Re: Minor sysupgrade issue

[David Brownlee <abs%absd.org@localhost>]

On Sun, 2 Jun 2024 at 00:06, Brad Spencer <brad%anduin.eldar.org@localhost> wrote:
>
> Chavdar Ivanov <ci4ic4%gmail.com@localhost> writes:
>
> [snip]
>
> >                                              But then wouldn't be
> > there a chance that the old userland disagrees with the new kernel?
> >
>
>
> As a general statement, that should not be a problem as long as the
> kernel has the COMPAT_* options set.
>
> My own personal experience is that since about 1995, I have encountered
> exactly two instances where the newer kernel would not run the older
> userland completely correctly assuming the new kernel had the COMPAT_*
> options.  One was very early where some programs from a 0.9 userland had
> trouble with a 1.0 kernel.  I never understood what was going on, and a
> recompile of the programs fixed them.  The second was around the 4.x -
> 6.x time frame where a system call was removed completely and old
> userland had trouble.  So if you were going from 4.x to something more
> recent, you might have some problems especially with pkgsrc.

Probably the removal of scheduler activation threads around netbsd-5,
which were a very efficient (but unfortunately also very complicated)
way to implement userland threads. :)

David