add task 9

README.md

@@ -230,6 +230,58 @@ ls -l /sys/kernel/debug/eudyptula/
  * [Chapitre 3, Linux Device Drivers, 3rd Edition](https://lwn.net/Kernel/LDD3/)
  * [Jiffies, Linux Kernel Development 2nd Edition](https://litux.nl/mirror/kerneldevelopment/0672327201/ch10lev1sec3.html)
 
+### Tache 9
+
+Idem que la tache 8 pour tester les sémaphores.
+
+```bash
+ls -l /sys/eudyptula/
+# total 0
+# -rw-r--r-- 1 root root 4096 Jan 23 18:42 foo
+# -rw-rw-rw- 1 root root 4096 Jan 23 18:42 id
+# -r--r--r-- 1 root root 4096 Jan 23 18:42 jiffies
+echo pouet > /sys/eudyptula/foo
+cat /sys/eudyptula/foo
+# pouet
+echo coucou ! > /sys/eudyptula/foo
+cat /sys/eudyptula/foo
+# coucou !
+cat /sys/eudyptula/id
+# pouetpouet
+echo -n congruent > /sys/eudyptula/id
+echo $?
+# 0
+echo pouet > /sys/eudyptula/id
+# bash: echo: write error: Invalid argument
+echo $?
+# 1
+echo pouet > /sys/eudyptula/jiffies
+# bash: /sys/eudyptula/jiffies: Permission denied
+cat /sys/eudyptula/jiffies
+# 4344413015
+cat /sys/eudyptula/jiffies
+# 4344413465
+echo pouet > /sys/eudyptula/foo &
+cat /sys/eudyptula/foo
+# cat: /sys/eudyptula/foo: Invalid argument
+cat /sys/eudyptula/foo &
+cat /sys/eudyptula/foo &
+echo pouet > /sys/eudyptula/foo
+# bash: echo: write error: Invalid argument
+rmmod sysfs
+ls -l /sys/eudyptula/
+# ls: cannot access '/sys/eudyptula/': No such file or directory
+```
+
+ * [The zen of kobjects](https://lwn.net/Articles/51437/) : un peu vieux, certaines fonctions pas
+   à jour
+ * [kobjects and sysfs](https://lwn.net/Articles/54651/) : idem
+ * [Everything you never wanted to know about kobjects, ksets, and
+   ktypes](https://docs.kernel.org/core-api/kobject.html) (documentation noyau)
+ * [Exemple de code pour
+   `kobject`](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kobject)
+ * [Chapitre 14, Linux Device Drivers, 3rd Edition](https://lwn.net/Kernel/LDD3/)
+
 ## Informations diverses
 
 Je liste dans cette section quelques informations que j'ai pu découvrir en

task_09/Makefile

@@ -0,0 +1,9 @@
+obj-m += sysfs.o
+
+PWD := $(CURDIR)
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

task_09/sysfs.c

@@ -0,0 +1,189 @@
+// 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.");