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Date:      Sat, 3 Mar 2001 16:31:14 -0800
From:      Kris Kennaway <kris@obsecurity.org>
To:        "Louis A. Mamakos" <louie@TransSys.COM>
Cc:        Danny Braniss <danny@cs.huji.ac.il>, FreeBSD-stable <freebsd-stable@FreeBSD.ORG>
Subject:   Re: wchan kqread
Message-ID:  <20010303163114.B51808@mollari.cthul.hu>
In-Reply-To: <200103040020.f240KQW50170@whizzo.transsys.com>; from louie@TransSys.COM on Sat, Mar 03, 2001 at 07:20:26PM -0500
References:  <E14ZEFk-0001da-00@cs.huji.ac.il> <20010303144716.A33685@mollari.cthul.hu> <200103040020.f240KQW50170@whizzo.transsys.com>

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On Sat, Mar 03, 2001 at 07:20:26PM -0500, Louis A. Mamakos wrote:
> > On Sat, Mar 03, 2001 at 05:47:28PM +0200, Danny Braniss wrote:
> > > i did, but did not compile it :-), since all i did was to reconfigure=
 a kernel.
> > >=20
> > > now it works again. thanks!
> > >=20
> > > btw, what is the way of knowing when a change in the kernel affects u=
serland
> > > programs?=20
> >=20
> > You can't, but you're expected to build a new world each time you
> > update your kernel sources. The kernel and userland are an inseparable
> > whole, and you'll generally have weird problems if you only do one or
> > the other.
>=20
> Uh, I certainly hope not.
>=20
> My understanding is that the kernel interfaces are generally upwards
> compatible; that is, you can most to a newer kernel without major=20
> impact to existing userland software.  If this upwards compatability
> isn't working, then that's a bug.

This has never been the case; the main culprits are things like top
and ps which rely (relied - it's fixed in -current) on struct proc
which changes size fairly regularly, but there are others.  We're
trying to move away from that by more sensible exporting of data
structures, but this is the way it's always been.

In this case however, it wasn't a backwards compatability problem
since libc was trying to use new kernel features, namely new kqueue
features.

Kris

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