From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schiller Subject: Re: [PATCH net-next RFC v4] net: hdlc_x25: Queue outgoing LAPB frames Date: Wed, 03 Mar 2021 14:26:35 +0100 Message-ID: <8cac820a181070ac2bad983dc49e4e4e@dev.tdt.de> References: <20210216201813.60394-1-xie.he.0141@gmail.com> <20210219103948.6644e61f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <906d8114f1965965749f1890680f2547@dev.tdt.de> <41b77b1c3cf1bb7a51b750faf23900ef@dev.tdt.de> <20210302153034.5f4e320b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20210302153034.5f4e320b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Jakub Kicinski Cc: Xie He , Leon Romanovsky , "David S. Miller" , Linux X25 , Linux Kernel Network Developers , LKML , Krzysztof Halasa , Jonathan Corbet , linux-doc@vger.kernel.org On 2021-03-03 00:30, Jakub Kicinski wrote: > On Tue, 02 Mar 2021 08:04:20 +0100 Martin Schiller wrote: >> On 2021-03-01 09:56, Xie He wrote: >> > On Sun, Feb 28, 2021 at 10:56 PM Martin Schiller wrote: >> >> I mean the change from only one hdlc interface to both hdlc and >> >> hdlc_x25. >> >> >> >> I can't estimate how many users are out there and how their setup >> >> looks >> >> like. >> > >> > I'm also thinking about solving this issue by adding new APIs to the >> > HDLC subsystem (hdlc_stop_queue / hdlc_wake_queue) for hardware >> > drivers to call instead of netif_stop_queue / netif_wake_queue. This >> > way we can preserve backward compatibility. >> > >> > However I'm reluctant to change the code of all the hardware drivers >> > because I'm afraid of introducing bugs, etc. When I look at the code >> > of "wan/lmc/lmc_main.c", I feel I'm not able to make sure there are no >> > bugs (related to stop_queue / wake_queue) after my change (and even >> > before my change, actually). There are even serious style problems: >> > the majority of its lines are indented by spaces. >> > >> > So I don't want to mess with all the hardware drivers. Hardware driver >> > developers (if they wish to properly support hdlc_x25) should do the >> > change themselves. This is not a problem for me, because I use my own >> > out-of-tree hardware driver. However if I add APIs with no user code >> > in the kernel, other developers may think these APIs are not >> > necessary. >> >> I don't think a change that affects the entire HDLC subsystem is >> justified, since the actual problem only affects the hdlc_x25 area. >> >> The approach with the additional hdlc_x25 is clean and purposeful >> and >> I personally could live with it. >> >> I just don't see myself in the position to decide such a change at the >> moment. >> >> @Jakub: What is your opinion on this. > > Hard question to answer, existing users seem happy and Xie's driver > isn't upstream, so the justification for potentially breaking backward > compatibility isn't exactly "strong". > > Can we cop out and add a knob somewhere to control spawning the extra > netdev? Let people who just want a newer kernel carry on without > distractions and those who want the extra layer can flip the switch? Yes, that would be a good compromise. I think a compile time selection option is enough here. We could introduce a new config option CONFIG_HDLC_X25_LEGACY (or something like that) and then implement the new or the old behavior in the driver accordingly. A switch that can be toggled at runtime (e.g. via sethdlc) would also be conceivable, but I don't think this is necessary.