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Date:   Tue, 14 Jan 2020 04:51:49 -0800
From:   Jakub Kicinski <kubakici@wp.pl>
To:     Martin Schiller <ms@dev.tdt.de>
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
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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?

> > 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!