From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50194) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aIfwI-0002rv-Ck for qemu-devel@nongnu.org; Mon, 11 Jan 2016 12:07:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aIfwF-0006q9-7N for qemu-devel@nongnu.org; Mon, 11 Jan 2016 12:07:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51759) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aIfwF-0006q3-2U for qemu-devel@nongnu.org; Mon, 11 Jan 2016 12:07:27 -0500 References: <1450892961-6495-1-git-send-email-vsementsov@virtuozzo.com> <568AFD50.9030006@redhat.com> <56939E25.9000309@virtuozzo.com> From: John Snow Message-ID: <5693E14D.6000708@redhat.com> Date: Mon, 11 Jan 2016 12:07:25 -0500 MIME-Version: 1.0 In-Reply-To: <56939E25.9000309@virtuozzo.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v6] spec: add qcow2 bitmaps extension specification List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, Eric Blake Cc: kwolf@redhat.com, den@openvz.org, famz@redhat.com, stefanha@redhat.com, mreitz@redhat.com On 01/11/2016 07:20 AM, Vladimir Sementsov-Ogievskiy wrote: > > Are you sure? What about creation\last change dates, file links, user > data, etc? > For now, formally, current "For now, as no extra data is defined, > extra_data_size is reserved and must be zero." is equal to such table, > but provides more flexibility for future.. Oh, I see what you're trying to do. In this case, perhaps we need a versioning system for the type-specific data? We won't be able to just add data arbitrarily, we need to change some field somewhere. Maybe we can say something like... "If extra_data_size is 0, there is no type-specific data and the version of that data layout is 0. If extra_data_size is non-zero, the first byte of the type-specific-data must be a version number greater than 0 that indicates the layout of the data to follow. For the Dirty Tracking bitmap type, only version 0 is currently valid." This way it's explicit that data *could* show up for dirty tracking in the future, but currently it does not. --js