From owner-freebsd-hackers@freebsd.org  Wed Oct 28 22:45:40 2015
Return-Path: <owner-freebsd-hackers@freebsd.org>
Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 2DD57A203AA
 for <freebsd-hackers@mailman.ysv.freebsd.org>;
 Wed, 28 Oct 2015 22:45:40 +0000 (UTC)
 (envelope-from koert.xls@gmail.com)
Received: from mail-lb0-f172.google.com (mail-lb0-f172.google.com
 [209.85.217.172])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (Client CN "smtp.gmail.com",
 Issuer "Google Internet Authority G2" (verified OK))
 by mx1.freebsd.org (Postfix) with ESMTPS id BF51914C8
 for <freebsd-hackers@freebsd.org>; Wed, 28 Oct 2015 22:45:39 +0000 (UTC)
 (envelope-from koert.xls@gmail.com)
Received: by lbbec13 with SMTP id ec13so16679598lbb.0
 for <freebsd-hackers@freebsd.org>; Wed, 28 Oct 2015 15:45:32 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20130820;
 h=mime-version:from:date:message-id:subject:to:content-type;
 bh=8gHmAD4RTSBshNQCCwlCckhii7SjHybuvAfrRsZqsPY=;
 b=J2AFsO28Q9JDSq0ysggnCVU1a67qL8IXiH3Jo4eDXtiI3ZbxIuxIGzu3ITwtQ0jWyh
 siV0h0wocep0i9SzjRa760T2s45wrLcFE3Q8efqk1Z6p+3II8q9JHj+CvcV0mSQk7UjJ
 XHEzYO1t2+p0AufxB9VwruwRLMDA/+LDzSZfTz5XM2/4Ko5NWQ2RsQ1xy5RbK5QTNvs0
 zRzbHwu5UlHSbLGu+vYvkVvUQv+RNBt7+OZ9/rA9LuF2s2t2J7fb/j6Qy70f92hrYIq0
 h0rhV5M13o94EzFa3vOSsa9/XhzKepjR/YyYOL26MgDyziRDiYdjWLmmR4oFo+pqw3Tw
 J/+w==
X-Received: by 10.112.199.100 with SMTP id jj4mr24861593lbc.122.1446072332396; 
 Wed, 28 Oct 2015 15:45:32 -0700 (PDT)
MIME-Version: 1.0
From: Koert van der Veer <koert@cloudvps.com>
Date: Wed, 28 Oct 2015 22:45:22 +0000
Message-ID: <CAHRLrwNcLPrztuVvhrRj3Ya=Aw-5eDMRGD=L0wwVzfmPgQXwCQ@mail.gmail.com>
Subject: ABI stability for loadable modules
To: freebsd-hackers@freebsd.org
X-Mailman-Approved-At: Wed, 28 Oct 2015 23:17:29 +0000
Content-Type: text/plain; charset=UTF-8
X-Content-Filtered-By: Mailman/MimeDel 2.1.20
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.20
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 28 Oct 2015 22:45:40 -0000

TL;DR: Can I safely load a kernel module compiled against a slightly
different kernel?


I maintain a fleet of FreeBSD machines. We've encountered a problem with
one of the modules (iscsi doesn't allow passwords > 16 chars). I've
determined that patching the module solves the problem for us, and doesn't
affect any other kernel component. I'd like to distribute the patched
module and user-space components. My use-case allows me to unload the iscsi
module, but doesn't allow me to reboot the machine.


However, we're running an array of different kernels (10.0-RELEASE,
10.0-RELEASE-p9, 10.0-STABLE, 10.1-RELEASE, 10.1-RELEASE-p6). I'd like to
minimize the number of distinct binaries being distributed, so preferably
I'd compile only one or two. My preliminary tests on VMs show me that this
does not cause any immediate problems. Is this actually safe, or do I need
to make distinct sets of binaries for each minor version and patchlevel of
kernel in production?