memory.c

/* Necessary includes for device drivers */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
//#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/uaccess.h>

MODULE_LICENSE("Dual BSD/GPL");
/* Declaration of memory.c functions */
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf,
size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, const char *buf,
size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);

/* Structure that declares the usual file */
/* access functions */
struct file_operations memory_fops = {
	read: memory_read,
	write: memory_write,
	open: memory_open,
	release: memory_release
};

/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);

/* Global variables of the driver */
/* Major number */
int memory_major = 60;

/* Buffer to store data */
char *memory_buffer;

int memory_init(void) 
{
	int result;
	/* Registering device */
	result = register_chrdev(memory_major, "memory", &memory_fops);
	if (result < 0) 
	{
		printk("<1>memory: cannot obtain major number %d\n", memory_major);
		return result;
	}
	/* Allocating memory for the buffer */
	memory_buffer = kmalloc(4, GFP_KERNEL);
	if (!memory_buffer) 
	{
		result = -ENOMEM;
		goto fail;
	}
	/*Set buffer to 0 by default */
	memset(memory_buffer, 0, 1);
	printk("<1>Inserting memory module\n");
	return 0;
	fail:
	memory_exit();
	return result;
}


void memory_exit(void) 
{
	/* Freeing the major number */
	unregister_chrdev(memory_major, "memory");
	/* Freeing buffer memory */
	if (memory_buffer)
	{
		kfree(memory_buffer);
	}
	printk("<1>Removing memory module\n");
}


int memory_open(struct inode *inode, struct file *filp) 
{
	/* Success */
	return 0;
}

int memory_release(struct inode *inode, struct file *filp) 
{
	/* Success */
	return 0;
}

ssize_t memory_read(struct file *filp, char *buf,size_t count, loff_t *f_pos)
{
	/* Changing reading position as best suits */
	if (*f_pos == 0) 
	{
		*f_pos+=1;
		/* Transfering data to user space */
		copy_to_user(buf,memory_buffer,4);
		return 4;
	} 
	else 
	{
		return 0;
	}
}

ssize_t memory_write( struct file *filp, const char *buf, size_t count, loff_t *f_pos) {
	copy_from_user(memory_buffer,buf,4);
	return 4;
}