Re: [PATCH bpf-next 2/4] bpf: Craft non-linear skbs in BPF_PROG_TEST_RUN

[Amery Hung <ameryhung@gmail.com>]

On 9/4/25 9:02 AM, Daniel Borkmann wrote:
> On 9/4/25 5:56 PM, Alexei Starovoitov wrote:
>> On Thu, Sep 4, 2025 at 5:11 AM Paul Chaignon 
>> <paul.chaignon@gmail.com> wrote:
>>>
>>> This patch adds support for crafting non-linear skbs in BPF test runs
>>> for tc programs, via a new flag BPF_F_TEST_SKB_NON_LINEAR. When this
>>> flag is set, only the L2 header is pulled in the linear area.
>>
>> ...
>>
>>> +               /* eth_type_trans expects the Ethernet header in the 
>>> linear area. */
>>> +               __pskb_pull_tail(skb, ETH_HLEN);
>>
>> Looks useful, but only L2 ? Is it realistic ?
>> I don't recall any driver that would do L2 only.
>> Is L2 only enough to cover all corner cases in your progs ?
>> Should the linear size be a configurable parameter for prog_run() ?
>
> Yeah perhaps we could make this configurable. The ETH_HLEN is a common 
> case
> we've seen and also what virtual drivers pull in at min, but with NICs 
> doing
> header/data split its probably better to let the user define this as part
> of the testing. Then we're more flexible.
>

How about letting users specify the linear size through ctx->data_end? I 
am working on a set that introduces a kfunc, bpf_xdp_pull_data(). A part 
of is to support non-linear xdp_buff in test_run_xdp, and I am doing it 
through ctx->data_end. Is it something reasonable for test_run_skb?

> Cheers,
> Daniel