/* * sleepy.c -- the writers awake the readers * * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet * Copyright (C) 2001 O'Reilly & Associates * * The source code in this file can be freely used, adapted, * and redistributed in source or binary form, so long as an * acknowledgment appears in derived source files.  The citation * should list that the code comes from the book "Linux Device * Drivers" by Alessandro Rubini and Jonathan Corbet, published * by O'Reilly & Associates.   No warranty is attached; * we cannot take responsibility for errors or fitness for use. * * $Id: sleepy.c,v 1.13 2001/07/18 22:28:16 rubini Exp $ */#ifndef __KERNEL__#  define __KERNEL__#endif#ifndef MODULE#  define MODULE#endif#include <linux/module.h>#include <linux/sched.h>  /* current and everything */#include <linux/kernel.h> /* printk() */#include <linux/fs.h>     /* everything... */#include <linux/types.h>  /* size_t */#include "sysdep.h"int sleepy_major=0;DECLARE_WAIT_QUEUE_HEAD(wq);ssize_t sleepy_read (struct file *filp, char *buf, size_t count, loff_t *pos){    printk(KERN_DEBUG "process %i (%s) going to sleep\n",           current->pid, current->comm);    interruptible_sleep_on(&wq);    printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);    return 0; /* EOF */}ssize_t sleepy_write (struct file *filp, const char *buf, size_t count,		loff_t *pos){    printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",           current->pid, current->comm);    wake_up_interruptible(&wq);    return count; /* succeed, to avoid retrial */}#ifdef LINUX_20 /* wrappers for 2.0 */int sleepy_read_20 (struct inode *ino, struct file *f, char *buf, int count){    return (int)sleepy_read(f, buf, count, &f->f_pos);}int sleepy_write_20 (struct inode *ino, struct file *f, const char *b, int c){    return (int)sleepy_write(f, b, c, &f->f_pos);}#define sleepy_read sleepy_read_20#define sleepy_write sleepy_write_20#endif  /* LINUX_20 */struct file_operations sleepy_fops = {    read:  sleepy_read,    write: sleepy_write,};int sleepy_init(void){    int result;    SET_MODULE_OWNER(&sleepy_fops);    /*     * Register your major, and accept a dynamic number     */    result = register_chrdev(sleepy_major, "sleepy", &sleepy_fops);    if (result < 0) return result;    if (sleepy_major == 0) sleepy_major = result; /* dynamic */    return 0;}void sleepy_cleanup(void){    unregister_chrdev(sleepy_major, "sleepy");}module_init(sleepy_init);module_exit(sleepy_cleanup);