08 done

08/Makefile

@@ -0,0 +1,8 @@
+obj-m += main.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

08/main.c

@@ -1,4 +1,3 @@
-Little Penguin Linux Kernel Development
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -28,24 +27,35 @@ static struct miscdevice myfd_device = {
 };
 
 char str[PAGE_SIZE];
+DEFINE_MUTEX(rw_lock);
 
 static int __init myfd_init(void)
 {
-	int retval;
+	mutex_init(&rw_lock);
+	return misc_register(&myfd_device);
+}
 
-	retval = misc_register(&myfd_device);
-	return 1;
+static void __exit myfd_cleanup(void)
+{
+	misc_deregister(&myfd_device);
 }
 
 ssize_t myfd_read(struct file *fp, char __user *user, size_t size, loff_t *offs)
 {
+	ssize_t retval;
 	size_t len;
+	char *tmp;
 	
+	mutex_lock(&rw_lock);
 	len = strlen(str);
-	for (size_t i = 0; i < len / 2; i++) {
-		tmp[i] = str[t];
+	tmp = kmalloc(sizeof(char) * PAGE_SIZE, GFP_KERNEL);
+	for (size_t i = 0,j = len - 1; i < len; i++, j--) {
+		tmp[i] = str[j];
 	}
-	return simple_read_from_buffer(user, size, offs, tmp, i);
+	tmp[len] = 0;
+	retval = simple_read_from_buffer(user, size, offs, tmp, len);
+	mutex_unlock(&rw_lock);
+	return retval;
 }
 
 ssize_t myfd_write(struct file *fp, const char __user *user, size_t size,
@@ -53,8 +63,12 @@ ssize_t myfd_write(struct file *fp, const char __user *user, size_t size,
 {
 	ssize_t res;
 
-	res = simple_write_to_buffer(str, size, offs, user, size) + 1;
-	str[size + 1] = 0x0;
+	if(size >= (PAGE_SIZE - 1))
+		return -EINVAL;
+	mutex_lock(&rw_lock);
+	res = simple_write_to_buffer(str, size, offs, user, size);
+	str[res] = 0x0;
+	mutex_unlock(&rw_lock);
 	return res;
 }