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

[Martin Schiller]

On 2021-02-19 21:28, Xie He wrote:
> On Fri, Feb 19, 2021 at 10:39 AM Jakub Kicinski <kuba@xxxxxxxxxx> 
> wrote:
> > Not entirely sure what the argument is about but adding constants 
> > would
> > certainly help.
>
> Leon wants me to replace this:
>
> dev->needed_headroom = 3 - 1;
>
> with this:
>
> /* 2 is the result of 3 - 1 */
> dev->needed_headroom = 2;
>
> But I don't feel his way is better than my way.
>
> > More fundamentally IDK if we can make such a fundamental change here.
> > When users upgrade from older kernel are all their scripts going to
> > work the same? Won't they have to bring the new netdev up?
>
> Yes, this patch will break backward compatibility. Users with old
> scripts will find them no longer working.
>
> However, it's hard for me to find a better way to solve the problem
> described in the commit message.
>
> So I sent this as an RFC to see what people think about this. (Martin
> Schiller seems to be OK with this.)

Well, I said I would like to test it.

I'm not really happy with this change because it breaks compatibility.
We then suddenly have 2 interfaces; the X.25 routings are to be set via
the "new" hdlc<x>_x25 interfaces instead of the hdlc<x> interfaces.

I currently just don't have a nicer solution to fix this queueing
problem either. On the other hand, since the many years we have been
using the current state, I have never noticed any problems with
discarded frames. So it might be more a theoretical problem than a
practical one.


> I think users who don't use scripts can adapt quickly and users who
> use scripts can also trivally fix their scripts.
>
> Actually many existing commits in the kernel also (more or less) cause
> some user-visible changes. But I admit this patch is a really big
> change.