Filters keycodes from R400 presenter in Linux

ioctlfilter.c

/* Grabs all input from Logitech R400 presenter and filters to ensure only certain keys are pressed.
 * Ensures that only valid R400 keys are pressed and not rogue keys injected.
 * Main logic for this found here: http://stackoverflow.com/questions/7668872/need-to-intercept-hid-keyboard-events-and-then-block-them
 * Author: Etienne Stalmans <[email protected]>
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <dirent.h>
#include <linux/input.h>
#include <linux/uinput.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <termios.h>
#include <signal.h>

int main(int argc, char* argv[])
{
    struct input_event ev[64];
    int fevdev = -1;
    int inputdev = -1;
    int result = 0;
    int size = sizeof(struct input_event);
    int rd;
    int value;
    char name[256] = "Logitech USB Receiver";
    char *device = "/dev/input/by-id/usb-Logitech_USB_Receiver-event-kbd";
    
    //get handle to keyboard, so we can forward keys
    inputdev =  open("/dev/input/event3",O_WRONLY|O_NONBLOCK);
    if (inputdev == -1) {
        printf("Failed to open keyboard device.\n");
        exit(1);
    }
    
    //open handle to our logitech receiver
    fevdev = open(device, O_RDONLY);
    if (fevdev == -1) {
        printf("Failed to open event device.\n");
        exit(1);
    }

    result = ioctl(fevdev, EVIOCGNAME(sizeof(name)), name);
    printf ("Reading From : %s (%s)\n", device, name);

    printf("Getting exclusive access: ");
    result = ioctl(fevdev, EVIOCGRAB, 1);
    printf("%s\n", (result == 0) ? "SUCCESS" : "FAILURE");

    while (1)
    {
        if ((rd = read(fevdev, ev, size * 64)) < size) {
            break;
        }

        value = ev[0].value;
        //check whether key_press or key_release
        if (value != ' ' && (ev[1].value == 1 || ev[1].value == 0) && ev[1].type == 1 ) {
            //printf ("Code[%d] Type[%d]\n", (ev[1].code),(ev[1].type));
            //check that it is a valid key
            if (ev[1].code == 109 ||ev[1].code == 104||ev[1].code == 52 || ev[1].code== 63){
                write(inputdev,&ev,sizeof(ev));
            }
        }
    }

    
    printf("Exiting.\n");
    result = ioctl(fevdev, EVIOCGRAB, 0);
    close(fevdev);
    close(inputdev);
    return 0;
}

Replace https://gist.github.com/staaldraad/ec3007ccb9289d407c70e63162d03c69#file-ioctlfilter-c-L33 with your device location.
Replace https://gist.github.com/staaldraad/ec3007ccb9289d407c70e63162d03c69#file-ioctlfilter-c-L36 with your input event for your keyboard.

compile with gcc
gcc ioctlfilter.c -o ioctlfilter
run with root/sudo

sudo ./ioctlfilter