Re: git: 2c1963d46335 - main - procfs rlimit: handle pipebuf [and related] :pipebuf . . . Invalid argument

On Sun, Oct 6, 2024 at 3:09 AM Konstantin Belousov <kostikbel@gmail.com>
wrote:

> On Sun, Oct 06, 2024 at 10:57:23AM +0200, Dag-Erling Smørgrav wrote:
> > Konstantin Belousov <kostikbel@gmail.com> writes:
> > > We do not provide forward compatibility between kernel and userspace.
> > > User binaries must be newer than kernel.
> >
> > Uh, no.  The opposite, in fact.
>
> Right, it is opposite.  It was a typo.
>
> Anyway, __FreeBSD_version is not about compatibility between specific
> snapshot of kernel and user sources.  It de-facto provides two technical
> measures:
> 1. kernel refuses to load modules built against headers set with higher
>    __FreeBSD_version than kernel
> 2. Some values of __FreeBSD_version are used by userspace to
>    detect if specific change is present in kernel.  See sys/param.h
>    P_OSREL_ list.
>

3. It's used extensively in 3rd party software to select different
interfaces
(including ports). That's why we document why we do each bump.

While 'forward compatibility' is sometimes needed / provided when it
adversely affects upgrade from source and fall back to prior kernel while
it's worked out. But (a) ZFS BEs eliminate many problems and (b) we've
only done it when it was impossible to run buildkernel / git (or svn or cvs
in the past) to fix the problem. While the messages are annoying, they
don't prevent that limited exception we've occasionally done in the past.
In general, we've avoided changes so incompatible that they've needed
a new P_OSREL_ entry to cope...

Warner