From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36134) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V16mC-0002w9-0b for qemu-devel@nongnu.org; Sun, 21 Jul 2013 23:27:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V16mA-0003uv-Vt for qemu-devel@nongnu.org; Sun, 21 Jul 2013 23:27:07 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:46943) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V16mA-0003u7-Cv for qemu-devel@nongnu.org; Sun, 21 Jul 2013 23:27:06 -0400 Received: from /spool/local by e28smtp09.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 22 Jul 2013 08:51:50 +0530 Received: from d28relay04.in.ibm.com (d28relay04.in.ibm.com [9.184.220.61]) by d28dlp01.in.ibm.com (Postfix) with ESMTP id D8431E004F for ; Mon, 22 Jul 2013 08:56:59 +0530 (IST) Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay04.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r6M3Qu8T28377154 for ; Mon, 22 Jul 2013 08:56:57 +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 r6M3R0rR005711 for ; Mon, 22 Jul 2013 13:27:00 +1000 Message-ID: <51ECA679.9040700@linux.vnet.ibm.com> Date: Mon, 22 Jul 2013 11:26:49 +0800 From: Wenchao Xia MIME-Version: 1.0 References: <1374069835-14287-1-git-send-email-xiawenc@linux.vnet.ibm.com> <20130718054350.GE26971@stefanha-thinkpad.redhat.com> <51E900D3.30705@linux.vnet.ibm.com> <20130722021057.GA25622@T430s.nay.redhat.com> In-Reply-To: <20130722021057.GA25622@T430s.nay.redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH 0/4] export internal snapshot by qemu-nbd List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: famz@redhat.com Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, Stefan Hajnoczi , dietmar@proxmox.com 于 2013-7-22 10:10, Fam Zheng 写道: > On Fri, 07/19 17:03, Wenchao Xia wrote: >> 于 2013-7-18 13:43, Stefan Hajnoczi 写道: >>> On Wed, Jul 17, 2013 at 10:03:51PM +0800, Wenchao Xia wrote: >>>> This series allow user to read internal snapshot's contents without qemu-img >>>> convert. Another purpose is that, when qemu is online and have taken an >>>> internal snapshot, let user invoke qemu-nbd to do any thing on it except write. >>> >>> I agree with Eric and Kevin that we cannot access image files while QEMU >>> has them open. >>> >>> A bit more detail about using the run-time NBD server to do this safely: >>> >>> Internal snapshots are not first-class block layer objects today. They >>> are not BlockDriverStates, instead you must access their data through >>> bdrv_snapshot_goto() or bdrv_snapshot_load_tmp(). >>> >> Also cc to Fam Zheng an Kevin: >> I think BlockDriverStates modification, is based on a more basic >> question: does qcow2's data structure on disk, allow multiple snapshot >> reader, while one active writer, without lock? I think the modification >> showed above, already said "yes" to this question. If yes, just >> create a new BlockDriverStates, we should say yes in spec. >> I wonder how vmdk allow direct snapshot access by VixDiskLib 1.1, >> without network expense on host, it should be the format said support >> of it. >> > Is the VMDK snapshot internal? Which subformat of VMDK do you mean here? > > Thanks. > Rechecked VMDK's doc, guess it is using backing chain. Still, It helps if internal snapshot can do similar things. -- Best Regards Wenchao Xia