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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8278dbd0732sm465119085a.48.2025.09.15.10.20.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Sep 2025 10:20:09 -0700 (PDT) Date: Mon, 15 Sep 2025 10:20:05 -0700 From: Stephen Hemminger To: Daniel Borkmann Cc: Alasdair McWilliam , netdev@vger.kernel.org, Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Subject: Re: [PATCH] rtnetlink: add needed_{head,tail}room attributes Message-ID: <20250915102005.2ddf29d7@hermes.local> In-Reply-To: References: <20250915163217.368435-1-alasdair@mcwilliam.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 15 Sep 2025 18:49:55 +0200 Daniel Borkmann 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 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.