BD_LOCKPTR
#define BD_LOCK(bd) mtx_lock(BD_LOCKPTR((bd)))
#define BD_UNLOCK(bd) mtx_unlock(BD_LOCKPTR((bd)))
#define BD_ASSERT_LOCKED(bd) mtx_assert(BD_LOCKPTR((bd)), MA_OWNED)
KASSERT(BQ_LOCKPTR(bq) == BD_LOCKPTR(bd),
error = msleep(&bd->bd_wanted, BD_LOCKPTR(bd),
msleep(&bd->bd_wanted, BD_LOCKPTR(bd),