From c4abffb96e4ac41ee136d518ed2e8cad2a4cc819 Mon Sep 17 00:00:00 2001
From: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Date: Sun, 6 Dec 2009 18:22:25 -0200
Subject: [PATCH 1/1] First character device.

This version uses a kobject_put in an error path, which students may not know
about yet.
---
 Makefile | 11 +++++++++
 helloc.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 Makefile
 create mode 100644 helloc.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..76d1323
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,11 @@
+ifneq ($(KERNELRELEASE),)
+	obj-m := helloc.o
+else
+	KERNELDIR ?= /lib/modules/$(shell uname -r)/build
+	PWD := $(shell pwd)
+default:
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
+
+clean:
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
+endif
diff --git a/helloc.c b/helloc.c
new file mode 100644
index 0000000..4d99fcb
--- /dev/null
+++ b/helloc.c
@@ -0,0 +1,68 @@
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/cdev.h>
+#include <asm/uaccess.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>");
+MODULE_DESCRIPTION("A hello world char device");
+MODULE_VERSION("1.0.0");
+
+static char helloc_message[] = "hello, world\n";
+
+static ssize_t helloc_read(struct file *filp, char __user *buf, size_t len,
+			   loff_t *pos)
+{
+	int r;
+	if (*pos >= sizeof(helloc_message))
+		return 0;
+	if (len > sizeof(helloc_message) - *pos)
+		len = sizeof(helloc_message) - *pos;
+	r = copy_to_user(buf, helloc_message + *pos, len);
+	if (r)
+		return -EFAULT;
+	*pos += len;
+	return len;
+}
+
+static struct file_operations helloc_fops = {
+	.owner = THIS_MODULE,
+	.read = helloc_read,
+};
+
+static dev_t dev;
+static struct cdev *cdev;
+
+static int __init helloc_init(void)
+{
+	int r;
+	r = alloc_chrdev_region(&dev, 0, 1, "helloc");
+	if (r)
+		goto out_region;
+	r = -ENOMEM;
+	printk(KERN_INFO "Allocated major number %d\n", MAJOR(dev));
+	cdev = cdev_alloc();
+	if (!cdev)
+		goto out_alloc;
+	cdev->owner = THIS_MODULE;
+	cdev->ops = &helloc_fops;
+	r = cdev_add(cdev, dev, 1);
+	if (r)
+		goto out_add;
+	return 0;
+out_add:
+	kobject_put(&cdev->kobj);
+out_alloc:
+	unregister_chrdev_region(dev, 1);
+out_region:
+	return r;
+}
+
+static void __exit helloc_exit(void)
+{
+	cdev_del(cdev);
+	unregister_chrdev_region(dev, 1);
+}
+
+module_init(helloc_init);
+module_exit(helloc_exit);
-- 
2.20.1