From: Brian Maly <bmaly@redhat.com>
Subject: [RHEL5.1 patch] allow creation of null parent devices
Date: Tue, 09 Oct 2007 17:40:59 -0400
Bugzilla: 323771
Message-Id: <470BF56B.4000304@redhat.com>
Changelog: [sound] allow creation of null parent devices


resolves BZ 323771

This patch resolves an ALSA regression discovered today that causes the 
snd_pcm_oss module to fail to load with the following message 
"device_create does not work yet for NULL parents". The ALSA 1.0.14 
update switched from using class_device_create() to device_create() 
while still passing a NULL as the value to the parent argument, being it 
is allowed in newer kernels. This patch provides the needed changes to 
allow devices in classes to have no parent, and removes the warning if 
NULL is passed.

This patch is a backport of:
http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=64bb5d2c116478dba7501d2acf078ed74ba30c1f


It has been tested and resolves the issue.

Brian



--- linux-2.6.18.noarch/drivers/base/core.c.orig	2007-08-08 22:08:11.000000000 -0400
+++ linux-2.6.18.noarch/drivers/base/core.c	2007-10-09 17:06:23.000000000 -0400
@@ -3,6 +3,8 @@
  *
  * Copyright (c) 2002-3 Patrick Mochel
  * Copyright (c) 2002-3 Open Source Development Labs
+ * Copyright (c) 2006 Greg Kroah-Hartman <gregkh@suse.de>
+ * Copyright (c) 2006 Novell, Inc.
  *
  * This file is released under the GPLv2
  *
@@ -340,10 +342,11 @@ int device_add(struct device *dev)
 				  "subsystem");
 		sysfs_create_link(&dev->class->subsys.kset.kobj, &dev->kobj,
 				  dev->bus_id);
-
-		sysfs_create_link(&dev->kobj, &dev->parent->kobj, "device");
-		class_name = make_class_name(dev->class->name, &dev->kobj);
-		sysfs_create_link(&dev->parent->kobj, &dev->kobj, class_name);
+		if (parent) {
+			sysfs_create_link(&dev->kobj, &dev->parent->kobj, "device");
+			class_name = make_class_name(dev->class->name, &dev->kobj);
+			sysfs_create_link(&dev->parent->kobj, &dev->kobj, class_name);
+		}
 	}
 
 	if ((error = device_pm_add(dev)))
@@ -458,8 +461,10 @@ void device_del(struct device * dev)
 		sysfs_remove_link(&dev->kobj, "subsystem");
 		sysfs_remove_link(&dev->class->subsys.kset.kobj, dev->bus_id);
 		class_name = make_class_name(dev->class->name, &dev->kobj);
-		sysfs_remove_link(&dev->kobj, "device");
-		sysfs_remove_link(&dev->parent->kobj, class_name);
+		if (parent) {
+			sysfs_remove_link(&dev->kobj, "device");
+			sysfs_remove_link(&dev->parent->kobj, class_name);
+		}
 		kfree(class_name);
 		down(&dev->class->sem);
 		list_del_init(&dev->node);
@@ -596,10 +601,6 @@ struct device *device_create(struct clas
 
 	if (class == NULL || IS_ERR(class))
 		goto error;
-	if (parent == NULL) {
-		printk(KERN_WARNING "%s does not work yet for NULL parents\n", __FUNCTION__);
-		goto error;
-	}
 
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 	if (!dev) {