nvme_tryget_ns_head
if (nvme_tryget_ns_head(h))
if (!nvme_tryget_ns_head(disk->private_data))
if (!nvme_tryget_ns_head(cdev_to_ns_head(inode->i_cdev)))
nvme_tryget_ns_head(head);
bool nvme_tryget_ns_head(struct nvme_ns_head *head);