From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50497) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b04iK-00055D-Kr for qemu-devel@nongnu.org; Tue, 10 May 2016 06:16:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b04iH-000473-BE for qemu-devel@nongnu.org; Tue, 10 May 2016 06:16:28 -0400 Date: Tue, 10 May 2016 11:16:12 +0100 From: "Richard W.M. Jones" Message-ID: <20160510101612.GY1683@redhat.com> References: <1462848659-28659-1-git-send-email-famz@redhat.com> <20160510081425.GV1683@redhat.com> <20160510084303.GB28935@redhat.com> <20160510085041.GC13377@redhat.com> <20160510091422.GG4921@noname.str.redhat.com> <20160510092338.GG13377@redhat.com> <20160510093514.GH4921@noname.str.redhat.com> <20160510094310.GH13377@redhat.com> <20160510100706.GJ4921@noname.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160510100706.GJ4921@noname.str.redhat.com> Subject: Re: [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: "Daniel P. Berrange" , Fam Zheng , qemu-block@nongnu.org, Jeff Cody , Markus Armbruster , qemu-devel@nongnu.org, stefanha@redhat.com, pbonzini@redhat.com, den@openvz.org, Max Reitz , John Snow On Tue, May 10, 2016 at 12:07:06PM +0200, Kevin Wolf wrote: > I'm surprised how low the standards seem to be when we're talking about > data integrity. If occasionally losing data is okay, the qemu block > layer could be quite a bit simpler. I welcome this patch because it fixes a real data integrity issue which we've seen in the field: people using guestfish (in write mode) on live VMs. We try our very best to prevent this happening -- for example if you use guestfish via libvirt, it will check if the VM is live and refuse access. Though this is not and cannot be bulletproof (since someone can start a VM up after we have opened it). We also have prominent warnings in the manual and in the FAQ about this. However _reading_ disks doesn't corrupt live VMs. The worst that happens is guestfish will error out or you'll see some inconsistent stats from virt-df. None of this has anything to do with data integrity in the qemu block layer, and no one is arguing that it should be weakened. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top