netdev - Re: [PATCH net-next v2] samples/bpf: fixup some tools to be able to support xdp multibuffer

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Date:   Wed, 4 Jan 2023 17:17:33 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
        hawk@...nel.org, john.fastabend@...il.com, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, lorenzo.bianconi@...hat.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Andy Gospodarek <gospo@...adcom.com>, gal@...dia.com,
        Saeed Mahameed <saeedm@...dia.com>, tariqt@...dia.com
Subject: Re: [PATCH net-next v2] samples/bpf: fixup some tools to be able to
 support xdp multibuffer

On Wed, 04 Jan 2023 13:28:57 +0100 Toke Høiland-Jørgensen wrote:
> >> Interesting! :) My mental model was closer to GRO by frags 
> >> so the linear part would have no data, just headers.  
> >
> > That is assumption as well.  
> 
> Right, okay, so how many headers? Only Ethernet, or all the way up to
> L4 (TCP/UDP)?

If we're speaking about guarantees or hard requirements - I think that
we can only require / guarantee the Ethernet header. Requiring more
will be defeated by tunnels (i.e. adjust_head() + redirect to a veth).

> I do seem to recall a discussion around the header/data split for TCP
> specifically, but I think I mentally put that down as "something people
> may way to do at some point in the future", which is why it hasn't made
> it into my own mental model (yet?) :)