for_each_sg_dma_page
for_each_sg_dma_page(list, &dma_iter, sglen, 0) {
for_each_sg_dma_page(list, &dma_iter, length, 0)
for_each_sg_dma_page(sg->sgl, &sg_iter, sg->nents, 0) {
for_each_sg_dma_page((sgt)->sgl, dma_iter, (sgt)->nents, pgoffset)