HAMMER_HEAD_ALIGN_MASK
if ((head->hdr_size & HAMMER_HEAD_ALIGN_MASK) ||
if ((hdr->hdr_size & HAMMER_HEAD_ALIGN_MASK) ||
(((bytes) + HAMMER_HEAD_ALIGN_MASK) & ~HAMMER_HEAD_ALIGN_MASK)
(head->hdr_size & HAMMER_HEAD_ALIGN_MASK)) {