LKMPG/4.7.4/examples/other/ioctl.c

/*
 *  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>
#include <stdlib.h>
#include <fcntl.h>              /* open */
#include <unistd.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);
        exit(-1);
    }
    return 0;
}

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

    /*
     * 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);
        exit(-1);
    }

    printf("get_msg message:%s\n", message);
    return 0;
}

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

    printf("get_nth_byte message:");

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

        if (c < 0) {
            printf("ioctl_get_nth_byte failed at the %d'th byte:\n",
                   i);
            exit(-1);
        }

        putchar(c);
    } while (c != 0);
    putchar('\n');
    return 0;
}

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

    file_desc = open(DEVICE_FILE_NAME, 0);
    if (file_desc < 0) {
        printf("Can't open device file: %s\n", DEVICE_FILE_NAME);
        exit(-1);
    }

    ioctl_get_nth_byte(file_desc);
    ioctl_get_msg(file_desc);
    ioctl_set_msg(file_desc, msg);

    close(file_desc);
    return 0;
}