lkmpg/examples/other/userspace_ioctl.c

/*  userspace_ioctl.c - the process to use ioctl's to control the kernel module
 *
 *  Until now we could have used cat for input and output.  But now
 *  we need to do ioctl's, which require writing our own process. 
 */

/* device specifics, such as ioctl numbers and the 
 * major device file. */
#include "../chardev.h"

#include <stdio.h> /* standard I/O */
#include <fcntl.h> /* open */
#include <unistd.h> /* close */
#include <stdlib.h> /* exit */
#include <sys/ioctl.h> /* ioctl */

/* Functions for the ioctl calls */

int ioctl_set_msg(int file_desc, char *message)
{
    int ret_val;

    ret_val = ioctl(file_desc, IOCTL_SET_MSG, message);

    if (ret_val < 0) {
        printf("ioctl_set_msg failed:%d\n", ret_val);
    }

    return ret_val;
}

int ioctl_get_msg(int file_desc)
{
    int ret_val;
    char message[100] = { 0 };

    /* Warning - this is dangerous because we don't tell 
   * the kernel how far it's allowed to write, so it 
   * might overflow the buffer. In a real production 
   * program, we would have used two ioctls - one to tell
   * the kernel the buffer length and another to give 
   * it the buffer to fill
   */
    ret_val = ioctl(file_desc, IOCTL_GET_MSG, message);

    if (ret_val < 0) {
        printf("ioctl_get_msg failed:%d\n", ret_val);
    }
    printf("get_msg message:%s", message);

    return ret_val;
}

int ioctl_get_nth_byte(int file_desc)
{
    int i, c;

    printf("get_nth_byte message:");

    i = 0;
    do {
        c = ioctl(file_desc, IOCTL_GET_NTH_BYTE, i++);

        if (c < 0) {
            printf("\nioctl_get_nth_byte failed at the %d'th byte:\n", i);
            return c;
        }

        putchar(c);
    } while (c != 0);

    return 0;
}

/* Main - Call the ioctl functions */
int main(void)
{
    int file_desc, ret_val;
    char *msg = "Message passed by ioctl\n";

    file_desc = open(DEVICE_PATH, O_RDWR);
    if (file_desc < 0) {
        printf("Can't open device file: %s, error:%d\n", DEVICE_PATH,
               file_desc);
        exit(EXIT_FAILURE);
    }

    ret_val = ioctl_set_msg(file_desc, msg);
    if (ret_val)
        goto error;
    ret_val = ioctl_get_nth_byte(file_desc);
    if (ret_val)
        goto error;
    ret_val = ioctl_get_msg(file_desc);
    if (ret_val)
        goto error;

    close(file_desc);
    return 0;
error:
    close(file_desc);
    exit(EXIT_FAILURE);
}