From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51765) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V15dg-0003OW-JE for qemu-devel@nongnu.org; Sun, 21 Jul 2013 22:14:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V15dd-00070C-2l for qemu-devel@nongnu.org; Sun, 21 Jul 2013 22:14:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:30387) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V15dc-0006zt-RD for qemu-devel@nongnu.org; Sun, 21 Jul 2013 22:14:13 -0400 Date: Mon, 22 Jul 2013 10:10:57 +0800 From: Fam Zheng Message-ID: <20130722021057.GA25622@T430s.nay.redhat.com> References: <1374069835-14287-1-git-send-email-xiawenc@linux.vnet.ibm.com> <20130718054350.GE26971@stefanha-thinkpad.redhat.com> <51E900D3.30705@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <51E900D3.30705@linux.vnet.ibm.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 0/4] export internal snapshot by qemu-nbd Reply-To: famz@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wenchao Xia Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, Stefan Hajnoczi , dietmar@proxmox.com On Fri, 07/19 17:03, Wenchao Xia wrote: > =E4=BA=8E 2013-7-18 13:43, Stefan Hajnoczi =E5=86=99=E9=81=93: > >On Wed, Jul 17, 2013 at 10:03:51PM +0800, Wenchao Xia wrote: > >>This series allow user to read internal snapshot's contents without q= emu-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 exc= ept write. > > > >I agree with Eric and Kevin that we cannot access image files while QE= MU > >has them open. > > > >A bit more detail about using the run-time NBD server to do this safel= y: > > > >Internal snapshots are not first-class block layer objects today. The= y > >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. >=20 Is the VMDK snapshot internal? Which subformat of VMDK do you mean here? Thanks. --=20 Fam