#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <asm/uaccess.h>
#define DEVICE_NAME "chardev"
static int chardev_open(struct inode *inodp, struct file *filp);
static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos);
static ssize_t chardev_write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos);
static int chardev_fasync(int fd, struct file *filp, int mode);
static int chardev_release(struct inode *inodp, struct file *filp);
static struct file_operations chardev_fops = {
.open = chardev_open,
.read = chardev_read,
.write = chardev_write,
.fasync = chardev_fasync,
.release = chardev_release,
};
static struct fasync_struct *async = NULL;
static struct semaphore sem;
static struct cdev *cdevp;
static dev_t devno;
static char buffer[8192];
static int chardev_open(struct inode *inodp, struct file *filp)
{
return 0;
}
static ssize_t chardev_read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos)
{
if (down_interruptible(&sem))
goto err;
count = strlen(buffer);
copy_to_user(buff, buffer, count);
up(&sem);
return count;
err:
return -ERESTARTSYS;
}
static ssize_t chardev_write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos)
{
if (down_interruptible(&sem))
goto err;
memset(buffer, '\0', sizeof(buffer));
copy_from_user(buffer, buff, count);
up(&sem);
if (async)
kill_fasync(&async, SIGIO, POLL_IN);
return count;
err:
return -ERESTARTSYS;
}
static int chardev_fasync(int fd, struct file *filp, int mode)
{
return fasync_helper(fd, filp, mode, &async);
}
static int chardev_release(struct inode *inodp, struct file *filp)
{
return chardev_fasync(-1, filp, 0);
}
static int __init chardev_init(void)
{
int ret;
ret = alloc_chrdev_region(&devno, 0, 1, DEVICE_NAME);
if (ret < 0)
goto out;
init_MUTEX(&sem);
cdevp = cdev_alloc();
if (!cdevp)
goto alloc_err;
cdev_init(cdevp, &chardev_fops);
ret = cdev_add(cdevp, devno, 1);
if (!ret)
goto out;
alloc_err:
unregister_chrdev_region(devno, 1);
out:
return ret;
}
static void __exit chardev_exit(void)
{
cdev_del(cdevp);
unregister_chrdev_region(devno, 1);
}
MODULE_LICENSE("GPL");
module_init(chardev_init);
module_exit(chardev_exit);
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