netdev - Re: [PATCH] rtnetlink: add needed

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Message-ID: <20250915102005.2ddf29d7@hermes.local>
Date: Mon, 15 Sep 2025 10:20:05 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: Alasdair McWilliam <alasdair@...illiam.dev>, netdev@...r.kernel.org,
 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>
Subject: Re: [PATCH] rtnetlink: add needed_{head,tail}room attributes

On Mon, 15 Sep 2025 18:49:55 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:

> Hi Alasdair,
> 
> On 9/15/25 6:32 PM, Alasdair McWilliam wrote:
> > Various network interface types make use of needed_{head,tail}room values
> > to efficiently reserve buffer space for additional encapsulation headers,
> > such as VXLAN, Geneve, IPSec, etc. However, it is not currently possible
> > to query these values in a generic way.
> > 
> > Introduce ability to query the needed_{head,tail}room values of a network
> > device via rtnetlink, such that applications that may wish to use these
> > values can do so.
> > 
> > Signed-off-by: Alasdair McWilliam <alasdair@...illiam.dev>

Why is this info needed in user space?
How would an application use this?
Seems like a hardware specific optimization that should be hidden in driver.