From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MWFDN-0007Uw-7J for qemu-devel@nongnu.org; Wed, 29 Jul 2009 15:53:29 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MWFDI-0007S9-HO for qemu-devel@nongnu.org; Wed, 29 Jul 2009 15:53:28 -0400 Received: from [199.232.76.173] (port=49023 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MWFDI-0007S6-A0 for qemu-devel@nongnu.org; Wed, 29 Jul 2009 15:53:24 -0400 Received: from mx20.gnu.org ([199.232.41.8]:40277) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MWFDH-0003py-Fg for qemu-devel@nongnu.org; Wed, 29 Jul 2009 15:53:23 -0400 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MWFDG-00033j-6i for qemu-devel@nongnu.org; Wed, 29 Jul 2009 15:53:22 -0400 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH v2] make windows notice media change Date: Wed, 29 Jul 2009 20:52:35 +0100 References: <20090729120719.GN30449@redhat.com> <5b31733c0907291218k624f97bbx62d8d6d49b8f0759@mail.gmail.com> <5b31733c0907291224h340921f0j72195618b0b6cd2a@mail.gmail.com> In-Reply-To: <5b31733c0907291224h340921f0j72195618b0b6cd2a@mail.gmail.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200907292052.35755.paul@codesourcery.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Filip Navara , Gleb Natapov > >>> Why shouldn't we support loading version 2 snapshots? Afterall that's > >>> why we had the versioning in the first place. > >> > >> No it's not. Versioning was introduced to *prevent* loading old > >> snapshots and crashing or ending up with inconsistent guest state. I'm > >> still unconvinced that anything other than very short term backward > >> compatibility is worthwhile or even viable. > > > > I see it as a way to migrate a running guest to newer QEMU version, > > possibly even with live migration. In fact I used it quite often back in > > the day when snapshots were not part of qcow2 yet and when kqemu was > > still in its heydays. > > BTW, why would there be the version parameter in the first place if it > wasn't supposed to load older versions?! Like I already said: it's there to prevent an old version being loaded accidentally. Without this an incompatible change will result in anything from a crash to corrupt/inconsistent guest state. Versioning allows us to reject the snapshot and fail safely. Paul