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

Jakub Kicinski
2020-01-14T12:52:06Z

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!