klist_example.c

#include <stdio.h>
#include <fcntl.h>
#include <stropts.h>
#include <unistd.h>
#include <stdlib.h>
#include <limits.h>
#include <signal.h>
#include <errno.h>

#define LIST_CMD 0x1337
#define LIST_ADD (LIST_CMD + 0)
#define LIST_INSERT (LIST_CMD + 1)
#define LIST_SET (LIST_CMD + 2)
#define LIST_GET (LIST_CMD + 3)
#define LIST_DELETE (LIST_CMD + 4)

struct index_val_t {
    unsigned long index;
    long value;
};

int main() {
    int fd = open("/dev/klist", O_RDWR);
    struct index_val_t tmp;
    
    tmp.index = 0;
    tmp.value = 0x1337;
    if (!ioctl(fd, LIST_INSERT, &tmp)) {
        printf("Write successfull\n");
    }
    
    tmp.index = 0;
    tmp.value = 0;
    if (!ioctl(fd, LIST_GET, &tmp)) {
        printf("%04x\n", tmp.value);
    }
    
    close(fd);
    return EXIT_SUCCESS;
}