driver core: class: Check namespace relevant parameters in class_register()

Device class has two namespace relevant fields which are usually
associated by the following usage:

struct class {
	...
	const struct kobj_ns_type_operations *ns_type;
	const void *(*namespace)(const struct device *dev);
	...
}
if (dev->class && dev->class->ns_type)
	dev->class->namespace(dev);

(1) The usage looks weird since it checks @ns_type but calls namespace()
(2) The usage implies both fields have dependency but their dependency
    is not currently enforced yet.

It is found for all existing class definitions that the other filed is
also assigned once one is assigned in current kernel tree.

Fixed by enforcing above existing dependency that both fields are required
for a device class to support namespace via parameter checks.
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://lore.kernel.org/r/20240822-class_fix-v1-1-2a6d38ba913a@quicinc.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/class.c

@@ -183,6 +183,17 @@ int class_register(const struct class *cls)
 
 	pr_debug("device class '%s': registering\n", cls->name);
 
+	if (cls->ns_type && !cls->namespace) {
+		pr_err("%s: class '%s' does not have namespace\n",
+		       __func__, cls->name);
+		return -EINVAL;
+	}
+	if (!cls->ns_type && cls->namespace) {
+		pr_err("%s: class '%s' does not have ns_type\n",
+		       __func__, cls->name);
+		return -EINVAL;
+	}
+
 	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
 	if (!cp)
 		return -ENOMEM;

drivers/base/core.c

@@ -2584,7 +2584,7 @@ static const void *device_namespace(const struct kobject *kobj)
 	const struct device *dev = kobj_to_dev(kobj);
 	const void *ns = NULL;
 
-	if (dev->class && dev->class->ns_type)
+	if (dev->class && dev->class->namespace)
 		ns = dev->class->namespace(dev);
 
 	return ns;