From: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Date: Tue, 8 Dec 2009 09:04:36 +0000 (-0200)
Subject: Added comments about our code.
X-Git-Url: http://git.cascardo.info/?p=cascardo%2Fkernel%2Fsamples%2F02.char%2F.git;a=commitdiff_plain;h=dc644997294da4e07cbb01ecc2598f075b7495bf

Added comments about our code.
---

diff --git a/helloc.c b/helloc.c
index 0a7cf40..0db07e3 100644
--- a/helloc.c
+++ b/helloc.c
@@ -1,6 +1,9 @@
 #include <linux/module.h>
+/* Needed for struct file_operations and others */
 #include <linux/fs.h>
+/* Needed for struct cdev */
 #include <linux/cdev.h>
+/* Needed for copying to/from user space */
 #include <asm/uaccess.h>
 
 MODULE_LICENSE("GPL");
@@ -8,51 +11,67 @@ MODULE_AUTHOR("Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>");
 MODULE_DESCRIPTION("A hello world char device");
 MODULE_VERSION("1.0.0");
 
+/* Message buffer we send to upstream */
 static char helloc_message[] = "hello, world\n";
 
+/* our read function writes our message to the user buffer */
 static ssize_t helloc_read(struct file *filp, char __user *buf, size_t len,
 			   loff_t *pos)
 {
 	int r;
+	/* do not read pass through the size of the message */
 	if (*pos >= sizeof(helloc_message))
+	/* return end of file */
 		return 0;
+	/* if len is bigger than the rest of the message, clamp it */
 	if (len > sizeof(helloc_message) - *pos)
 		len = sizeof(helloc_message) - *pos;
+	/* copy message to user space and return error if it fails */
 	r = copy_to_user(buf, helloc_message + *pos, len);
 	if (r)
 		return -EFAULT;
+	/* update the file position */
 	*pos += len;
 	return len;
 }
 
+/* we only implement read */
 static struct file_operations helloc_fops = {
 	.owner = THIS_MODULE,
 	.read = helloc_read,
 };
 
+/* the device number and the char device struct */
 static dev_t dev;
 static struct cdev *cdev;
 
 static int __init helloc_init(void)
 {
 	int r;
+	/* allocate any major number with only one minor */
 	r = alloc_chrdev_region(&dev, 0, 1, "helloc");
 	if (r)
 		goto out_region;
 	r = -ENOMEM;
+	/* print the major number allocated so we can create our device node */
 	printk(KERN_INFO "Allocated major number %d\n", MAJOR(dev));
+	/* allocate the character device struct */
 	cdev = cdev_alloc();
 	if (!cdev)
 		goto out_alloc;
+	/* set the module owner and the file operations of our chardev */
 	cdev->owner = THIS_MODULE;
 	cdev->ops = &helloc_fops;
+	/* register the chardev to the system */
 	r = cdev_add(cdev, dev, 1);
 	if (r)
 		goto out_add;
 	return 0;
 out_add:
+	/* release memory allocated to the cdev device */
 	kfree(cdev);
 out_alloc:
+	/* release the device number allocated */
 	unregister_chrdev_region(dev, 1);
 out_region:
 	return r;
@@ -60,7 +79,9 @@ out_region:
 
 static void __exit helloc_exit(void)
 {
+	/* remove the chardev from the system */
 	cdev_del(cdev);
+	/* release the device number allocated */
 	unregister_chrdev_region(dev, 1);
 }