#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h> /* everything... */
#include <linux/cdev.h>
#include <asm/uaccess.h> /* copy_*_user */
int scull_major = 0;
int scull_minor = 0;
struct cdev cdev; /* Char device structure */
#define MAX_SIZE 10
size_t size = 0;
char store[MAX_SIZE];
/*
* Open and close
*/
int scull_open(struct inode *inode, struct file *filp)
{
/* trim to 0 the length of the device if open was write-only */
if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
size = 0;
}
return 0; /* success */
}
int scull_release(struct inode *inode, struct file *filp)
{
return 0;
}
/*
* Data management: read and write
*/
ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
loff_t *f_pos)
{
ssize_t retval = 0;
if (*f_pos >= size)
goto out;
if (*f_pos + count > size)
count = size - *f_pos;
if (copy_to_user(buf, store + *f_pos, count)) {
retval = -EFAULT;
goto out;
}
*f_pos += count;
retval = count;
out:
return retval;
}
ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
loff_t *f_pos)
{
ssize_t retval = -ENOMEM; /* value used in "goto out" statements */
if (*f_pos >= MAX_SIZE)
goto out;
if (*f_pos + count > MAX_SIZE)
count = MAX_SIZE - *f_pos;
if (copy_from_user(store + *f_pos + size, buf, count)) {
retval = -EFAULT;
goto out;
}
*f_pos += count;
retval = count;
/* update the size */
// if (size < *f_pos)
size = *f_pos;
out:
return retval;
}
loff_t scull_llseek(struct file *filp, loff_t off, int whence)
{
loff_t newpos;
switch(whence) {
case 0: /* SEEK_SET */
newpos = off;
break;
case 1: /* SEEK_CUR */
newpos = filp->f_pos + off;
break;
case 2: /* SEEK_END */
newpos = size + off;
break;
default: /* can't happen */
return -EINVAL;
}
if (newpos < 0) return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
struct file_operations scull_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.open = scull_open,
.release = scull_release,
};
int scull_init_module(void)
{
int result;
dev_t dev = 0;
/*
* Get a range of minor numbers to work with, asking for a dynamic major
*/
result = alloc_chrdev_region(&dev, scull_minor, 1, "scull");
scull_major = MAJOR(dev);
if (result < 0) {
printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
return result;
}
/* register our device */
cdev_init(&cdev, &scull_fops);
cdev.owner = THIS_MODULE;
cdev.ops = &scull_fops;
result = cdev_add (&cdev, dev, 1);
if (result) {
printk(KERN_WARNING "Error %d adding scull", result);
unregister_chrdev_region(dev, 1);
return result;
}
return 0; /* succeed */
}
void scull_cleanup_module(void)
{
/* cleanup_module is never called if registering failed */
dev_t dev;
cdev_del(&cdev);
dev = MKDEV(scull_major, scull_minor);
unregister_chrdev_region(dev, 1);
}
module_init(scull_init_module);
module_exit(scull_cleanup_module);