Linux Kernel（20.2）- uinput module

uinput是kernel module透過寫入/dev/uinput從userpace模擬input device裝置，並且驅動特定的event。
其kernel configuration的path為Input device support -> Miscellaneous devices -> User level driver support
設定簡單，可以參考以下範例大概就知道如何操控了。

#include <stdio.h>
#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <unistd.h>

#include <string.h>

#include <linux/input.h>

#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!
   **/
  printf("will report the event after 10 sec\n");
  sleep(10);

  /* 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_DESTOY.
   **/
  sleep(1);

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

  return 0;
}

執行結果，input_test為先前章節的user space程式，uinput為該章節範例，執行uinput之後，會在/dev/input/長出對應的device node。

/ # zcat /proc/config.gz | grep UINPUT
CONFIG_INPUT_UINPUT=y
/ # ./uinput &
/ # [   99.433163] input: Example device as /devices/virtual/input/input4
/ # ls /dev/input/
event0  event1
/ # ./input_test /dev/input/event1
will report the event after 10 sec
type:1, code:57, val:1
type:0, code:0, val:0
type:1, code:57, val:0
type:0, code:0, val:0

參考資料:
• Documentation/input/uinput.rst