的写向相应方向移动的事件，这里是需要定时循环写的。如果不另开线程的话，我们需要在这个循环中先使用select或poll读键盘事件，可能等到了事件，也可能等不到事件；然后对相应的键进行记录；然后写虚拟鼠标设备；最后睡眠一定的时间，睡眠的时间是受前面等待事件的时间影响的，这样才能使得每个循环花费时间是相同的。这样做应该也行得通，但我觉得不如另开一个线程，在两个循环里分别读写事件实现起来比较方便。不过另开线程需要为线程安全做一点小工作，原因是有些flag可能需要在两个线程里写，使用标准库提供的atomic模板就能做到。
原本以为没几行代码，没想到写着写着就长了，功能也不太全，没有实现左右按键的功能，不过好歹能直接跑起来，有需要的时候进行扩展就是了。实现代码时主要参考了这些资料：
https://www.kernel.org/doc/html/v4.12/input/uinput.html
https://cgit.freedesktop.org/evtest
代码地址为：https://github.com/im-red/virtualmouse
也把代码贴在这里：

#include <err.h>
#include <stdio.h>
#include <assert.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/uinput.h>
#include <string.h>
#include <dirent.h>
#include <vector>
#include <string>
#include <iostream>
#include <poll.h>
#include <signal.h>
#include <pthread.h>
#include <atomic>#define STR(X) STR2(X)
#define STR2(X) #X#define ENSURE(CONDITION, ...) if (!(CONDITION)) { err(EXIT_FAILURE, __FILE__ ":" STR(__LINE__) " " __VA_ARGS__); }static const char *EVENT_DEV_NAME = "event";
static const char *EVENT_DEV_PREFIX = "/dev/input/";
static const char *UINPUT_NAME = "/dev/uinput";static const int BITS_PER_LONG = sizeof(long) * 8;inline int nbytes(int x)
{return (x - 1) / BITS_PER_LONG + 1;
}inline bool testBits(int bit, const unsigned long array[])
{unsigned long result = array[bit / BITS_PER_LONG] >> bit % BITS_PER_LONG & 1;return (result == 1);
}static int isEventDevice(const struct dirent *dir)
{return strncmp(EVENT_DEV_NAME, dir->d_name, strlen(EVENT_DEV_NAME)) == 0;
}static void createVirtualMouse(int fd)
{// enable mouse button left and relative eventsioctl(fd, UI_SET_EVBIT, EV_KEY);ioctl(fd, UI_SET_KEYBIT, BTN_LEFT);ioctl(fd, UI_SET_EVBIT, EV_REL);ioctl(fd, UI_SET_RELBIT, REL_X);ioctl(fd, UI_SET_RELBIT, REL_Y);struct uinput_user_dev uud;memset(&uud, 0, sizeof(uud));snprintf(uud.name, UINPUT_MAX_NAME_SIZE, "Virtual Mouse");int ret = write(fd, &uud, sizeof(uud));ENSURE(ret == sizeof(uud));ioctl(fd, UI_DEV_CREATE);
}static std::vector<std::string> getAllEventDevicePath()
{struct dirent **direntList;int ndev = scandir(EVENT_DEV_PREFIX, &direntList, isEventDevice, versionsort);ENSURE(ndev > 0, "No event device found");std::vector<std::string> result(ndev);for (int i = 0; i < ndev; i++){result[i] = std::string(EVENT_DEV_PREFIX) + std::string(direntList[i]->d_name);}return std::move(result);
}// A simple RAII class
class FileOpener
{public:explicit FileOpener(const char *pathname, int flags){fd = open(pathname, flags);}explicit FileOpener(const char *pathname, int flags, mode_t mode){fd = open(pathname, flags, mode);}~FileOpener(){if (fd >= 0){close(fd);}}int getFd(){return fd;}private:int fd;
};static bool isSupportType(const std::string &path, int type)
{FileOpener opener(path.c_str(), O_RDONLY);int fd = opener.getFd();if (fd < 0){return false;}unsigned long supportType[nbytes(EV_MAX)];ioctl(fd, EVIOCGBIT(0, EV_MAX), supportType);if (!testBits(type, supportType)){return false;}return true;
}static bool isSupportTypeCode(const std::string &path, int type, int code)
