Thread: uinput module keyboard events

hi, i'm trying to emulate keypress with uinput kernel module.
i've found this code snippet in documentation 7. uinput module — The Linux Kernel documentation

Code:

#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;
}

after adding the headers missing, this snippet compiles ok, but I can't see the result of its work.

the expected result is that the program should send a key press of "SPACE" system-wide, so i'm trying to catch it with putting the cursor in gedit after I start the program, but nothing happens

please tell me what i'm doing wrong

sorry, these are my first steps in C and linux programming)
i'm just trying to run the example in kernel manual

Code:

    int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
    if (fd == -1) {
        fprintf(stderr, "Cannot open device: %s.\n", strerror(errno));
        return EXIT_FAILURE;
    }

Code:

int r = ioctl(fd, UI_SET_EVBIT, EV_KEY);
if (r != 0) {
        fprintf(stderr, "Cannot enable device: %s.\n", strerror(errno));
        return EXIT_FAILURE;
    }

is this a correct way to handle errors?

yes, the problem was I've launched the program with user privileges, so it couldn't open the device
with sudo this snippet works

thank you!