This program tests the ioctl.c example file systsem.
Compile with: 
gcc -Wall ioctl_client.c -o ioctl_client
 
Source code
 
 
 
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <errno.h>
#include <unistd.h>
 
const char *usage =
"Usage: fioclient FIOC_FILE [size]\n"
"\n"
"Get size if <size> is omitted, set size otherwise\n"
"\n";
 
int main(int argc, char **argv)
{
        size_t size;
        int fd;
        int ret = 0;
 
        if (argc < 2) {
                fprintf(stderr, "%s", usage);
                return 1;
        }
 
        fd = open(argv[1], O_RDWR);
        if (fd < 0) {
                perror("open");
                return 1;
        }
 
        if (argc == 2) {
                if (ioctl(fd, FIOC_GET_SIZE, &size)) {
                        perror("ioctl");
                        ret = 1;
                        goto out;
                }
                printf("%zu\n", size);
        } else {
                size = strtoul(argv[2], NULL, 0);
                if (ioctl(fd, FIOC_SET_SIZE, &size)) {
                        perror("ioctl");
                        ret = 1;
                        goto out;
                }
        }
out:
        close(fd);
        return ret;
}
  
Definition in file ioctl_client.c.