dax_iomap_direct_access
ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
ret = dax_iomap_direct_access(iomap, copy_pos, copy_len, &daddr, NULL);
ret = dax_iomap_direct_access(srcmap, copy_pos, copy_len, &saddr, NULL);
err = dax_iomap_direct_access(iomap, pos, size, &kaddr, &pfn);
ret = dax_iomap_direct_access(smap, pos1, ALIGN(pos1 + len, PAGE_SIZE),
ret = dax_iomap_direct_access(dmap, pos2, ALIGN(pos2 + len, PAGE_SIZE),