* The declarations here have to be in a header file,
* because they need to be known both to the kernel
* module (in chardev.c) and the process calling ioctl (ioctl.c)
*/
#ifndef CHARDEV_H
#define CHARDEV_H #
include
/* The major device number. We can't rely on dynamic
* registration any more, because ioctls need to know it. */
#define MAJOR_NUM 100
/* Set the message of the device driver */
#define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *)
/* _IOR means that we're creating an ioctl command
* number for passing information from a user process
* to the kernel module.
*
* The first arguments, MAJOR_NUM, is the major device
* number we're using.
*
* The second argument is the number of the command
* (there could be several with different meanings).
*
* The third argument is the type we want to get from
* the process to the kernel. */
/* Get the message of the device driver */
#define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *)
/* This IOCTL is used for output, to get the message
* of the device driver. However, we still need the
* buffer to place the message in to be input,
* as it is allocated by the process. */
/* Get the n'th byte of the message */
#define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int)
/* The IOCTL is used for both input and output. It
* receives from the user a number, n, and returns Message[n]. */
/* The name of the device file */
#define DEVICE_FILE_NAME "char_dev"
#endif
/* 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. */
/* Copyright (C) 1998 by Ori Pomerantz */
/* device specifics, such as ioctl numbers and the major device file. */
#include "chardev.h"
#include
#include
#include
/* Functions for the ioctl calls */
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);
}
}
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);
}
