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#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include "chardev.h"
#define SUCCESS 0
#define DEVICE_NAME "chardev"
#define BUF_LEN 80
static int Major;
static int opened = 0;
static char msg[BUF_LEN];
static char* msg_ptr;
static struct file_operations fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release = device_release
};
int init_module(void)
{
Major = register_chrdev(0, DEVICE_NAME, &fops);
if (Major < 0) {
printk(KERN_ALERT "Registering char device failed with %d\n", Major);
return Major;
}
printk(KERN_INFO "I was assigned major number %d. To talk to\n", Major);
printk(KERN_INFO "the driver, create a dev file with\n");
printk(KERN_INFO "'mknod /dev/%s c %d 0'.\n", DEVICE_NAME, Major);
printk(KERN_INFO "Try to cat and echo to the device file.\n");
printk(KERN_INFO "Remove the device file and module when done.\n");
return SUCCESS;
}
void cleanup_module(void)
{
unregister_chrdev(Major, DEVICE_NAME);
}
static int device_open(struct inode* inode, struct file* filp)
{
static int counter = 0;
if (opened)
return -EBUSY;
opened++;
if (counter++ == 0)
sprintf(msg, "Come on, write something here :D\n");
msg_ptr = msg;
try_module_get(THIS_MODULE);
return SUCCESS;
}
static int device_release(struct inode* inode, struct file* filp)
{
opened--;
module_put(THIS_MODULE);
return 0;
}
static ssize_t device_read(struct file* filp, char* buffer, size_t len, loff_t* off)
{
int bytes = 0;
if (*msg_ptr == 0)
return 0;
while (len-- && *msg_ptr) {
put_user(*msg_ptr++, buffer++);
bytes++;
}
return bytes;
}
static ssize_t device_write(struct file* filp, const char* buff, size_t len, loff_t* off)
{
int bytes = 0;
if (len > BUF_LEN) {
printk(KERN_ALERT "Error: dude you tried to overflow my buffer!\n");
return -ENOBUFS;
}
while (len--) {
get_user(msg[bytes], buff++);
bytes++;
}
msg[bytes] = '\0';
msg_ptr = msg;
return bytes;
}
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