7. uinput 模組

7.1. 介紹

uinput 是一個核心模組，它使得從使用者空間模擬輸入裝置成為可能。透過寫入 /dev/uinput (或 /dev/input/uinput) 裝置，一個程序可以建立一個具有特定功能的虛擬輸入裝置。 一旦建立了這個虛擬裝置，程序就可以透過它傳送事件，這些事件將被傳遞給使用者空間和核心消費者。

7.2. 介面

linux/uinput.h

uinput 標頭檔案定義了用於建立、設定和銷燬虛擬裝置的 ioctl。

7.3. libevdev

libevdev 是 evdev 裝置的包裝庫，它提供了建立 uinput 裝置和傳送事件的介面。 libevdev 比直接訪問 uinput 更不容易出錯，對於新的軟體應該考慮使用它。

有關 libevdev 的示例和更多資訊：https://www.freedesktop.org/software/libevdev/doc/latest/

7.4. 示例

7.4.1. 鍵盤事件

第一個例子展示瞭如何建立一個新的虛擬裝置，以及如何傳送一個按鍵事件。為了簡單起見，所有預設匯入和錯誤處理程式都被移除。

#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;
}

7.4.2. 滑鼠移動

這個例子展示瞭如何建立一個行為類似於物理滑鼠的虛擬裝置。

#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;
}

7.4.3. uinput 舊介面

在 uinput 版本 5 之前，沒有專門的 ioctl 來設定虛擬裝置。 支援舊版本 uinput 介面的程式需要填充一個 uinput_user_dev 結構，並將其寫入 uinput 檔案描述符來配置新的 uinput 裝置。 新的程式碼不應該使用舊介面，而是透過 ioctl 呼叫與 uinput 互動，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;
}