Example character device driver for generating large minor numbers

bigdummy.c

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

#define BIGDUMMY_MINOR 65536

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robb Manes");
MODULE_DESCRIPTION("Simulates a dummy device with a pre-defined minor number.");
MODULE_VERSION("0.1");

static int bigdummy_open(struct inode *inode, struct file *file);
static int bigdummy_release(struct inode *inode, struct file *file);
static long bigdummy_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
static ssize_t bigdummy_read(struct file *file, char __user *buf, size_t count, loff_t *offset);
static ssize_t bigdummy_write(struct file *file, const char __user *buf, size_t count, loff_t *offset);

struct bigdummy_cdev {
    struct cdev cdev;
};

struct file_operations bigdummy_fops = {
	.owner		= THIS_MODULE,
	.open		= bigdummy_open,
	.release	= bigdummy_release,
	.unlocked_ioctl	= bigdummy_ioctl,
	.read		= bigdummy_read,
	.write		= bigdummy_write
};

static int majordev;
static struct class *bigdummy_class = NULL;
static struct bigdummy_cdev bigdummy_data[1];

static int bigdummy_open(struct inode *inode, struct file *file)
{
	printk("bigdummy: open not implemented\n");
	return 0;
}

static int bigdummy_release(struct inode *inode, struct file *file)
{
	printk("bigdummy: release not implemented\n");
	return 0;
}

static long bigdummy_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	printk("bigdummy: ioctl not implemented\n");
	return 0;
}

static ssize_t bigdummy_read(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
	printk("bigdummy: read not implemented\n");
	return 0;
}

static ssize_t bigdummy_write(struct file *file, const char __user *buf, size_t count, loff_t *offset)
{
	printk("bigdummy: write not implemented\n");
	return 0;
}

static int __init bigdummy_load(void)
{
	int err;
	dev_t dev;

	printk("Preparing dummy device...\n");
	err = alloc_chrdev_region(&dev, 0, 1, "bigdummy");
	if (err) {
		printk("Failed to load, exiting bigdummy module init...\n");
		return -1;
	}

	majordev = MAJOR(dev);
	bigdummy_class = class_create(THIS_MODULE, "bigdummy");
	cdev_init(&bigdummy_data[0].cdev, &bigdummy_fops);
	bigdummy_data[0].cdev.owner = THIS_MODULE;
	cdev_add(&bigdummy_data[0].cdev, MKDEV(majordev, BIGDUMMY_MINOR), 1);
	device_create(bigdummy_class, NULL, MKDEV(majordev, BIGDUMMY_MINOR), NULL, "bigdummy-%d", 0);
	printk("Dummy device finished initialization.\n");
	return 0;
}

static void __exit bigdummy_unload(void)
{
	return;
}

module_init(bigdummy_load);
module_exit(bigdummy_unload);

Makefile

obj-m += bigdummy.o

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean