netdev - Re: [xdp-hints] Re: [PATCH bpf-next 00/11] xdp: hints via kfuncs

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Date:   Tue, 15 Nov 2022 23:31:17 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        haoluo@...gle.com, jolsa@...nel.org,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next 00/11] xdp: hints via kfuncs

Stanislav Fomichev <sdf@...gle.com> writes:

> On Tue, Nov 15, 2022 at 7:54 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Stanislav Fomichev <sdf@...gle.com> writes:
>>
>> > - drop __randomize_layout
>> >
>> >   Not sure it's possible to sanely expose it via UAPI. Because every
>> >   .o potentially gets its own randomized layout, test_progs
>> >   refuses to link.
>>
>> So this won't work if the struct is in a kernel-supplied UAPI header
>> (which would include the __randomize_layout tag). But if it's *not* in a
>> UAPI header it should still be included in a stable form (i.e., without
>> the randomize tag) in vmlinux.h, right? Which would be the point:
>> consumers would be forced to read it from there and do CO-RE on it...
>
> So you're suggesting something like the following in the uapi header?
>
> #ifndef __KERNEL__
> #define __randomize_layout
> #endif
>
> ?

I actually just meant "don't put struct xdp_metadata in an UAPI header
file at all". However, I can see how that complicates having the
skb_metadata pointer in struct xdp_md, so if the above works, that's
fine with me as well :)

> Let me try to add some padding arguments to xdp_skb_metadata plus the
> above to see how it goes.

Cool!

-Toke