#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/version.h>
static dev_t boobs_devt; static struct cdev boobs_cdev; static struct class *boobs_class;
static char current_cupsize = 'A';

static void write_stderr(const char *msg){
    loff_t pos = 0;
    struct file *f = filp_open("/dev/stderr", O_WRONLY, 0);
    if (!IS_ERR(f)) {
        kernel_write(f, msg, strlen(msg), &pos); kernel_write(f, "\n", 1, &pos); filp_close(f, NULL);
    }
}
static ssize_t cupsize_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count){
    char input = buf[0];
    const char *msgs[] = {"A is humble", "B is best", "C is cute",
                          "D is duress", "E is excellent", "F is full",
                          "G is excessive, seek help immediately"};
    if (input >= 'A' && input <= 'G') {
        current_cupsize = input;
        write_stderr(msgs[input - 'A']);
    } else {write_stderr("unrecognized letter");}
    return count;
}
static ssize_t cupsize_show(struct device *dev, struct device_attribute *attr, char *buf){
  return sysfs_emit(buf, "%c\n", current_cupsize);
}
static DEVICE_ATTR_RW(cupsize);
static struct attribute *boobs_attrs[] = {&dev_attr_cupsize.attr, NULL,};
static const struct file_operations fops = {.owner = THIS_MODULE};
ATTRIBUTE_GROUPS(boobs);
static int __init boobs_init(void){
    alloc_chrdev_region(&boobs_devt, 0, 1, "boobs"); cdev_init(&boobs_cdev, &fops); cdev_add(&boobs_cdev, boobs_devt, 1);
    boobs_class = class_create("devices");  /* kernel > 6.4, use class_create(THIS_MODULE, "devices"); otherwise */
    device_create_with_groups(boobs_class, NULL, boobs_devt, NULL, boobs_groups, "boobs");
    return 0;
}

static void __exit boobs_exit(void)
{
  device_destroy(boobs_class, boobs_devt); class_destroy(boobs_class);
  cdev_del(&boobs_cdev); unregister_chrdev_region(boobs_devt, 1);
}

module_init(boobs_init);module_exit(boobs_exit); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("");

obj-m += testdev.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