legacy_device
struct legacy_device *atdev = DEVTOAT(child);
struct legacy_device *atdev;
atdev = kmalloc(sizeof(struct legacy_device), M_LEGACYDEV,
struct legacy_device *atdev = DEVTOAT(child);
struct legacy_device *atdev = DEVTOAT(child);
#define DEVTOAT(dev) ((struct legacy_device *)device_get_ivars(dev))