{if (!isSupportType(path, type)){return false;}FileOpener opener(path.c_str(), O_RDONLY);int fd = opener.getFd();if (fd < 0){return false;}unsigned long supportCode[nbytes(KEY_MAX)];ioctl(fd, EVIOCGBIT(type, KEY_MAX), supportCode);if (!testBits(code, supportCode)){return false;}return true;
}static const int NEEDED_KEY[] = { KEY_KP8, KEY_KP2, KEY_KP4, KEY_KP6 };
// device reports KEY_KP8 KEY_KP2 KEY_KP4 KEY_KP6 is valid keyboard
static bool isValidKeyboard(const std::string &path)
{for (unsigned int i = 0; i < (sizeof(NEEDED_KEY) / sizeof(int)); i++){if (!isSupportTypeCode(path, EV_KEY, NEEDED_KEY[i])){return false;}}return true;
}static std::vector<std::string> getAllValidKeyboard()
{std::vector<std::string> validDevice;std::vector<std::string> allDevice = getAllEventDevicePath();for (unsigned int i = 0; i < allDevice.size(); i++){if (isValidKeyboard(allDevice[i])){validDevice.push_back(allDevice[i]);}}return validDevice;
}static std::string getOneNumLockDevice()
{std::vector<std::string> allDevice = getAllEventDevicePath();for (unsigned int i = 0; i < allDevice.size(); i++){if (isSupportTypeCode(allDevice[i], EV_LED, LED_CAPSL)){return allDevice[i];}}return std::string("");
}static int uinputFd = 0;// program should exit
static volatile bool shouldStop = false;// if numlock is on, we don't move mouse
static bool numlockOn = false;const static int UP = 0;
const static int DOWN = 1;
const static int LEFT = 2;
const static int RIGHT = 3;
const static int DIRECTION_NUM = 4;// move status
// change to true/false when corresponding key is pressed/released
static bool isMoving[DIRECTION_NUM] = { false };// move times from the point that corresponding key is pressed
// reset to 0 when key is released
static std::atomic_int moveTimes[DIRECTION_NUM];inline void resetMoveTimes()
{for (int i = 0; i < DIRECTION_NUM; i++){moveTimes[i] = 0;}
}// move step is affected by move times
// so we can apply some acceleration strategy
static int moveStep(int times)
{const int MIN_STEP = 1;const int MAX_STEP = 10;const int MIN_POINT = 50;const int MAX_POINT = 200;if (times <= MIN_POINT){return MIN_STEP;}else if (times <= MAX_POINT){return MIN_STEP + (times - MIN_POINT) * 1.0 / (MAX_POINT - MIN_POINT) * (MAX_STEP - MIN_STEP);}else{return MAX_STEP;}
}// write mouse move event every timeInterval ms
static int timeInterval = 10;static void setIsMoving(int index, int value)
{isMoving[index] = value;if (!value){moveTimes[index] = 0;}
}static void keyAction(int index, int value)
{ENSURE(index >= 0 && index < DIRECTION_NUM);if (value == 1){setIsMoving(index, true);}else if (value == 0){setIsMoving(index, false);}else{// do nothing}
}static void handleKeyEvent(const struct input_event &ev)
{if (numlockOn){return;}int index = -1;switch (ev.code){case KEY_KP8: index = UP; break;case KEY_KP2: index = DOWN; break;case KEY_KP4: index = LEFT; break;case KEY_KP6: index = RIGHT; break;default: index = -1; break;}if (index != -1){keyAction(index, ev.value);}
}static void handleLEDEvent(const struct input_event &ev)
{if (ev.code == LED_NUML){if (ev.value == 0){numlockOn = false;}else if (ev.value == 1){numlockOn = true;for (int i = 0; i < DIRECTION_NUM; i++){setIsMoving(i, false);}}}
