On Wed, Mar 3, 2021 at 5:26 AM Martin Schiller [off-list ref] wrote:

On 2021-03-03 00:30, Jakub Kicinski wrote:

quoted

Hard question to answer, existing users seem happy and Xie's driver
isn't upstream, so the justification for potentially breaking backward
compatibility isn't exactly "strong".

Can we cop out and add a knob somewhere to control spawning the extra
netdev? Let people who just want a newer kernel carry on without
distractions and those who want the extra layer can flip the switch?

Yes, that would be a good compromise.
I think a compile time selection option is enough here.
We could introduce a new config option CONFIG_HDLC_X25_LEGACY (or
something like that) and then implement the new or the old behavior in
the driver accordingly.

A switch that can be toggled at runtime (e.g. via sethdlc) would also be
conceivable, but I don't think this is necessary.

Yes, I think adding a new config option would be a good way. Thank you both!!