Re: [Intel-wired-lan] [PATCH bpf-next v5 8/8] selftests: net: add test for XDP_PASS skb checksum invalidation

On Wed, 22 Jul 2026 11:00:07 -0700 Stanislav Fomichev wrote:
> > > This is about current drivers that only report UNNECESSARY with xdp: the xdp
> > > prog has to maintain in-packet checksum if it changes the payload. I think
> > > it's a fair assumption?  
> > 
> > What about decap? If we decap the header that device validated 
> > as UNNECESSARY there's no possibility of maintaining the checksum
> > (by which IIUC you mean correcting it in along the payload changes).
> > 
> > I think we'd need some API to "decrement the csum level" ?
> > Or some heuristic in the drivers to decrement if the head moved
> > by at least len(IP+UDP) into the packet ?  
> 
> True :-/ I guess one more case to document?

What would we be documenting? That it's a known bug and we have no idea
how to address it? Or am I missing something?

Again: 
 .. the ask was to sketch out the plan of explicitly
 updating/invalidating the checksum even if we don't 
 implement it today