// SPDX-License-Identifier: GPL-2.0

#define DEBUG 1

#include <asm/page.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/rwsem.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/sysfs.h>

#ifdef DEBUG
#include <linux/delay.h>
#endif

#define BUFFER_LENGTH 10

// représente un dossier sur sysfs
static struct kobject eudyptula;

// représente un fichier sur sysfs
static struct attribute id_file = {
	.name = "id",
	.mode = 0666
};

static struct attribute jiffies_file = {
	.name = "jiffies",
	.mode = 0444
};

static struct attribute foo_file = {
	.name = "foo",
	.mode = 0644
};

static char *id_msg;
static char *foo_msg;
static struct rw_semaphore foo_sem;

/*
 * fonctions pour pouvoir lire et écrire dans les fichiers. elles sont ici
 * découpées pour mieux se rendre compte. Il faut cependant les appeler depuis
 * les fonctions se trouvant plus bas.
 */

static ssize_t id_read(char *buffer)
{
	return sysfs_emit(buffer, id_msg);
}

static ssize_t id_write(const char *buffer, size_t size)
{
	int ret = -EINVAL;

	if (!strcmp(buffer, "congruent"))
		ret = size;

	return ret;
}

static ssize_t jiffies_read(char *buffer)
{
	return sprintf(buffer, "%lld\n", jiffies_64);
}

static ssize_t foo_read(char *buffer)
{
	int ret = -EINVAL;

	if (down_read_trylock(&foo_sem)) {
		ret = sysfs_emit(buffer, foo_msg);
#ifdef DEBUG
		msleep(5000);
#endif
		up_read(&foo_sem);
	}

	return ret;
}

static ssize_t foo_write(const char *buffer, size_t count)
{
	int ret = -EINVAL;

	if (down_write_trylock(&foo_sem)) {
		ret = strscpy(foo_msg, buffer, count + 1);
#ifdef DEBUG
		msleep(5000);
#endif
		up_write(&foo_sem);
	}

	return ret;
}

/*
 * fonctions utilisées pour lire et écrire dans les attributes. Elles sont
 * mises dans une structure sysfs_ops et mis à l'initialisation du kobject via
 * un ktype.
 */

ssize_t show(struct kobject *kobj, struct attribute *attr, char *buffer)
{
	ssize_t ret = 0;

	if (!strcmp(attr->name, "id"))
		ret = id_read(buffer);
	else if (!strcmp(attr->name, "jiffies"))
		ret = jiffies_read(buffer);
	else if (!strcmp(attr->name, "foo"))
		ret = foo_read(buffer);
	else
		pr_info("keske tu essaies de lire ?!");

	return ret;
}

ssize_t store(struct kobject *kobj, struct attribute *attr, const char *buffer,
	      size_t len)
{
	ssize_t ret = 0;

	if (!strcmp(attr->name, "id"))
		ret = id_write(buffer, len);
	else if (!strcmp(attr->name, "foo"))
		ret = foo_write(buffer, len);
	else
		pr_info("keske tu essaies d'ecrire ?!");

	return ret;
}

static const struct sysfs_ops my_ops = {
	.show = &show,
	.store = &store,
};

static const struct kobj_type my_type = {
	.sysfs_ops = &my_ops,
};

static int __init my_init(void)
{
	pr_info("Coucou le gens !!!!\n");

	if (!memset(&eudyptula, 0, sizeof(struct kobject)))
		return -ENOMEM;

	if (kobject_init_and_add(&eudyptula, &my_type, NULL, "eudyptula")) {
		kobject_put(&eudyptula);
		return -ENOMEM;
	}

	if (sysfs_create_file(&eudyptula, &id_file)
	    || sysfs_create_file(&eudyptula, &jiffies_file)
	    || sysfs_create_file(&eudyptula, &foo_file)) {
		kobject_put(&eudyptula);
		return -ENOMEM;
	}

	init_rwsem(&foo_sem);
	id_msg = kmalloc(12, GFP_KERNEL);
	foo_msg = kmalloc(PAGE_SIZE, GFP_KERNEL);
	strscpy(id_msg, "pouetpouet\n", 12);

	return 0;
}

static void __exit my_exit(void)
{
	sysfs_remove_file(&eudyptula, &id_file);
	sysfs_remove_file(&eudyptula, &jiffies_file);
	sysfs_remove_file(&eudyptula, &foo_file);
	kobject_put(&eudyptula);
	kfree(id_msg);
	kfree(foo_msg);
	pr_info("Tschuss !!!\n");
}

module_init(my_init);
module_exit(my_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("rick <rick@gnous.eu>");
MODULE_DESCRIPTION("Module pour tester le sysfs.");