}static void handleEvent(const struct input_event &ev)
{if (ev.type == EV_KEY){handleKeyEvent(ev);}else if (ev.type == EV_LED){handleLEDEvent(ev);}
}static void handleDevice(int fd)
{struct input_event ev[64];int rd = read(fd, ev, sizeof(ev));ENSURE(rd % sizeof(struct input_event) == 0, "expected %d bytes, got %d\n", (int) sizeof(struct input_event), rd % (int) sizeof(struct input_event));int n = rd / sizeof(struct input_event);for (int j = 0; j < n; j++){handleEvent(ev[j]);}
}static void interrupt_handler(int sig)
{(void) sig;shouldStop = true;
}static bool queryNumlock()
{std::string ledDevice = getOneNumLockDevice();// if there is no led device, we suppose that numlock is always offif (ledDevice == std::string("")){return false;}FileOpener opener(ledDevice.c_str(), O_RDONLY);int fd = opener.getFd();ENSURE(fd >= 0);unsigned long supportLED[nbytes(LED_MAX)];ioctl(fd, EVIOCGLED(sizeof(supportLED)), supportLED);if (testBits(LED_NUML, supportLED)){return true;}else{return false;}
}static void incMoveTimes()
{for (int i = 0; i < DIRECTION_NUM; i++){if (isMoving[i]){moveTimes[i]++;}}
}static void calcMoveSteps(int *steps)
{for (int i = 0; i < DIRECTION_NUM; i++){if (isMoving[i]){steps[i] = moveStep(moveTimes[i]);}}// if opposite key is pressed, we set the steps all to 0if (isMoving[UP] && isMoving[DOWN]){steps[UP] = 0;steps[DOWN] = 0;}if (isMoving[LEFT] && isMoving[RIGHT]){steps[LEFT] = 0;steps[RIGHT] = 0;}
}// ok, let's write device to move the mouse
static void writeDevice(int *steps)
{int x = steps[RIGHT] - steps[LEFT];int y = steps[DOWN] - steps[UP];struct input_event ev[3];memset(ev, 0, sizeof(ev));ev[0].type = EV_REL;ev[0].code = REL_X;ev[0].value = x;ev[1].type = EV_REL;ev[1].code = REL_Y;ev[1].value = y;ev[2].type = EV_SYN;ev[2].code = SYN_REPORT;int ret = write(uinputFd, ev, sizeof(ev));ENSURE(ret == sizeof(ev));
}static void moveMouse()
{incMoveTimes();int steps[DIRECTION_NUM] = { 0 };calcMoveSteps(steps);writeDevice(steps);
}static void *moveMouseThread(void *arg)
{(void) arg;while(true){moveMouse();usleep(timeInterval * 1000);}return nullptr;
}int main()
{uinputFd  = open(UINPUT_NAME, O_WRONLY);ENSURE(uinputFd >= 0);createVirtualMouse(uinputFd);numlockOn = queryNumlock();std::vector<std::string> kbds = getAllValidKeyboard();ENSURE(kbds.size() >= 1, "There should be at least one keyboard");struct pollfd fds[kbds.size()];memset(fds, 0, sizeof(fds));for (unsigned int i = 0; i < kbds.size(); i++){fds[i].fd = open(kbds[i].c_str(), O_RDONLY);ENSURE(fds[i].fd >= 0, "Open keyboard %s failed", kbds[i].c_str());fds[i].events = POLLIN;}signal(SIGINT, interrupt_handler);signal(SIGTERM, interrupt_handler);pthread_t tid;int ret = pthread_create(&tid, nullptr, moveMouseThread, nullptr);ENSURE(ret == 0);resetMoveTimes();while (!shouldStop){for (unsigned int i = 0; i < kbds.size(); i++){fds[i].revents = 0;}poll(fds, kbds.size(), -1);for (unsigned int i = 0; i < kbds.size(); i++){if (fds[i].revents & POLLIN){handleDevice(fds[i].fd);}}}for (unsigned int i = 0; i < kbds.size(); i++){close(fds[i].fd);}return 0;
}

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