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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 50691C10F0E for ; Mon, 15 Apr 2019 10:41:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A6822064A for ; Mon, 15 Apr 2019 10:41:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727218AbfDOKlz (ORCPT ); Mon, 15 Apr 2019 06:41:55 -0400 Received: from s3.sipsolutions.net ([144.76.43.62]:36236 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726313AbfDOKly (ORCPT ); Mon, 15 Apr 2019 06:41:54 -0400 Received: by sipsolutions.net with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1hFz3Y-00058y-NI; Mon, 15 Apr 2019 12:41:44 +0200 Message-ID: Subject: Re: gsmtap design/extensions? From: Johannes Berg To: =?ISO-8859-1?Q?Bj=F8rn?= Mork Cc: Marcel Holtmann , Vadim Yanitskiy , Harald Welte , OpenBSC Mailing List , Sean Tranchetti , radiotap@netbsd.org, Dan Williams , netdev , "open list:NFC SUBSYSTEM" , Aleksander Morgado , Subash Abhinov Kasiviswanathan Date: Mon, 15 Apr 2019 12:41:42 +0200 In-Reply-To: <87d0ln1s0a.fsf@miraculix.mork.no> References: <46474c61d7748042cc0a1f23773186786020638e.camel@sipsolutions.net> <6F1998DC-EFD2-4145-BD81-A80F9DC7ED2D@holtmann.org> <1d64c578cd5b254d301cf1cac82f32a062916888.camel@sipsolutions.net> <92e8e142b6d441c1c995abc57d64ad7b7747a688.camel@sipsolutions.net> <87d0ln1s0a.fsf@miraculix.mork.no> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-2.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Mon, 2019-04-15 at 12:29 +0200, Bjørn Mork wrote: > > I don't understand where you are going here? Neither QMI, AT command nor > MBIM management are transported over netdevs. AT is usually transported > using simple USB bulk streams, exported to userspace as tty devices by > some USB serial driver. Both QMI and MBIM management are transported as > USB control messages, and exported to userspace as chardevs. There are > no netdevs involved. OK. I've also been looking at a driver for Intel modems, and I think it works that way. > > and people do things like "socat" to set up > > PTYs and pretend to have serial channels there, on top of the netdevs? > > I assume you are referring to my MBIM DSS examples here. I was more thinking of what I've been told the Intel modem does, actually. But that in turn might very well be inspired by what you documented there. I think the folks doing this were just trying to make it work and nobody really understands the whole landscape. > I don't know > if anyone is actually using that, so you should probably ignore it... > I'll happily admit it was a bad idea. Should have just added the > necessary code to map DSS channels to some sort of character device in > the driver, like most users requested. OK. So I guess a framework should consider that possibility, and let you create new chardevs for a given (DSS) channel? > But there really isn't anything in the MBIM spec saying how DSS should > be used. DSS is a generic data stream. Could easily be connected to a > single TCP session for example, in which case you'd probably want to > connect it to a TCP session in the other end too. So I wouldn't want to > force DSS into character devices on the host end. Fair point. I suppose some of these may also be debug channels that give you modem debug information, which is useful (if you can interpret it). > This doesn't rule out > a userspace controlled optional mapping though. We could probably still > add that, replacing the VLAN mapping with a chardev for a specific DSS > session if requested by userspace. I guess this is something to > consider for a generic cellular framework - supporting non-ip data > streams between modem and host. Right. > Adding to my previous excuses: The DSS implementation in the cdc_mbim > driver was added without having seen a single modem firmware with *any* > type of DSS support. It was purely based on spec{ification,culation}. > The VLAN mapping, along with examples of how to use socat to further map > the streams from VLANs into suitable application specific forms, seemed > like a simple and flexible enough solution. :-) johannes