From 2fa0b3e1817228b3d23741a06ed044cdf66ccc88 Mon Sep 17 00:00:00 2001
From: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Date: Tue, 8 Dec 2009 10:49:25 -0200
Subject: [PATCH] Implemented open/release with multiple devices.

---
 helloc.c | 52 +++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 43 insertions(+), 9 deletions(-)

diff --git a/helloc.c b/helloc.c
index 0db07e3..8c085f3 100644
--- a/helloc.c
+++ b/helloc.c
@@ -5,6 +5,7 @@
 #include <linux/cdev.h>
 /* Needed for copying to/from user space */
 #include <asm/uaccess.h>
+#include <linux/slab.h>
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>");
@@ -12,22 +13,53 @@ 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";
+static char hello_message[] = "hello, world\n";
+static char goodbye_message[] = "goodbye, world\n";
+
+struct message {
+	char *text;
+	size_t len;
+};
+
+static int helloc_open(struct inode *ino, struct file *filp)
+{
+	struct message *msg;
+	printk(KERN_INFO "Opened file with minor %d\n", iminor(ino));
+	msg = kmalloc(sizeof(struct message), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+	if (iminor(ino) == 0) {
+		msg->text = hello_message;
+		msg->len = sizeof(hello_message);
+	} else {
+		msg->text = goodbye_message;
+		msg->len = sizeof(goodbye_message);
+	}
+	filp->private_data = msg;
+	return 0;
+}
+
+static int helloc_release(struct inode *ino, struct file *filp)
+{
+	kfree(filp->private_data);
+	return 0;
+}
 
 /* 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;
+	struct message *msg = filp->private_data;
 	/* do not read pass through the size of the message */
-	if (*pos >= sizeof(helloc_message))
+	if (*pos >= msg->len)
 	/* 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;
+	if (len > msg->len - *pos)
+		len = msg->len - *pos;
 	/* copy message to user space and return error if it fails */
-	r = copy_to_user(buf, helloc_message + *pos, len);
+	r = copy_to_user(buf, msg->text + *pos, len);
 	if (r)
 		return -EFAULT;
 	/* update the file position */
@@ -38,6 +70,8 @@ static ssize_t helloc_read(struct file *filp, char __user *buf, size_t len,
 /* we only implement read */
 static struct file_operations helloc_fops = {
 	.owner = THIS_MODULE,
+	.open = helloc_open,
+	.release = helloc_release,
 	.read = helloc_read,
 };
 
@@ -49,7 +83,7 @@ static int __init helloc_init(void)
 {
 	int r;
 	/* allocate any major number with only one minor */
-	r = alloc_chrdev_region(&dev, 0, 1, "helloc");
+	r = alloc_chrdev_region(&dev, 0, 2, "helloc");
 	if (r)
 		goto out_region;
 	r = -ENOMEM;
@@ -63,7 +97,7 @@ static int __init helloc_init(void)
 	cdev->owner = THIS_MODULE;
 	cdev->ops = &helloc_fops;
 	/* register the chardev to the system */
-	r = cdev_add(cdev, dev, 1);
+	r = cdev_add(cdev, dev, 2);
 	if (r)
 		goto out_add;
 	return 0;
@@ -72,7 +106,7 @@ out_add:
 	kfree(cdev);
 out_alloc:
 	/* release the device number allocated */
-	unregister_chrdev_region(dev, 1);
+	unregister_chrdev_region(dev, 2);
 out_region:
 	return r;
 }
@@ -82,7 +116,7 @@ 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);
+	unregister_chrdev_region(dev, 2);
 }
 
 module_init(helloc_init);
-- 
2.20.1