HAMMER_ZONE_LAYER2_NEXT_OFFSET
HAMMER_ZONE_LAYER2_NEXT_OFFSET(blockmap->next_offset);
off = HAMMER_ZONE_LAYER2_NEXT_OFFSET(off);
off = HAMMER_ZONE_LAYER2_NEXT_OFFSET(off);
next_offset = HAMMER_ZONE_LAYER2_NEXT_OFFSET(next_offset);
next_offset = HAMMER_ZONE_LAYER2_NEXT_OFFSET(next_offset);