HAMMER_HEAD_SIGNATURE
head->hdr_signature = HAMMER_HEAD_SIGNATURE;
if (head->hdr_signature != HAMMER_HEAD_SIGNATURE) {
redo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
redo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
redo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
undo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
undo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
undo->head.hdr_signature = HAMMER_HEAD_SIGNATURE;
head->hdr_signature = HAMMER_HEAD_SIGNATURE;
head->hdr_signature = HAMMER_HEAD_SIGNATURE;