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

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Message-ID: <2508ea8d-b7e3-49dc-b110-7eba1e4ece4d@kernel.org>
Date: Thu, 8 May 2025 17:04:25 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Jon Kohler <jon@...anix.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 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>,
 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()

On 08/05/2025 16.24, Jon Kohler wrote:
> 
>> On May 8, 2025, at 10:16 AM, Jesper Dangaard Brouer <hawk@...nel.org> wrote:
>>
[...]
>>
>> AFAICR there is also some dual packet handling code path for XDP in
>> vhost_net/tun.  I'm also willing to take the paper-cut, for cleaning
>> that up.
>>
>> --Jesper
> 
> When you say dual packet handling, what are you referring to specifically?

The important part of the sentence was *code path*, as in multiple code 
path for packets.

You tricked me into looking up the code for you...

It was in drivers/net/virtio_net.c where function receive_buf() calls[1]
three different functions based on different checks.  Some cases support
XDP and others don't.  I though you talked about this in another thread?

--Jesper

[1] 
https://elixir.bootlin.com/linux/v6.15-rc5/source/drivers/net/virtio_net.c#L2570-L2573