BQ_LOCKPTR
#define BQ_LOCK(bq) mtx_lock(BQ_LOCKPTR((bq)))
#define BQ_UNLOCK(bq) mtx_unlock(BQ_LOCKPTR((bq)))
#define BQ_ASSERT_LOCKED(bq) mtx_assert(BQ_LOCKPTR((bq)), MA_OWNED)
KASSERT(BQ_LOCKPTR(bq) == BD_LOCKPTR(bd),