On 3/22/21 3:29 AM, Eelco Chaudron wrote:
>
>
> On 20 Mar 2021, at 4:42, David Ahern wrote:
>
>> On 3/19/21 3:47 PM, Lorenzo Bianconi wrote:
>>> diff --git a/include/net/xdp.h b/include/net/xdp.h
>>> index 19cd6642e087..e47d9e8da547 100644
>>> --- a/include/net/xdp.h
>>> +++ b/include/net/xdp.h
>>> @@ -75,6 +75,10 @@ struct xdp_buff {
>>> struct xdp_txq_info *txq;
>>> u32 frame_sz:31; /* frame size to deduce data_hard_end/reserved
>>> tailroom*/
>>> u32 mb:1; /* xdp non-linear buffer */
>>> + u32 frame_length; /* Total frame length across all buffers. Only
>>> needs
>>> + * to be updated by helper functions, as it will be
>>> + * initialized at XDP program start.
>>> + */
>>> };
>>>
>>> static __always_inline void
>>
>> If you do another version of this set ...
>>
>> I think you only need 17-bits for the frame length (size is always <=
>> 128kB). It would be helpful for extensions to xdp if you annotated how
>> many bits are really needed here.
>
> Guess this can be done, but I did not too avoid the use of constants to
> do the BPF extraction.
> Here is an example of what might need to be added, as adding them before
> made people unhappy ;)
>
> https://elixir.bootlin.com/linux/v5.12-rc4/source/include/linux/skbuff.h#L801
>
>
I was just referring to a code comment that bits can be taken from
frame_length for extensions - just like the mb bit takes from frame_sz
(and it too has bits available since 2GB is way larger than actually
needed).
