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

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Date:   Tue, 15 Nov 2022 10:37:51 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Toke Høiland-Jørgensen <toke@...hat.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] [PATCH bpf-next 00/11] xdp: hints via kfuncs

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

?

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