IOPIND
#define IOB_LCK(iop) (STDIOP(iop) ? &_xftab[IOPIND(iop)]._lock \
return (&_xftab[IOPIND(iop)]);
&x##fp->xlock : &_xftab[IOPIND(fp)]._lock
&x##fp->xstate : &_xftab[IOPIND(fp)]._state
altfd = _xftab[IOPIND(iop)]._altfd;