From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6A806C43461 for ; Mon, 14 Sep 2020 05:26:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2014F21655 for ; Mon, 14 Sep 2020 05:26:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=piap.pl header.i=@piap.pl header.b="Di22R3LD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726092AbgINF0W (ORCPT ); Mon, 14 Sep 2020 01:26:22 -0400 Received: from ni.piap.pl ([195.187.100.5]:38692 "EHLO ni.piap.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726027AbgINF0T (ORCPT ); Mon, 14 Sep 2020 01:26:19 -0400 Received: from t19.piap.pl (OSB1819.piap.pl [10.0.9.19]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ni.piap.pl (Postfix) with ESMTPSA id 77894443565; Mon, 14 Sep 2020 07:26:12 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 ni.piap.pl 77894443565 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=piap.pl; s=mail; t=1600061173; bh=b36UtK65i/l+Kip5dYP2VFfv1iztlojBnFJGyz/GjAw=; h=From:To:Cc:Subject:References:Date:In-Reply-To:From; b=Di22R3LDlfbvvRM14LvwQ60tBgCi+6aHC2m/aMRXjoYKX8lqTy70Kg61mDLX5Gg+G jSSPi0X4GxPgHeHWKaMvfwvZLps/7dN27hp+vbDX4TliQrYN1CL/ROkAKdS7avZERR hH2u55sL7H/+eboAzYBgHGr+x4fBD5SgYFSKhpVU= From: =?utf-8?Q?Krzysztof_Ha=C5=82asa?= To: Xie He Cc: Jakub Kicinski , Krzysztof Halasa , "David S. Miller" , Linux Kernel Network Developers , LKML , Martin Schiller , Willem de Bruijn Subject: Re: [PATCH net v2] drivers/net/wan/hdlc_fr: Add needed_headroom for PVC devices References: <20200903000658.89944-1-xie.he.0141@gmail.com> <20200904151441.27c97d80@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Date: Mon, 14 Sep 2020 07:26:12 +0200 In-Reply-To: (Xie He's message of "Fri, 4 Sep 2020 18:28:38 -0700") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-KLMS-Rule-ID: 4 X-KLMS-Message-Action: skipped X-KLMS-AntiSpam-Status: not scanned, whitelist X-KLMS-AntiPhishing: not scanned, whitelist X-KLMS-AntiVirus: Kaspersky Security for Linux Mail Server, version 8.0.3.30, not scanned, whitelist Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Xie He writes: > The HDLC device is not actually prepending any header when it is used > with this driver. When the PVC device has prepended its header and > handed over the skb to the HDLC device, the HDLC device just hands it > over to the hardware driver for transmission without prepending any > header. That's correct. IIRC: - Cisco and PPP modes add 4 bytes - Frame Relay adds 4 (specific protocols - mostly IPv4) or 10 (general case) bytes. There is that pvcX->hdlcX transition which adds nothing (the header is already in place when the packet leaves pvcX device). - Raw mode adds nothing (IPv4 only, though it could be modified for both IPv4/v6 easily) - Ethernet (hdlc_raw_eth.c) adds normal Ethernet header. (I had been "unplugged" for some time). --=20 Krzysztof Halasa Sie=C4=87 Badawcza =C5=81ukasiewicz Przemys=C5=82owy Instytut Automatyki i Pomiar=C3=B3w PIAP Al. Jerozolimskie 202, 02-486 Warszawa