Re: [PATCH net-next v3] xdp: Add helpers for head length, headroom, and metadata length

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 07/05/2025 19.47, Jon Kohler wrote:
> 
> 
>> On May 7, 2025, at 1:21 PM, Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:
>>
>>
>> Jesper Dangaard Brouer wrote:
>>>
>>>
>>> On 07/05/2025 19.02, Zvi Effron wrote:
>>>> On Wed, May 7, 2025 at 9:37 AM Jesper Dangaard Brouer <hawk@kernel.org> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 07/05/2025 15.29, Willem de Bruijn wrote:
>>>>>> Stanislav Fomichev wrote:
>>>>>>> On 05/06, Jon Kohler wrote:
>>>>>>>> Introduce new XDP helpers:
>>>>>>>> - xdp_headlen: Similar to skb_headlen
>>>>>
>>>>> I really dislike xdp_headlen(). This "headlen" originates from an SKB
>>>>> implementation detail, that I don't think we should carry over into XDP
>>>>> land.
>>>>> We need to come up with something that isn't easily mis-read as the
>>>>> header-length.
>>>>
>>>> ... snip ...
>>>>
>>>>>>> + * xdp_headlen - Calculate the length of the data in an XDP buffer
>>>>
>>>> How about xdp_datalen()?
>>>
>>> Yes, I like xdp_datalen() :-)
>>
>> This is confusing in that it is the inverse of skb->data_len:
>> which is exactly the part of the data not in the skb head.
>>
>> There is value in consistent naming. I've never confused headlen
>> with header len.
>>
>> But if diverging, at least let's choose something not
>> associated with skbs with a different meaning.
> 
> Brainstorming a few options:
> - xdp_head_datalen() ?
> - xdp_base_datalen() ?
> - xdp_base_headlen() ?
> - xdp_buff_datalen() ?
> - xdp_buff_headlen() ?
> - xdp_datalen() ? (ZivE, JesperB)
> - xdp_headlen() ? (WillemB, JonK, StanislavF, JacobK, DanielB)
> 

What about keeping it really simple: xdp_buff_len() ?

Or even simpler: xdp_len() as the function documentation already
describe this doesn't include frags.

To Jon, you seems to be on a cleanup spree:
For SKBs netstack have this diagram documented [1].  Which also explains
the concept of a "head" buffer, which isn't a concept for XDP.  I would
really like to see a diagram documenting both xdp_buff and xdp_frame
data structures via ascii art, like the one for SKBs. (Hint, this is
actually defined in the header file include/linux/skbuff.h, but
converted to RST/HTML format.)

[1] https://docs.kernel.org/networking/skbuff.html

--Jesper