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

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Message-ID: <87bkne32ly.fsf@toke.dk>
Date:   Wed, 04 Jan 2023 13:28:57 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     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

Lorenzo Bianconi <lorenzo@...nel.org> writes:

>> On Tue, 03 Jan 2023 16:19:49 +0100 Toke Høiland-Jørgensen wrote:
>> > Hmm, good question! I don't think we've ever explicitly documented any
>> > assumptions one way or the other. My own mental model has certainly
>> > always assumed the first frag would continue to be the same size as in
>> > non-multi-buf packets.
>> 
>> 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)?

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?) :)

-Toke