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Date:   Tue, 3 Jan 2023 17:21:53 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= <toke@redhat.com>
Cc:     Tariq Toukan <ttoukan.linux@gmail.com>,
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        ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net,
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        Jesper Dangaard Brouer <brouer@redhat.com>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Andy Gospodarek <gospo@broadcom.com>,
        Lorenzo Bianconi <lorenzo@kernel.org>, gal@nvidia.com,
        Saeed Mahameed <saeedm@nvidia.com>, tariqt@nvidia.com
Subject: Re: [PATCH net-next v2] samples/bpf: fixup some tools to be able to
 support xdp multibuffer
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On Tue, 03 Jan 2023 16:19:49 +0100 Toke H=C3=B8iland-J=C3=B8rgensen 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=20
so the linear part would have no data, just headers.

A random datapoint is that bpf_xdp_adjust_head() seems=20
to enforce that there is at least ETH_HLEN.