From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: gsmtap design/extensions? Date: Mon, 15 Apr 2019 12:41:42 +0200 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <87d0ln1s0a.fsf-3F4PFWf5pNjpjLOzFPqGjWGXanvQGlWp@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Unsubscribe: To: =?ISO-8859-1?Q?Bj=F8rn?= Mork Cc: Marcel Holtmann , Vadim Yanitskiy , Harald Welte , OpenBSC Mailing List , Sean Tranchetti , radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org, Dan Williams , netdev , "open list:NFC SUBSYSTEM" , Aleksander Morgado , Subash Abhinov Kasiviswanathan List-Id: radiotap@radiotap.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