#include <linux/module.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

#define MAX_BUFSIZE 4096
#define MAX_BUFNUM 4

int flgOpen = 0;
unsigned char memdev_buf0[MAX_BUFNUM][MAX_BUFSIZE];
static int memdev_buflen = 0;


static int __init init_memdev(void);
static void __exit exit_memdev(void);
static int memdev_open(void);
static int memdev_release(void);
static ssize_t memdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos);
static int memdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos);

static struct file_operations memdev_fops = {
	.owner	= THIS_MODULE,
	.open	= memdev_open,
	.release = memdev_release,
	.read 	= memdev_read,
	.write	= memdev_write,
};



static int __init init_memdev(void)
{
	printk("loading memdev...\n");
	register_chrdev(99, "/dev/memdev", &memdev_fops);
}

static void __exit exit_memdev(void)
{
	printk("unloading memdev...\n");
	unregister_chrdev(99, "/dev/memdev");
}

static int memdev_open(void)
{
	flgOpen = 1;
	return 0;
}

static int memdev_release(void)
{
	flgOpen = 0;
	return 0;
}

static ssize_t memdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos)
{
	char *memdev_buf;
	struct inode *inode = fp->f_path.dentry->d_inode;
	unsigned int minor = iminor(inode);
	memdev_buf = memdev_buf0[minor];
	

	if(size >= MAX_BUFSIZE) return 0; /* because of '\0' */

	
	if (copy_from_user(memdev_buf, buf, size)) {
		printk("copy_from_user failed...\n");
		return 0; /* kakikometa data size */
	} else {
		memdev_buflen = size;
		printk(KERN_INFO "copy_from_user succeeded...\n");
		return size;
	}
}

static int memdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{
	char *memdev_buf;
	struct inode *inode = fp->f_path.dentry->d_inode;
	unsigned int minor = iminor(inode);
	memdev_buf = memdev_buf0[minor];

	if (memdev_buflen == 0 ) return 0;
	
	if (copy_to_user(buf, memdev_buf, size)) {
		printk("copy_to_user failed...\n");
		return 0; /* yomikometa data size */
	} else {
		return size;
	}

}

module_init(init_memdev)
module_exit(exit_memdev)