MBLKL
#undef MBLKL
#define MBLKL(_mp_) ((uintptr_t)(_mp_)->b_wptr - (uintptr_t)(_mp_)->b_rptr)
#define MBLKL(_mp_) ((uintptr_t)(_mp_)->b_wptr - (uintptr_t)(_mp_)->b_rptr)
#define MBLKL(mp) ((uintptr_t)(mp)->b_wptr - (uintptr_t)(mp)->b_rptr)
#define MBLKL(mp) _PTRDIFF((mp)->b_wptr, (mp)->b_rptr)