driver core: fix namespace issue with devices assigned to classes

- uses a kset in "struct class" to keep track of all directories
    belonging to this class
  - merges with the /sys/devices/virtual logic.
  - removes the namespace-dir if the last member of that class
    leaves the directory.

There may be locking or refcounting fixes left, I stopped when it seemed
to work with network and sound modules. :)

From: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

lib/kobject_uevent.c

@@ -115,6 +115,16 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 			return 0;
 		}
 
+	/* originating subsystem */
+	if (uevent_ops && uevent_ops->name)
+		subsystem = uevent_ops->name(kset, kobj);
+	else
+		subsystem = kobject_name(&kset->kobj);
+	if (!subsystem) {
+		pr_debug("unset subsytem caused the event to drop!\n");
+		return 0;
+	}
+
 	/* environment index */
 	envp = kzalloc(NUM_ENVP * sizeof (char *), GFP_KERNEL);
 	if (!envp)
@@ -134,12 +144,6 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 		goto exit;
 	}
 
-	/* originating subsystem */
-	if (uevent_ops && uevent_ops->name)
-		subsystem = uevent_ops->name(kset, kobj);
-	else
-		subsystem = kobject_name(&kset->kobj);
-
 	/* event environemnt for helper process only */
 	envp[i++] = "HOME=/";
 	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";