Hello Greg,

>>>>+/* This is a mere directory in sysfs. No methods are needed. */
>>>>+static struct kobj_type bd_holder_ktype = {
>>>>+	.release	= NULL,
>>>>+	.sysfs_ops	= NULL,
>>>>+	.default_attrs	= NULL,
>>>>+};
>>>
>>>That doesn't look right.  You always need a release function.

I updated the patch based your comments.
Could you take a look at this version whether there's
any problematic use of sysfs/kobjects?

   - I removed embedded child-kobjects from struct block_device
     and struct gendisk which I added in my previous patch.
     Kobject registration occurs when gendisk or hd_struct is
     registered. Release function of the kobject type is added.
   - Reference counting of kobjects is done in much symmetric
     manner than before.
   - Added bd_claim_by_disk/bd_release_from_disk inline functions
     to help proper reference counting.

Thanks,
-- 
Jun'ichi Nomura, NEC Solutions (America), Inc.