yesmod.c

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("qookie");

static int device_open(struct inode *, struct file *);
static int device_release(struct inode *, struct file *);
static ssize_t device_read(struct file *, char *, size_t, loff_t *);
static ssize_t device_write(struct file *, const char *, size_t, loff_t *);

static struct file_operations fops = {
	read: device_read,
	write: device_write,
	open: device_open,
	release: device_release
};

#define BUF_SIZ 8192

static char yes_buf[BUF_SIZ];

static int major;
#define DEV_NAME "yes"

static int yesmod_init(void) {
	size_t i;

	printk(KERN_INFO "yesmod: initializing\n");
	for (i = 0; i < BUF_SIZ; i += 2) {
		yes_buf[i] = 'y';
		yes_buf[i + 1] = '\n';
	}

	major = register_chrdev(0, DEV_NAME, &fops);

	if (major < 0) {
		printk(KERN_ALERT "yesmod: registering char device failed with %d\n", major);
		return major;
	}

	printk(KERN_INFO "yesmod: to use the device, run:\n");
	printk(KERN_INFO "yesmod: 'mknod /dev/" DEV_NAME " c %d 0'\n", major);

	return 0;
}

static void yesmod_cleanup(void) {
	printk(KERN_INFO "yesmod: deinitializing\n");
	unregister_chrdev(major, DEV_NAME);
}

static int device_open(struct inode *inode, struct file *file) {
	try_module_get(THIS_MODULE);
	return 0;
}

static int device_release(struct inode *inode, struct file *file) {
	module_put(THIS_MODULE);
	return 0;
}

static ssize_t device_read(struct file *filp, char *buffer, 
				size_t length, loff_t * offset) {

	int actual = length > BUF_SIZ ? BUF_SIZ : length;
	if (actual & 1) actual--;
	memcpy(buffer, yes_buf, actual);
	return actual;
}

static ssize_t device_write(struct file *filp, const char *buff, size_t len, loff_t * off) {
	return -EINVAL;
}

module_init(yesmod_init);
module_exit(yesmod_cleanup);