ceph_fscrypt_page_offset
offset = ceph_fscrypt_page_offset(ceph_wbc->pages[0]);
BUG_ON(len < ceph_fscrypt_page_offset(page) + thp_size(page) - offset);
if (end > ceph_fscrypt_page_offset(page) + thp_size(page))
end = ceph_fscrypt_page_offset(page) + thp_size(page);