Linux操作系统内核和设备文件对话(1)(6)

* The first arguments, MAJOR_NUM, is the major device

* number were 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 nth 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

ex ioctl.c

/* ioctl.c - the process to use ioctls to control the

* kernel module

*

* Until now we could have used cat for input and

* output. But now we need to do ioctls, 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 /* open */

#include /* exit */

#include /* ioctl */

/* 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 dont tell

* the kernel how far its 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);

}

ioctl_get_nth_byte(int file_desc)

{

int i;

char c;

printf("get_nth_byte message:");

i = 0;

while (c != 0) {

c = ioctl(file_desc, IOCTL_GET_NTH_BYTE, i++);

if (c < 0) {

printf(

"ioctl_get_nth_byte failed at the %dth byte:\n", i);

exit(-1);

}

putchar(c);

}

putchar(\n);

}

/* Main - Call the ioctl functions */

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 ("Cant 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);

}