linux-kernel - Re: [PATCH net-next v2 3/3] tun: AF

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Date: Fri, 01 Mar 2024 13:40:46 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>, 
 Yunjian Wang <wangyunjian@...wei.com>
Cc: mst@...hat.com, 
 willemdebruijn.kernel@...il.com, 
 jasowang@...hat.com, 
 kuba@...nel.org, 
 bjorn@...nel.org, 
 magnus.karlsson@...el.com, 
 jonathan.lemon@...il.com, 
 davem@...emloft.net, 
 bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 kvm@...r.kernel.org, 
 virtualization@...ts.linux.dev, 
 xudingke@...wei.com, 
 liwei395@...wei.com
Subject: Re: [PATCH net-next v2 3/3] tun: AF_XDP Tx zero-copy support

Maciej Fijalkowski wrote:
> On Wed, Feb 28, 2024 at 07:05:56PM +0800, Yunjian Wang wrote:
> > This patch set allows TUN to support the AF_XDP Tx zero-copy feature,
> > which can significantly reduce CPU utilization for XDP programs.
> 
> Why no Rx ZC support though? What will happen if I try rxdrop xdpsock
> against tun with this patch? You clearly allow for that.

This is AF_XDP receive zerocopy, right?

The naming is always confusing with tun, but even though from a tun
PoV this happens on ndo_start_xmit, it is the AF_XDP equivalent to
tun_put_user.

So the implementation is more like other device's Rx ZC.

I would have preferred that name, but I think Jason asked for this
and given tun's weird status, there is something bo said for either.