netdev - Re: [PATCH net-next RFC v4] net: hdlc_x25: Queue outgoing LAPB frames

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Date:   Tue, 02 Mar 2021 08:04:20 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Xie He <xie.he.0141@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Linux X25 <linux-x25@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Krzysztof Halasa <khc@...waw.pl>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next RFC v4] net: hdlc_x25: Queue outgoing LAPB frames

On 2021-03-01 09:56, Xie He wrote:
> On Sun, Feb 28, 2021 at 10:56 PM Martin Schiller <ms@....tdt.de> wrote:
>> 
>> >> Also, I have a hard time assessing if such a wrap is really
>> >> enforceable.
>> >
>> > Sorry. I don't understand what you mean. What "wrap" are you referring
>> > to?
>> 
>> I mean the change from only one hdlc<x> interface to both hdlc<x> and
>> hdlc<x>_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<x>_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.