add task 8

README.md

@@ -180,6 +180,56 @@ echo "bonjour12" > /dev/eudyptula
  * [Linux Kernel Labs - Character device drivers](https://linux-kernel-labs.github.io/refs/heads/master/labs/device_drivers.html#read-and-write)
  * [Nihall - Misc character devices](https://nihaal.me/post/misc_char_devices/)
 
+## Tache 8
+
+L'ajout d'une nouvelle string dans le fichier ne supprime l'entièreté du
+contenu du fichier. J'ai testé les sémaphores avec des `msleep`
+(`<linux/delay.h>`) rajouté dans le code. Il est possible de tester en
+décommentant le premier `define`.
+
+```bash
+ls -l /sys/kernel/debug/eudyptula/
+# total 0
+# -rw-rw-r-- 1 root root 0 Jan  9 22:46 foo
+# -rw-rw-rw- 1 root root 0 Jan  9 22:44 id
+# -r--r--r-- 1 root root 0 Jan  9 22:45 jiffies
+echo pouet > /sys/kernel/debug/eudyptula/foo
+cat /sys/kernel/debug/eudyptula/foo
+# pouet
+echo coucou ! > /sys/kernel/debug/eudyptula/foo
+cat /sys/kernel/debug/eudyptula/foo
+# coucou !
+cat /sys/kernel/debug/eudyptula/id
+# pouetpouet
+echo congruent > /sys/kernel/debug/eudyptula/id
+echo $?
+# 0
+echo pouet > /sys/kernel/debug/eudyptula/id
+# bash: echo: write error: Invalid argument
+echo $?
+# 1
+echo pouet > /sys/kernel/debug/eudyptula/jiffies
+# bash: echo: write error: Permission denied
+cat /sys/kernel/debug/eudyptula/jiffies
+# 4345895105
+cat /sys/kernel/debug/eudyptula/jiffies
+# 4345895338
+echo pouet > /sys/kernel/debug/eudyptula/foo &
+cat /sys/kernel/debug/eudyptula/foo
+# cat: /sys/kernel/debug/eudyptula/foo: Invalid argument
+cat /sys/kernel/debug/eudyptula/foo &
+cat /sys/kernel/debug/eudyptula/foo &
+echo pouet > /sys/kernel/debug/eudyptula/foo
+# bash: echo: write error: Invalid argument
+rmmod hello
+ls -l /sys/kernel/debug/eudyptula/
+# ls: cannot access '/sys/kernel/debug/eudyptula/': No such file or directory
+```
+
+ * [DebugFS (Documentation kernel)](https://docs.kernel.org/filesystems/debugfs.html)
+ * [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)
+
 ## Informations diverses
 
 Je liste dans cette section quelques informations que j'ai pu découvrir en

task_08/Makefile

@@ -0,0 +1,9 @@
+obj-m += debugfs.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_08/debugfs.c

@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//#define DEBUG 1
+
+#include <asm/page.h>
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/rwsem.h>
+
+#ifdef DEBUG
+#include <linux/kernel.h>
+#endif
+
+#define BUFFER_LENGTH 10
+
+static struct dentry *folder;
+static struct dentry *id_file;
+static struct dentry *foo_file;
+
+static char *id_msg;
+static char *foo_msg;
+static struct rw_semaphore foo_sem;
+
+static ssize_t id_read(struct file *, char __user *buffer, size_t length, loff_t *offset)
+{
+  int bytes = 0;
+  const char *msg_tmp = id_msg;
+
+  /*
+   * TODO
+	if (!*(msg_tmp + *offset)) {
+		*offset = 0;
+		return 0;
+	}
+  */
+
+	msg_tmp += *offset;
+
+	while (*msg_tmp && bytes < length) {
+		put_user(*(msg_tmp), (buffer + bytes));
+		bytes++;
+		msg_tmp++;
+	}
+
+	*offset += bytes;
+	return bytes;
+}
+
+static ssize_t id_write(struct file *, const char __user *buffer,
+			size_t size, loff_t *)
+{
+	int ret;
+	char *tmp_buffer;
+
+	if (size == 0)
+		return 0;
+
+	tmp_buffer = kzalloc(BUFFER_LENGTH, GFP_KERNEL);
+
+	if (copy_from_user(tmp_buffer, buffer, BUFFER_LENGTH)) {
+		kfree(tmp_buffer);
+		return -EINVAL;
+	}
+
+	*(tmp_buffer + BUFFER_LENGTH - 1) = '\0';
+	pr_info("Test %s-\n", tmp_buffer);
+
+	if (!strcmp(tmp_buffer, "congruent"))
+		ret = BUFFER_LENGTH;
+	else
+		ret = -EINVAL;
+
+	kfree(tmp_buffer);
+	return ret;
+}
+
+static const struct file_operations id_fops = {
+	.owner = THIS_MODULE,
+	.read = id_read,
+	.write = id_write,
+};
+
+static ssize_t foo_read(struct file *, char __user *buffer, size_t count, loff_t *offset)
+{
+  int bytes = -EINVAL;
+  int tmp_len = strlen(foo_msg);
+
+  if (*offset > tmp_len) bytes = -EFAULT;
+  else if (down_read_trylock(&foo_sem))
+  {
+    char *tmp_str = foo_msg + *offset;
+    tmp_len = strlen(tmp_str);
+
+    bytes = tmp_len > count ? count : tmp_len;
+    if (copy_to_user(buffer, tmp_str, bytes)) bytes = -EFAULT;
+    else *offset += bytes;
+#ifdef DEBUG
+    msleep(5000);
+#endif
+    up_read(&foo_sem);
+  }
+
+  return bytes;
+}
+
+static ssize_t foo_write(struct file *, const char __user *buffer,
+			size_t count, loff_t * offset)
+{
+  int bytes = -EINVAL;
+
+  if ((*offset + count) > PAGE_SIZE) bytes = -EFAULT;
+  else if (down_write_trylock(&foo_sem))
+  {
+    bytes = count;
+    if (copy_from_user(foo_msg, buffer, bytes)) bytes = -EINVAL;
+#ifdef DEBUG
+    msleep(5000);
+#endif
+    up_write(&foo_sem);
+  }
+
+  return bytes;
+}
+
+static const struct file_operations foo_fops = {
+	.owner = THIS_MODULE,
+	.read = foo_read,
+	.write = foo_write,
+};
+
+static int __init my_init(void)
+{
+  init_rwsem(&foo_sem);
+  id_msg = kmalloc(12, GFP_KERNEL);
+  foo_msg = kmalloc(PAGE_SIZE, GFP_KERNEL);
+  strcpy(id_msg, "pouetpouet\n");
+	pr_info("Coucou le gens !!!!\n");
+
+  folder = debugfs_create_dir("eudyptula", NULL);
+  id_file = debugfs_create_file("id", 0666, folder, NULL, &id_fops);
+  debugfs_create_u64("jiffies", 0444, folder, &jiffies_64);
+  foo_file = debugfs_create_file("foo", 0664, folder, NULL, &foo_fops);
+  
+	return 0;
+}
+
+static void __exit my_exit(void)
+{
+  debugfs_remove_recursive(folder);
+  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 debugfs.");