Uinput Module

kernel/Documentation/input/uinput.rst

Introduction

uinput是一个内核模块，可以从用户空间模拟输入设备。通过写入/dev/uinput（或 /dev/input/uinport）设备，进程可以创建具有特定功能的虚拟输入设备。一旦创建了这个虚拟设备，进程就可以通过它发送事件，这些事件将传递给用户空间和内核中事件消费者。

Interface

linux/uinput.h

uinpu t头定义 ioctl 来创建、设置和销毁虚拟设备。

libevdev

libevdev 是 evdev设备的包装库，它提供了创建 uinput设备和发送事件的接口。libevdev比直接访问uinput 更不容易出错，新软件应该考虑使用此方式。

有关 libevdev 的示例和更多信息： https://www.freedesktop.org/s...

Examples

Keyboard events

第一个示例演示了如何创建新的虚拟设备，以及如何发送关键事件。为了简单起见，删除了所有默认导入和错误处理程序。

   #include <linux/uinput.h>

   void emit(int fd, int type, int code, int val)
   {
      struct input_event ie;

      ie.type = type;
      ie.code = code;
      ie.value = val;
      /* timestamp values below are ignored */
      ie.time.tv_sec = 0;
      ie.time.tv_usec = 0;

      write(fd, &ie, sizeof(ie));
   }

   int main(void)
   {
      struct uinput_setup usetup;

      int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);


      /*
       * The ioctls below will enable the device that is about to be
       * created, to pass key events, in this case the space key.
       */
      ioctl(fd, UI_SET_EVBIT, EV_KEY);
      ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);

      memset(&usetup, 0, sizeof(usetup));
      usetup.id.bustype = BUS_USB;
      usetup.id.vendor = 0x1234; /* sample vendor */
      usetup.id.product = 0x5678; /* sample product */
      strcpy(usetup.name, "Example device");

      ioctl(fd, UI_DEV_SETUP, &usetup);
      ioctl(fd, UI_DEV_CREATE);

      /*
       * On UI_DEV_CREATE the kernel will create the device node for this
       * device. We are inserting a pause here so that userspace has time
       * to detect, initialize the new device, and can start listening to
       * the event, otherwise it will not notice the event we are about
       * to send. This pause is only needed in our example code!
       */
      sleep(1);

      /* Key press, report the event, send key release, and report again */
      emit(fd, EV_KEY, KEY_SPACE, 1);
      emit(fd, EV_SYN, SYN_REPORT, 0);
      emit(fd, EV_KEY, KEY_SPACE, 0);
      emit(fd, EV_SYN, SYN_REPORT, 0);

      /*
       * Give userspace some time to read the events before we destroy the
       * device with UI_DEV_DESTROY.
       */
      sleep(1);

      ioctl(fd, UI_DEV_DESTROY);
      close(fd);

      return 0;
   }       

Mouse movements

这个例子展示了如何创建一个行为类似于物理鼠标的虚拟设备。

   #include <linux/uinput.h>

   /* emit function is identical to of the first example */

   int main(void)
   {
      struct uinput_setup usetup;
      int i = 50;

      int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);

      /* enable mouse button left and relative events */
      ioctl(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);

      memset(&usetup, 0, sizeof(usetup));
      usetup.id.bustype = BUS_USB;
      usetup.id.vendor = 0x1234; /* sample vendor */
      usetup.id.product = 0x5678; /* sample product */
      strcpy(usetup.name, "Example device");

      ioctl(fd, UI_DEV_SETUP, &usetup);
      ioctl(fd, UI_DEV_CREATE);

      /*
       * On UI_DEV_CREATE the kernel will create the device node for this
       * device. We are inserting a pause here so that userspace has time
       * to detect, initialize the new device, and can start listening to
       * the event, otherwise it will not notice the event we are about
       * to send. This pause is only needed in our example code!
       */
      sleep(1);

      /* Move the mouse diagonally, 5 units per axis */
      while (i--) {
         emit(fd, EV_REL, REL_X, 5);
         emit(fd, EV_REL, REL_Y, 5);
         emit(fd, EV_SYN, SYN_REPORT, 0);
         usleep(15000);
      }

      /*
       * Give userspace some time to read the events before we destroy the
       * device with UI_DEV_DESTROY.
       */
      sleep(1);

      ioctl(fd, UI_DEV_DESTROY);
      close(fd);

      return 0;
   }   

uinput old interface

在 uinput 版本5之前，没有专门的 ioctl 来设置虚拟设备。较旧版本的 uinput接口需要填充 uinput_user_dev 结构，并将其写入uinput文件描述符以配置新的 uinport设备。新代码不应该使用旧接口，而是通过 ioctl 调用与uinput交互，或者使用 libevdev。

   #include <linux/uinput.h>

   /* emit function is identical to of the first example */

   int main(void)
   {
      struct uinput_user_dev uud;
      int version, rc, fd;

      fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
      rc = ioctl(fd, UI_GET_VERSION, &version);

      if (rc == 0 && version >= 5) {
         /* use UI_DEV_SETUP */
         return 0;
      }

      /*
       * The ioctls below will enable the device that is about to be
       * created, to pass key events, in this case the space key.
       */
      ioctl(fd, UI_SET_EVBIT, EV_KEY);
      ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);

      memset(&uud, 0, sizeof(uud));
      snprintf(uud.name, UINPUT_MAX_NAME_SIZE, "uinput old interface");
      write(fd, &uud, sizeof(uud));
       
      ioctl(fd, UI_DEV_CREATE);

      /*
       * On UI_DEV_CREATE the kernel will create the device node for this
       * device. We are inserting a pause here so that userspace has time
       * to detect, initialize the new device, and can start listening to
       * the event, otherwise it will not notice the event we are about
       * to send. This pause is only needed in our example code!
       */
      sleep(1);

      /* Key press, report the event, send key release, and report again */
      emit(fd, EV_KEY, KEY_SPACE, 1);
      emit(fd, EV_SYN, SYN_REPORT, 0);
      emit(fd, EV_KEY, KEY_SPACE, 0);
      emit(fd, EV_SYN, SYN_REPORT, 0);

      /*
       * Give userspace some time to read the events before we destroy the
       * device with UI_DEV_DESTROY.
       */
      sleep(1);

      ioctl(fd, UI_DEV_DESTROY);

      close(fd);
      return 0;
   }