Re: [RFC bpf-next v1 2/7] bpf: Allow bpf_xdp_shrink_data to shrink a frag from head and tail

[Amery Hung <ameryhung@xxxxxxxxx>]

On Thu, Aug 28, 2025 at 6:44 AM Nimrod Oren <noren@xxxxxxxxxx> wrote:
>
> On 25/08/2025 22:39, Amery Hung wrote:
> > Move skb_frag_t adjustment into bpf_xdp_shrink_data() and extend its
> > functionality to be able to shrink an xdp fragment from both head and
> > tail. In a later patch, bpf_xdp_pull_data() will reuse it to shrink an
> > xdp fragment from head.
> I had assumed that XDP multi-buffer frags must always be the same size,
> except for the last one. If that’s the case, shrinking from the head
> seems to break this rule.

I am not aware of the assumption in the code. Is this documented somewhere?

Thanks,
Amery