From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:45602) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RFkWc-0003VP-3E for qemu-devel@nongnu.org; Mon, 17 Oct 2011 06:34:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RFkWZ-0001Av-Px for qemu-devel@nongnu.org; Mon, 17 Oct 2011 06:34:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5238) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RFkWZ-0001Al-Iv for qemu-devel@nongnu.org; Mon, 17 Oct 2011 06:34:27 -0400 Message-ID: <4E9C04AB.6000003@redhat.com> Date: Mon, 17 Oct 2011 12:34:19 +0200 From: Avi Kivity MIME-Version: 1.0 References: <1318387026-21569-1-git-send-email-david@gibson.dropbear.id.au> <4E9AAA33.3010806@redhat.com> <20111016114011.GG4580@truffala.fritz.box> <4E9ACF99.9020507@redhat.com> <20111017053153.GB30114@truffala.fritz.box> In-Reply-To: <20111017053153.GB30114@truffala.fritz.box> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] Memory API bugfix - abolish addrrrange_end() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws, agraf@suse.de, aik@ozlabs.ru, qemu-devel@nongnu.org On 10/17/2011 07:31 AM, David Gibson wrote: > > > > In terms of how the code looks, it's seriously more ugly (see the > > patches I sent out). Conceptually it's cleaner, since we're not dodging > > the issue that we need to deal with a full 64-bit domain. > > We don't have to dodge that issue. I know how to remove the > requirement for intermediate negative values, I just haven't made up a > patch yet. With that we can change to uint64 and cover the full 64 > bit range. In fact I think I can make it so that size==0 represents > size=2^64 and even handle the full 64-bit, inclusive range properly. That means you can't do a real size == 0. > > But my main concern is maintainability. The 64-bit blanket is to short, > > if we keep pulling it in various directions we'll just expose ourselves > > in new ways. > > Nonsense, dealing with full X-bit range calculations in X-bit types is > a fairly standard problem. The kernel does it in VMA handling for > one. It just requires thinking about overflow cases. We discovered three bugs already (you found two, and I had one during development). Even if it can probably be done with extreme care, but is it worth spending all that development time on? I'm not sure there is a parallel with vmas, since we're offsetting in both the positive and negative directions. -- error compiling committee.c: too many arguments to function