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

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Message-ID: <475cc762-5183-90c8-a347-cc1dfa5c1976@linux.dev>
Date:   Wed, 16 Nov 2022 13:49:58 -0800
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Stanislav Fomichev <sdf@...gle.com>, bpf@...r.kernel.org,
        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>,
        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: [PATCH bpf-next 06/11] xdp: Carry over xdp metadata into skb
 context

On 11/16/22 1:12 PM, Jakub Kicinski wrote:
> On Mon, 14 Nov 2022 19:02:05 -0800 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).
> 
> IMO we should split the xdp -> skb work from the pure HW data access
> in XDP. We have a proof point here that there is a way of building
> on top of the first 5 patches to achieve the objective, and that's
> sufficient to let the prior work going in.

+1

Good idea.