kobject: Add support for default attribute groups to kobj_type

kobj_type currently uses a list of individual attributes to store
default attributes. Attribute groups are more flexible than a list of
attributes because groups provide support for attribute visibility. So,
add support for default attribute groups to kobj_type.

In future patches, the existing uses of kobj_type’s attribute list will
be converted to attribute groups. When that is complete, kobj_type’s
attribute list, “default_attrs”, will be removed.

Signed-off-by: Kimberly Brown <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/kobject.h

···
 struct kobj_type {
 	void (*release)(struct kobject *kobj);
 	const struct sysfs_ops *sysfs_ops;
-	struct attribute **default_attrs;
+	struct attribute **default_attrs;	/* use default_groups instead */
+	const struct attribute_group **default_groups;
 	const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj);
 	const void *(*namespace)(struct kobject *kobj);
 	void (*get_ownership)(struct kobject *kobj, kuid_t *uid, kgid_t *gid);

lib/kobject.c

···
 
 static int create_dir(struct kobject *kobj)
 {
+	const struct kobj_type *ktype = get_ktype(kobj);
 	const struct kobj_ns_type_operations *ops;
 	int error;
 
···
 	if (error) {
 		sysfs_remove_dir(kobj);
 		return error;
+	}
+
+	if (ktype) {
+		error = sysfs_create_groups(kobj, ktype->default_groups);
+		if (error) {
+			sysfs_remove_dir(kobj);
+			return error;
+		}
 	}
 
 	/*
···
 void kobject_del(struct kobject *kobj)
 {
 	struct kernfs_node *sd;
+	const struct kobj_type *ktype = get_ktype(kobj);
 
 	if (!kobj)
 		return;
 
 	sd = kobj->sd;
+
+	if (ktype)
+		sysfs_remove_groups(kobj, ktype->default_groups);
+
 	sysfs_remove_dir(kobj);
 	sysfs_put(sd);