在 2022/8/4 下午9:50, Cornelia Huck 写道:
> On Thu, Aug 04 2022, Heng Qi<hengqi@linux.alibaba.com>  wrote:
>
>> 在 2022/8/4 下午2:27, Jason Wang 写道:
>>> On Mon, Aug 1, 2022 at 2:59 PM Heng Qi<hengqi@linux.alibaba.com>   wrote:
>>>> @@ -3820,9 +3826,13 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>>>>    driver MUST NOT use the \field{csum_start} and \field{csum_offset}.
>>>>
>>>>    If one of the VIRTIO_NET_F_GUEST_TSO4, TSO6, UFO, USO4 or USO6 options have
>>>> -been negotiated, the driver MAY use \field{hdr_len} only as a hint about the
>>>> +been negotiated and the VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags}
>>>> +is not set, the driver MAY use \field{hdr_len} only as a hint about the
>>>>    transport header size.
>>>> -The driver MUST NOT rely on \field{hdr_len} to be correct.
>>>> +
>>>> +If the VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags} is not set, the driver
>>>> +MUST NOT rely on \field{hdr_len} to be correct.
>>> I think we should keep the above description as-is. For whatever case,
>>> the driver must not trust the metadata set by the device and must
>>> perform necessary sanity tests on them.
>>
>> My idea is to keep the current description as it is,
>> but to emphasize in the next version:
>> "If the VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags} is set,
>> the driver MAY treat the \field{hdr_len} as the length of the
>> protocol header inside the first descriptor."
>
> Just to be clear, you suggest using
>
> "If one of the VIRTIO_NET_F_GUEST_TSO4, TSO6, UFO, USO4 or USO6 options have
> been negotiated, the driver MAY use \field{hdr_len} only as a hint about the
> transport header size.
>
> The driver MUST NOT rely on \field{hdr_len} to be correct.
>
> If the VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags} is set,
> the driver MAY treat the \field{hdr_len} as the length of the
> protocol header inside the first descriptor."

Yes. I will use the above description to make it clearer in the next version.


>
> (Maybe "...the driver MAY use \field{hdr_len} as a hint about the length
> of the protocol header..."? It's still not reliable, right?)
>
\field{hdr_len} is unreliable when VIRTIO_NET_F_SPLIT_HEADER is not negotiated.


If VIRTIO_NET_F_SPLIT_HEADER is negotiated, "split header" MAY perform the split
from the IP layer, so the protocol header and the transport header are different.

so I think the "...the driver MAY use \field{hdr_len} only as a hint about the
transport header size..." paragraph can be left as-is.