netdev - Re: [PATCH 00/11] XDP unaligned chunk placement support

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Message-ID: <20190627142534.4f4b8995@cakuba.netronome.com>
Date:   Thu, 27 Jun 2019 14:25:34 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     "Laatz, Kevin" <kevin.laatz@...el.com>
Cc:     Jonathan Lemon <jonathan.lemon@...il.com>, netdev@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net, bjorn.topel@...el.com,
        magnus.karlsson@...el.com, bpf@...r.kernel.com,
        intel-wired-lan@...ts.osuosl.org, bruce.richardson@...el.com,
        ciara.loftus@...el.com
Subject: Re: [PATCH 00/11] XDP unaligned chunk placement support

On Thu, 27 Jun 2019 12:14:50 +0100, Laatz, Kevin wrote:
> On the application side (xdpsock), we don't have to worry about the user 
> defined headroom, since it is 0, so we only need to account for the 
> XDP_PACKET_HEADROOM when computing the original address (in the default 
> scenario).

That assumes specific layout for the data inside the buffer.  Some NICs
will prepend information like timestamp to the packet, meaning the
packet would start at offset XDP_PACKET_HEADROOM + metadata len..

I think that's very limiting.  What is the challenge in providing
aligned addresses, exactly?