1 files changed, 84 insertions, 0 deletions
diff --git a/misc-modules/sleepy.c b/misc-modules/sleepy.c
new file mode 100644
index 0000000..33c7fc3
--- /dev/null
+++ b/misc-modules/sleepy.c
@@ -0,0 +1,84 @@
+/*
+ * 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 1.7 2004/09/26 07:02:43 gregkh Exp $
+ */
+
+#include <linux/module.h>
+#include <linux/init.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 <linux/wait.h>
+
+MODULE_LICENSE("Dual BSD/GPL");
+
+static int sleepy_major = 0;
+
+static DECLARE_WAIT_QUEUE_HEAD(wq);
+static int flag = 0;
+
+ssize_t sleepy_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
+{
+	printk(KERN_DEBUG "process %i (%s) going to sleep\n",
+			current->pid, current->comm);
+	wait_event_interruptible(wq, flag != 0);
+	flag = 0;
+	printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);
+	return 0; /* EOF */
+}
+
+ssize_t sleepy_write (struct file *filp, const char __user *buf, size_t count,
+		loff_t *pos)
+{
+	printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",
+			current->pid, current->comm);
+	flag = 1;
+	wake_up_interruptible(&wq);
+	return count; /* succeed, to avoid retrial */
+}
+
+
+struct file_operations sleepy_fops = {
+	.owner = THIS_MODULE,
+	.read =  sleepy_read,
+	.write = sleepy_write,
+};
+
+
+int sleepy_init(void)
+{
+	int result;
+
+	/*
+	 * 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);
+