__sgt_iter
iter = __sgt_iter(pages->sgl, true);
.sgt = __sgt_iter(sgl, use_dma(iobase)),
r.sgt = __sgt_iter(__sg_next(r.sgt.sgp), use_dma(iobase));
r->sgt = __sgt_iter(__sg_next(r->sgt.sgp), use_dma(r->iobase));
(__iter) = __sgt_iter(__sg_next((__iter).sgp), true), 0 : 0)
for ((__iter) = __sgt_iter((__sgt)->sgl, false); \
(__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0 : 0)
for ((__iter) = __sgt_iter((__sgt)->sgl, true); \
(__iter) = __sgt_iter(__sg_next((__iter).sgp), true), 0 : 0)