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Date:   Tue, 14 Jan 2020 14:33:51 +0100
From:   Martin Schiller <ms@dev.tdt.de>
To:     Jakub Kicinski <kubakici@wp.pl>
Cc:     khc@pm.waw.pl, davem@davemloft.net, linux-x25@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] wan/hdlc_x25: make lapb params configurable
Organization: TDT AG
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On 2020-01-14 13:51, Jakub Kicinski wrote:
> On Tue, 14 Jan 2020 06:37:03 +0100, Martin Schiller wrote:
>> >> diff --git a/include/uapi/linux/hdlc/ioctl.h
>> >> b/include/uapi/linux/hdlc/ioctl.h
>> >> index 0fe4238e8246..3656ce8b8af0 100644
>> >> --- a/include/uapi/linux/hdlc/ioctl.h
>> >> +++ b/include/uapi/linux/hdlc/ioctl.h
>> >> @@ -3,7 +3,7 @@
>> >>  #define __HDLC_IOCTL_H__
>> >>
>> >>
>> >> -#define GENERIC_HDLC_VERSION 4	/* For synchronization with sethdlc
>> >> utility */
>> >> +#define GENERIC_HDLC_VERSION 5	/* For synchronization with sethdlc
>> >> utility */
>> >
>> > What's the backward compatibility story in this code?
>> 
>> Well, I thought I have to increment the version to keep the kernel 
>> code
>> and the sethdlc utility in sync (like the comment says).
> 
> Perhaps I chose the wrong place for asking this question, IOCTL code
> was my real worry. I don't think this version number is validated so
> I think bumping it shouldn't break anything?

sethdlc validates the GENERIC_HDLC_VERSION at compile time.

https://mirrors.edge.kernel.org/pub/linux/utils/net/hdlc/

Another question:
Where do I have to send my patch for sethdlc to?

> 
>> > The IOCTL handling at least looks like it may start returning errors
>> > to existing user space which could have expected the parameters to
>> > IF_PROTO_X25 (other than just ifr_settings.type) to be ignored.
>> 
>> I could also try to implement it without incrementing the version by
>> looking at ifr_settings.size and using the former defaults if the size
>> doesn't match.
> 
> Sounds good, thank you!

OK, I will send a v2 of the patch.