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=-3.8 required=3.0 tests=BAYES_00, 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 84FCFC433DB for ; Mon, 1 Feb 2021 09:20:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 353D064E43 for ; Mon, 1 Feb 2021 09:20:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232828AbhBAJU3 (ORCPT ); Mon, 1 Feb 2021 04:20:29 -0500 Received: from mxout70.expurgate.net ([194.37.255.70]:60653 "EHLO mxout70.expurgate.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232758AbhBAJUT (ORCPT ); Mon, 1 Feb 2021 04:20:19 -0500 Received: from [127.0.0.1] (helo=localhost) by relay.expurgate.net with smtp (Exim 4.90) (envelope-from ) id 1l6VLl-0004xN-M0; Mon, 01 Feb 2021 10:18:25 +0100 Received: from [195.243.126.94] (helo=securemail.tdt.de) by relay.expurgate.net with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90) (envelope-from ) id 1l6VLk-0002MG-Ia; Mon, 01 Feb 2021 10:18:24 +0100 Received: from securemail.tdt.de (localhost [127.0.0.1]) by securemail.tdt.de (Postfix) with ESMTP id 2426C240041; Mon, 1 Feb 2021 10:18:24 +0100 (CET) Received: from mail.dev.tdt.de (unknown [10.2.4.42]) by securemail.tdt.de (Postfix) with ESMTP id 97CDE240040; Mon, 1 Feb 2021 10:18:23 +0100 (CET) Received: from mail.dev.tdt.de (localhost [IPv6:::1]) by mail.dev.tdt.de (Postfix) with ESMTP id 264DB200AA; Mon, 1 Feb 2021 10:18:23 +0100 (CET) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 01 Feb 2021 10:18:23 +0100 From: Martin Schiller To: Xie He Cc: Jakub Kicinski , "David S. Miller" , Linux X25 , Linux Kernel Network Developers , LKML , Krzysztof Halasa Subject: Re: [PATCH net] net: hdlc_x25: Use qdisc to queue outgoing LAPB frames Organization: TDT AG In-Reply-To: References: <20210127090747.364951-1-xie.he.0141@gmail.com> <20210128114659.2d81a85f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <3f67b285671aaa4b7903733455a730e1@dev.tdt.de> <20210129173650.7c0b7cda@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210130111618.335b6945@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Message-ID: <36a6c0769c57cd6835d32cc0fb95bca6@dev.tdt.de> X-Sender: ms@dev.tdt.de User-Agent: Roundcube Webmail/1.3.16 X-purgate-ID: 151534::1612171105-0000A9C4-B60B7990/0/0 X-purgate-type: clean X-purgate: clean Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-31 04:16, Xie He wrote: > On Sat, Jan 30, 2021 at 11:16 AM Jakub Kicinski > wrote: >> >> Sounds like too much afford for a sub-optimal workaround. >> The qdisc semantics are borken in the proposed scheme (double >> counting packets) - both in term of statistics and if user decides >> to add a policer, filter etc. > > Hmm... > > Another solution might be creating another virtual device on top of > the HDLC device (similar to what "hdlc_fr.c" does), so that we can > first queue L3 packets in the virtual device's qdisc queue, and then > queue the L2 frames in the actual HDLC device's qdisc queue. This way > we can avoid the same outgoing data being queued to qdisc twice. But > this would significantly change the way the user uses the hdlc_x25 > driver. > >> Another worry is that something may just inject a packet with >> skb->protocol == ETH_P_HDLC but unexpected structure (IDK if >> that's a real concern). > > This might not be a problem. Ethernet devices also allow the user to > inject raw frames with user constructed headers. "hdlc_fr.c" also > allows the user to bypass the virtual circuit interfaces and inject > raw frames directly on the HDLC interface. I think the receiving side > should be able to recognize and drop invalid frames. > >> It may be better to teach LAPB to stop / start the internal queue. >> The lower level drivers just needs to call LAPB instead of making >> the start/wake calls directly to the stack, and LAPB can call the >> stack. Would that not work? > > I think this is a good solution. But this requires changing a lot of > code. The HDLC subsystem needs to be changed to allow HDLC Hardware > Drivers to ask HDLC Protocol Drivers (like hdlc_x25.c) to stop/wake > the TX queue. The hdlc_x25.c driver can then ask the LAPB module to > stop/wake the queue. > > So this means new APIs need to be added to both the HDLC subsystem and > the LAPB module, and a number of HDLC Hardware Drivers need to be > changed to call the new API of the HDLC subsystem. > > Martin, do you have any suggestions? I have thought about this issue again. I also have to say that I have never noticed any problems in this area before. So again for (my) understanding: When a hardware driver calls netif_stop_queue, the frames sent from layer 3 (X.25) with dev_queue_xmit are queued and not passed "directly" to x25_xmit of the hdlc_x25 driver. So nothing is added to the write_queue anymore (except possibly un-acked-frames by lapb_requeue_frames). Shouldn't it actually be sufficient to check for netif_queue_stopped in lapb_kick and then do "nothing" if necessary? As soon as the hardware driver calls netif_wake_queue, the whole thing should just continue running. Or am I missing something?