void complete(struct completion *x)
{
 unsigned long flags;

 spin_lock_irqsave(&x->wait.lock, flags);
 x->done++;
 __wake_up_common(&x->wait, TASK_NORMAL, 1, 0, NULL);
 spin_unlock_irqrestore(&x->wait.lock, flags);
}

#include <linux/module.h>
#include <linux/init.h>

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/completion.h>

MODULE_LICENSE("GPL");

static int complete_major=250;
DECLARE_COMPLETION(comp);

ssize_t complete_read(struct file *filp,char __user *buf,size_t count,loff_t *pos)
{
 printk(KERN_ERR "process %i (%s) going to sleep\n",current->pid,current->comm);
 wait_for_completion(&comp);
 printk(KERN_ERR "awoken %i (%s)\n",current->pid,current->comm);
 return 0;
}

ssize_t complete_write(struct file *filp,const char __user *buf,size_t count,loff_t *pos)
{
 printk(KERN_ERR "process %i (%s) awakening the readers...\n",current->pid,current->comm);
 complete(&comp);
 return count;
}

struct file_operations complete_fops={
 .owner=THIS_MODULE,
 .read=complete_read,
 .write=complete_write,
};

int complete_init(void)
{
 int result;
 result=register_chrdev(complete_major,"complete",&complete_fops);
 if(result<0)
  return result;
 if(complete_major==0)
  complete_major=result;
 return 0;
}
void complete_cleanup(void)
{
 unregister_chrdev(complete_major,"complete");
}
module_init(complete_init);
module_exit(complete_cleanup);