linux-kernel - Re: [PATCH net-next] tun: use xdp_get_frame

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Message-ID: <681cb1d4cb20_2574d529466@willemb.c.googlers.com.notmuch>
Date: Thu, 08 May 2025 09:29:56 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jon Kohler <jon@...anix.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Jason Wang <jasowang@...hat.com>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 Jesper Dangaard Brouer <hawk@...nel.org>, 
 John Fastabend <john.fastabend@...il.com>, 
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next] tun: use xdp_get_frame_len()

Jon Kohler wrote:
> 
> 
> > On May 7, 2025, at 4:56 PM, Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
> > 
> > !-------------------------------------------------------------------|
> >  CAUTION: External Email
> > 
> > |-------------------------------------------------------------------!
> > 
> > Jon Kohler wrote:
> >> Use xdp_get_frame_len helper to ensure xdp frame size is calculated
> >> correctly in both single buffer and multi buffer configurations.
> > 
> > Not necessarily opposed, but multi buffer is not actually possible
> > in this code path, right?
> > 
> > tun_put_user_xdp only copies xdp_frame->data, for one.
> > 
> > Else this would also be fix, not net-next material.
> 
> Correct, this is a prep patch for future multi buffer support,
> I’m not aware of any path that can currently do that thru
> this code.
> 
> The reason for pursuing multi-buffer is to allow vhost/net
> batching to work again for large payloads.

I was not aware of that context. I'd add a comment to that in the
commit message, and send it as part of that series.