netdev - Re: [xdp-hints] Re: [PATCH bpf-next 06/11] xdp: Carry over xdp metadata into skb context

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Message-ID: <87bkp7jklt.fsf@toke.dk>
Date:   Wed, 16 Nov 2022 10:48:30 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>,
        Stanislav Fomichev <sdf@...gle.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        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, bpf@...r.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next 06/11] xdp: Carry over xdp
 metadata into skb context

Martin KaFai Lau <martin.lau@...ux.dev> writes:

> On 11/14/22 7:02 PM, Stanislav Fomichev wrote:
>> Implement new bpf_xdp_metadata_export_to_skb kfunc which
>> prepares compatible xdp metadata for kernel consumption.
>> This kfunc should be called prior to bpf_redirect
>> or when XDP_PASS'ing the frame into the kernel (note, the drivers
>> have to be updated to enable consuming XDP_PASS'ed metadata).
>> 
>> veth driver is amended to consume this metadata when converting to skb.
>> 
>> Internally, XDP_FLAGS_HAS_SKB_METADATA flag is used to indicate
>> whether the frame has skb metadata. The metadata is currently
>> stored prior to xdp->data_meta. bpf_xdp_adjust_meta refuses
>> to work after a call to bpf_xdp_metadata_export_to_skb (can lift
>> this requirement later on if needed, we'd have to memmove
>> xdp_skb_metadata).
>
> It is ok to refuse bpf_xdp_adjust_meta() after bpf_xdp_metadata_export_to_skb() 
> for now.  However, it will also need to refuse bpf_xdp_adjust_head().

I'm also OK with deferring this, although I'm wondering if it isn't just
as easy to just add the memmove() straight away? :)

-Toke