85 lines
2.1 KiB
C
85 lines
2.1 KiB
C
/*
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* sleepy.c -- the writers awake the readers
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*
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* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
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* Copyright (C) 2001 O'Reilly & Associates
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*
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* The source code in this file can be freely used, adapted,
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* and redistributed in source or binary form, so long as an
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* acknowledgment appears in derived source files. The citation
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* should list that the code comes from the book "Linux Device
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* Drivers" by Alessandro Rubini and Jonathan Corbet, published
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* by O'Reilly & Associates. No warranty is attached;
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* we cannot take responsibility for errors or fitness for use.
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*
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* $Id: sleepy.c,v 1.7 2004/09/26 07:02:43 gregkh Exp $
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*/
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/sched.h> /* current and everything */
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#include <linux/kernel.h> /* printk() */
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#include <linux/fs.h> /* everything... */
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#include <linux/types.h> /* size_t */
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#include <linux/wait.h>
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MODULE_LICENSE("Dual BSD/GPL");
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static int sleepy_major = 0;
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static DECLARE_WAIT_QUEUE_HEAD(wq);
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static int flag = 0;
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ssize_t sleepy_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
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{
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printk(KERN_DEBUG "process %i (%s) going to sleep\n",
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current->pid, current->comm);
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wait_event_interruptible(wq, flag != 0);
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flag = 0;
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printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);
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return 0; /* EOF */
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}
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ssize_t sleepy_write (struct file *filp, const char __user *buf, size_t count,
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loff_t *pos)
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{
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printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",
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current->pid, current->comm);
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flag = 1;
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wake_up_interruptible(&wq);
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return count; /* succeed, to avoid retrial */
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}
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struct file_operations sleepy_fops = {
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.owner = THIS_MODULE,
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.read = sleepy_read,
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.write = sleepy_write,
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};
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int sleepy_init(void)
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{
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int result;
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/*
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* Register your major, and accept a dynamic number
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*/
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result = register_chrdev(sleepy_major, "sleepy", &sleepy_fops);
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if (result < 0)
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return result;
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if (sleepy_major == 0)
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sleepy_major = result; /* dynamic */
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return 0;
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}
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void sleepy_cleanup(void)
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{
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unregister_chrdev(sleepy_major, "sleepy");
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}
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module_init(sleepy_init);
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module_exit(sleepy_cleanup);
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