Re: CVS commit: src/sys/sys

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Thu, 13 Nov 2025 14:02:12 +0100
    From:        Jörg Sonnenberger <joerg%bec.de@localhost>
    Message-ID:  <c807a6f5-eb9e-456b-913c-22a14e81c9e9%bec.de@localhost>

  | [Me...]
  | > That define is for internal kernel ABI changes (and should really almost
  | > never be tested by anything in userland.)
  |
  | There is a lot historic precedence for using exactly this approach.

Yes, I know, it has always been wrong, the kernel version is
too crude to keep track of all changes that affect userland,
and if we tried to make it so, we'd be bumping it every day,
perhaps several times.

This case is one of the less clear, az it affects a kernel include
file, and so can be kind of assumed to be in sync with sys/param.h
though why this particular definition is there rather than in
tbe userland equivalent header which userland should be using
(which includes the kernel one for the shared definitions) I have
no idea - clearly the kernel doesn't use it, as no kernel changes
were needed when it altered.

But in general, we do not assume that userland is updated with
every updated kernel, whether or not __NetBSD_Version__ changes.
So using that define to guess at userland features can't in
general be expected to work.

We should, all, get used to dealing with this issue properly.
Always make sure some compile time testable symbol changes
whenever some feature visible to userland is added/removed/altered.

kre