ioctl.c

struct miscdev_data {
    int val;
    char data[64];
};

#define IOCTL_MISCDEV_SET 0x00
#define IOCTL_MISCDEV_GET 0x01

static long mydev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{

	struct miscdev_data data;
 
	memset(&data, 0, sizeof(data));
	switch (cmd) {
	case IOCTL_MISCDEV_SET:
		printk("[%s][%d]\n", __func__, __LINE__);
		copy_from_user(&data, (int __user *)arg, sizeof(data));
		printk("Set data: miscdev_data.val = %d, miscdev_data.data = %s\n", data.val, data.data); 
	   	break;
	case IOCTL_MISCDEV_GET:
		printk("[%s][%d]\n", __func__, __LINE__);
		sprintf(data.data, "Kernel says hi");
		data.val = 3;
		copy_to_user((int __user *)arg, &data, sizeof(data));
		break;
	default:
		break;
	}
	return 0;
}