#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <asm/io.h>

struct file_operations fops ;
static int major ;

static int my_open(struct inode *inode, struct file *file)
{
	int i ;
	void *data_ptr ;
	struct page *page ;
	printk("I am in my_open\n") ;
	data_ptr = (void *) __get_free_pages(GFP_KERNEL, 4) ;
	if (data_ptr == NULL)
	{	
		printk("__get_free_pages failed\n") ;		
		return -1 ;
	}
	else
	{
		printk("__get_free_pages successful data_ptr = %ld\n", (unsigned long)data_ptr) ;
	}

	for (i = 0 ; i < 16 ; i++)
	{
		page = virt_to_page(data_ptr + PAGE_SIZE * i) ; 
		set_bit(PG_reserved, &page->flags) ;
	}	

	strcpy((char *)data_ptr, "HelloWorld") ;

	file->private_data = data_ptr ;
	return 0 ;
}

static int my_close(struct inode *inode, struct file *file)
{
	int i ;
	struct page *page ;
	unsigned long data_ptr = (unsigned long)file->private_data ;
	printk("I am in my_close\n") ;
	printk("%s data_ptr = %ld\n", (char *)data_ptr, data_ptr) ;

	for (i = 0 ; i < 16 ; i++)
	{
		page = virt_to_page(data_ptr + PAGE_SIZE * i) ; 
		clear_bit(PG_reserved, &page->flags) ;
	}	
	free_pages(data_ptr, 4) ;
	return 0 ;
}

static int my_mmap(struct file *file, struct vm_area_struct *vma)
{
	void *data_ptr = (void *)file->private_data ;
	printk("I am in my_mmap\n") ;
	printk("data_ptr = %ld\n", (unsigned long) data_ptr) ;

	if (remap_page_range(vma, vma->vm_start, virt_to_phys(data_ptr), (vma->vm_end - vma->vm_start), vma->vm_page_prot)) 
	{
		printk("remap_page_range failed\n") ;	
		return -1 ;
	}
	return 0 ;
}

int init_module(void)
{
	printk("I am in init_module\n") ;

	major = register_chrdev(0, "mydriver", &fops) ;
	if(major == -1)
	{
		printk("register_chrdev failed\n") ;
		return -1 ;
	}
	printk("module is registered with major no = %d\n", major) ;
	return 0 ;
}

void cleanup_module(void)
{
	printk("I am in cleanup_module\n") ;
	unregister_chrdev(major, "mydriver") ;
}

struct file_operations fops = 
{
	.open = my_open,
	.release = my_close, 
	.mmap = my_mmap,
} ;