mydev.c

#include <linux/module.h>
#include <linux/device.h>
#include <linux/err.h>

int value = 0;

static ssize_t attr_store(struct device *dev,
		struct device_attribute *attr,
		const char *buf, size_t count)
{

    value = simple_strtoul(buf, NULL, 10);
    printk("value:%d\n", value);
    return count;
}

static ssize_t attr_show(struct device *dev,
		struct device_attribute *attr,
		char *buf)
{
        int val=0;
        val=sprintf(buf, "%d\n",value);
        printk("%d\n", val);
        return val;
}

static struct class *mydev_class;
static struct device *dev;

static DEVICE_ATTR(data, 0644, attr_show, attr_store);

static int __init init_mydev(void)
{
	int ret = 0;
	printk("Init my dev\n");
	mydev_class = class_create(THIS_MODULE, "mydev_class");
	if(IS_ERR(mydev_class)) {
		ret = PTR_ERR(mydev_class);
		printk(KERN_ALERT "Failed to create class.\n");
		return ret;
	}

	dev = device_create(mydev_class, NULL, MKDEV(100,0), NULL, "dev");
	if(IS_ERR(dev)) {
		ret = PTR_ERR(dev);
		printk(KERN_ALERT "Failed to create device.\n");
		return ret;
	}

	ret = device_create_file(dev, &dev_attr_data);
	if(ret < 0) {
		printk(KERN_ALERT "Failed to create attribute file.\n");
		return ret;
	}
	return ret;
}


static void __exit cleanup_mydev(void)
{
	printk("Cleanup my dev\n");
	device_remove_file(dev, &dev_attr_data);
	device_destroy(mydev_class, MKDEV(100, 0));
	class_destroy(mydev_class);
}


module_init(init_mydev);
module_exit(cleanup_mydev);

MODULE_LICENSE("GPL");