MD_UNIT
sc = device_lookup_private(&md_cd, MD_UNIT(dev));
unit = MD_UNIT(dev);
sc = device_lookup_private(&md_cd, MD_UNIT(dev));
sc = device_lookup_private(&md_cd, MD_UNIT(dev));
sc = device_lookup_private(&md_cd, MD_UNIT(dev));
sc = device_lookup_private(&md_cd, MD_UNIT(bp->b_dev));
if ((sc = device_lookup_private(&md_cd, MD_UNIT(dev))) == NULL)