From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45560) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsBZp-00040u-PX for qemu-devel@nongnu.org; Thu, 27 Jun 2013 08:45:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UsBZn-0002PU-SD for qemu-devel@nongnu.org; Thu, 27 Jun 2013 08:45:29 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:43014) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsBZn-0002OL-81 for qemu-devel@nongnu.org; Thu, 27 Jun 2013 08:45:27 -0400 Received: from /spool/local by e28smtp03.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 27 Jun 2013 18:09:18 +0530 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by d28dlp03.in.ibm.com (Postfix) with ESMTP id 289571258059 for ; Thu, 27 Jun 2013 18:14:24 +0530 (IST) Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r5RCjSVX25100404 for ; Thu, 27 Jun 2013 18:15:29 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r5RCj61X009946 for ; Thu, 27 Jun 2013 22:45:06 +1000 Message-ID: <51CC33A6.2080206@linux.vnet.ibm.com> Date: Thu, 27 Jun 2013 20:44:22 +0800 From: Wenchao Xia MIME-Version: 1.0 References: <51C2C465.1090701@linux.vnet.ibm.com> <20130625091300.GA26177@stefanha-thinkpad.redhat.com> <51C97B8B.2010304@linux.vnet.ibm.com> <20130627090139.GC14351@stefanha-thinkpad.redhat.com> In-Reply-To: <20130627090139.GC14351@stefanha-thinkpad.redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC] qemu-img: add option -d in convert List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , Paolo Bonzini , Anthony Liguori , qemu-devel , Dietmar Maurer 于 2013-6-27 17:01, Stefan Hajnoczi 写道: > On Tue, Jun 25, 2013 at 07:14:19PM +0800, Wenchao Xia wrote: >> 于 2013-6-25 17:13, Stefan Hajnoczi 写道: >>> On Thu, Jun 20, 2013 at 04:59:17PM +0800, Wenchao Xia wrote: >>> >>> If I understand correctly, you have a backing chain with internal >>> snapshots: >>> >>>> imageA(sn0)->imageB(sn0,sn1)->imageC(sn0) >>> >>> And you want to convert this to a chain of external snapshots: >>> >> What it looks like is convert into external snapshots, actually >> requirement is get delta data from internal snapshot, external snapshots >> have delta data by nature so it is a way to orginize it. This patch >> will help get that delta data. > > Copying all the data out into external files in order to get > is_allocated information seems very inefficient. > Forget to say, my purpose is not get is_allocated info, but get the different data between two snapshots or images. Now qemu-img can do it in-directly as the example shows, the -d option will make it simpler and faster. for example imageA(sn0, sn1, sn2), it will help to get different data between sn0 and sn2. An alternative way is let qemu-nbd export sn0 and sn2, then user diff the data itself, but we lost the chance to use L1/L2 table , allocated info, to accelerate it. > We've discussed dirty block tracking APIs on the list several times. > This seems related. > > Maybe it's time to tackle this properly for both external and internal > snapshots. > > The reason why a dirty block tracking API is also helpful is that not > all tools want to learn how to open different image file formats. (Even > with libqblock.) > > The drity block tracking API gives them information which they can use > together with a single interface like NBD or a libvirt block pread-style > interface to read out dirty blocks. > > BTW we already have qemu-io -c map which prints out allocation > information for an image file. If that command is extended to support > -s then you can get your info easily. > > Stefan > -- Best Regards Wenchao Xia