char driver demo

chardev.c

#include "chardev.h"
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/uaccess.h>

//global varibles
static int unused=1;
static int number=0;
static char msg[N]="13111387\0";
static char *cur;
static int cdv_open(struct inode *inode,struct file *filp)
{
    printk(KERN_INFO "unused:%d\n",unused);
    if (!unused)
        return -EBUSY;
    unused=0;
    cur=msg;
    try_module_get(THIS_MODULE);
    return 0;
}
static int cdv_release(struct inode *inode,struct file *file)
{
    unused=1;
    cur=msg;
    module_put(THIS_MODULE);
    return 0;
}
static ssize_t cdv_read(struct file *filp,char *buffer,size_t length,loff_t *offset)
{
    int notread=strlen(cur);
    if (!notread)
        return 0;
    if (length>notread)
        length=notread;
    copy_to_user(buffer,cur,length);
    cur+=length;
    return length;
}
static ssize_t cdv_write(struct file *filp,const char *buffer,size_t length,loff_t *offset)
{
    int canwrite=strlen(cur);
    if (length>N-(cur-msg))
        length=N-(cur-msg);
    copy_from_user(cur,buffer,length);
    cur+=length;
    return length;
}
static int cdv_ioctl(struct file *filp,unsigned int cmd,unsigned long arg)
{
    printk(KERN_INFO "ioctl CLEAR.\n");
    printk(KERN_INFO "cmd:%d\nCLEAR:%d\n",cmd,CDV_CLEAR);
    if (cmd==CDV_CLEAR)
    {
        printk(KERN_INFO "ioctl CLEAR.\n");
        *msg='\0';
    }
    return 0;
}

//file_operations
struct file_operations fops={
    .open=cdv_open,
    .release=cdv_release,
    .read=cdv_read,
    .write=cdv_write,
    .unlocked_ioctl=cdv_ioctl,
    .compat_ioctl=cdv_ioctl
};
int init_cdv(void)
{
    number=register_chrdev(number,NAME,&fops);
    if(number<0)
    {
        printk(KERN_INFO "Registering char device failed with %d\n",number);
        return number;
    }
    printk(KERN_INFO "ok\n");
    printk(KERN_INFO "I was assigned major number %d. To talk to\n", number);
	printk(KERN_INFO "the driver, create a dev file with\n");
	printk(KERN_INFO "'mknod /dev/%s c %d 0'.\n", NAME, number);
	printk(KERN_INFO "Try various minor numbers. Try to cat and echo to\n");
	printk(KERN_INFO "the device file.\n");
	printk(KERN_INFO "Remove the device file and module when done.\n");
    return 0;
}
void cleanup_cdv(void)
{
    unregister_chrdev(number,NAME);
    printk(KERN_INFO "bye\n");
}
module_init(init_cdv);
module_exit(cleanup_cdv);

chardev.h

#ifndef H_CHARDEV
#define H_CHARDEV

#define NAME "chardev"
#define CDV_CLEAR 0x909090
#define N 1024
#endif

cleaner.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <fcntl.h>

#include "chardev.h"

int main(int argc,char *argv[])
{
    int fd,ret;
    fd=open("/dev/chardev",O_RDWR);
    if(fd<0)
    {
        printf("open error.\n");
        exit(1);
    }
    ret=ioctl(fd,CDV_CLEAR,0);
    if (ret<0)
    {
        printf("ioctl error.\n");
        exit(1);
    }
    close(fd);
    printf("ioctl success.\n");
    return 0;
}