清单 1. 直接访问内存

static int dmabuf_mmap(...)
{
  size >>= PAGE_SHIFT;
  for (nr = 0; nr < size; nr++)
     if (!db->sgbuf[nr])
            return -EINVAL;
  db->mapped = 1;
  for (nr = 0; nr < size; nr++) {
     if (remap_page_range (start,
                           virt_to_phys(db->sgbuf[nr]),
                           PAGE_SIZE, prot))
           return -EAGAIN;
     start += PAGE_SIZE;
  }
  return 0;
}