null_get_extents (struct rw *rw, uintptr_t index,
                  uint64_t offset, uint64_t count,
                  extent_list *ret)
{
  abort ();
}
null_get_extents (struct rw *rw, uintptr_t index,
                  uint64_t offset, uint64_t count,
                  extent_list *ret)
{
  abort ();
}