From owner-svn-src-stable-9@FreeBSD.ORG Sat Dec 29 14:58:05 2012 Return-Path: Delivered-To: svn-src-stable-9@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 99D2DEC9; Sat, 29 Dec 2012 14:58:05 +0000 (UTC) (envelope-from adrian.chadd@gmail.com) Received: from mail-wg0-f54.google.com (mail-wg0-f54.google.com [74.125.82.54]) by mx1.freebsd.org (Postfix) with ESMTP id 512508FC08; Sat, 29 Dec 2012 14:58:04 +0000 (UTC) Received: by mail-wg0-f54.google.com with SMTP id fg15so5079567wgb.21 for ; Sat, 29 Dec 2012 06:57:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=ohG/2eRmm3x2jgpTj7MGBBbveOD8RTz+7jj7NNxW3O8=; b=Kb6jv91M2V3gDe3UqJWyWnxDu6atg+KCB3YP87oi9j0vdIKTimXm9tSwVNnLzs91iz +Kq7HHY2a9/j5/6DMHTSmwIpnqJccn5dF/TT4SgRxB7/cxKVpVEo21lWuUZij3z/tec7 PxeUH6dCpUyondW+6JPKkw2TN45n5DKd3lOBBZaXYbSF3CcyTWGb1YZqNWKxNuu07euH fACeNBd9Vvz3mSA4GkG8yCrwJ2yiD2/kT0pCCYoAFu3xFUmb7/VloI886vCb/zBYU5tt 8xBoHbCtEGxbgFUYApxmXfMQG5kmatU71PL/wA02cmMtl7Q3dAfYiw5SCJOc3Yy0zPKO 9Bfw== MIME-Version: 1.0 Received: by 10.180.72.146 with SMTP id d18mr48368754wiv.33.1356792654354; Sat, 29 Dec 2012 06:50:54 -0800 (PST) Sender: adrian.chadd@gmail.com Received: by 10.217.57.9 with HTTP; Sat, 29 Dec 2012 06:50:54 -0800 (PST) In-Reply-To: <00E4FFFA-8ADB-4D43-B977-3834C48133E4@freebsd.org> References: <201212241422.qBOEMrcF021632@svn.freebsd.org> <50D8B533.8080507@mu.org> <20121225104422.GB53644@kib.kiev.ua> <00E4FFFA-8ADB-4D43-B977-3834C48133E4@freebsd.org> Date: Sat, 29 Dec 2012 06:50:54 -0800 X-Google-Sender-Auth: yQPqxdeVuxt9H4olrOLWZ3j89kA Message-ID: Subject: Re: svn commit: r244663 - stable/9 From: Adrian Chadd To: "Robert N. M. Watson" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: src-committers@freebsd.org, svn-src-stable@freebsd.org, svn-src-all@freebsd.org, Alfred Perlstein , svn-src-stable-9@freebsd.org, Konstantin Belousov X-BeenThere: svn-src-stable-9@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: SVN commit messages for only the 9-stable src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 29 Dec 2012 14:58:05 -0000 On 29 December 2012 02:44, Robert N. M. Watson wrote: [snip] >> [adrian chadd] >> So, regardless of whether we should or shouldn't break things, a more >> thorough discussion would've been nice. > > Adrian: > > The standing consensus is that we try not to break certain classes of dev= ice drivers, not that we don't ever change any kernel interfaces. The reaso= n is that we don't have a formal definition of "public" and do not wish to = use the definition "all definitions in all header files" or "all symbols ev= er linked by any module" -- that definition would prevent almost any change= to the kernel in -STABLE branches at all. The reason VIMAGE/MRT/etc had to= be done with great caution is that they directly affected network device d= rivers, which are a category of module which we have decided we do want to = try to support in external binary form. The other major category is binary = storage drivers. > > When we talked to various VFS maintainers, looked at the past change hist= ory there, and looked at the set of third-party file systems (especially, t= hose we could see in ports), the consensus there was that it was too diffic= ult to define a stable VFS KPI and KBI for third-party modules. In particul= ar, there appear to be at most one or two in ports at any given moment, and= quick analyses of them suggested that their kernel feature dependency foot= print was far more than just "vnode operations". > > KPIs and KBIs have benefits and downsides: we need to consider them as a = tradeoff space, and not an absolute, and use them where they have significa= nt payoff. Especially as we don't have formal tools for reasoning about or = testing them. Sure, that's a logical, reasoned analysis of what the state of play of the VFS interface and users. But again, it'd have been nice to get some notification before it was pushed to -stable, just as a heads up (and a chance for feedback) for people and companies who aren't on your radar. Adrian