#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/proc_fs.h>

#include<linux/sched.h>

#include <asm/uaccess.h>

#include <linux/slab.h>

int len, temp;

static char *msg = 0;

static ssize_t

read_proc (struct file *filp, char __user * buf, size_t count, loff_t * offp)

{

if (count > temp)

{

count = temp;

}

temp = temp - count;

copy_to_user (buf, msg, count);

if (count == 0)

temp = len;

return count;

}

static ssize_t

write_proc (struct file *filp, const char __user * buf, size_t count,

loff_t * offp)

{

if (msg == 0 || count > 100)

{

printk (KERN_INFO " either msg is 0 or count >100\n");

}

// you have to move data from user space to kernel buffer

copy_from_user (msg, buf, count);

len = count;

temp = len;

return count;

}

static const struct file_operations proc_fops = {

.owner = THIS_MODULE,

.read = read_proc,

.write = write_proc,

};

void

create_new_proc_entry (void)

{

proc_create ("userlist", 0666, NULL, &proc_fops);

msg = kmalloc (100 * sizeof (char), GFP_KERNEL);

if (msg == 0)

{

printk (KERN_INFO "why is msg 0 \n");

}

}

int

proc_init (void)

{

create_new_proc_entry ();

return 0;

}

void

proc_cleanup (void)

{

remove_proc_entry ("userlist", NULL);

}

MODULE_LICENSE ("GPL");

module_init (proc_init);

module_exit (proc_cleanup);