Re: [PATCH 1/2] wan/hdlc_x25: make lapb params configurable

From: Martin Schiller
Date: Tue Jan 14 2020 - 08:33:58 EST


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.