ABI changes within stable branch

[Mark Linimon]

On Tue, Sep 19, 2017 at 07:33:20PM -0600, Warner Losh wrote:
> FreeBSD has always had a policy of backwards compatibility. By that
> definition we are stable. What we don't promise is full forwards
> compatibility, which is what you are asking for.

In particular, "we add things to the ABI" sometimes changes the way
packages build (e.g. if a config script auto-detects the change).
Because of this, you have to be very particular that you are running
either 11.0-built things, or 11.1-built things, but not a combination.

If you're running 11.X-stable across the thing-added-to-ABI boundary,
then you can get into the same bad state.

Ports rarely get into that state across that boundary, and only a few
of them, but it is very annoying when it does happen (e.g. rsync).

The only way to make sure that doesn't happen is to cancel the developers'
ability to modify the ABI in any way.  Unfortunately, I don't see that
happening.

mcl