From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55766) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aJ0kp-0001Qt-Kf for qemu-devel@nongnu.org; Tue, 12 Jan 2016 10:21:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aJ0ko-0005mD-FG for qemu-devel@nongnu.org; Tue, 12 Jan 2016 10:21:03 -0500 Date: Tue, 12 Jan 2016 16:20:51 +0100 From: Kevin Wolf Message-ID: <20160112152051.GG4841@noname.redhat.com> References: <1452578622-4492-1-git-send-email-den@openvz.org> <20160112141607.GD4841@noname.redhat.com> <569514E7.8090101@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <569514E7.8090101@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/1] blk: do not select PFLASH device for internal snapshot List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: "Denis V. Lunev" , Laszlo Ersek , qemu-devel@nongnu.org, qemu-block@nongnu.org Am 12.01.2016 um 15:59 hat Paolo Bonzini geschrieben: > > > On 12/01/2016 15:16, Kevin Wolf wrote: > >> Thus we should avoid selection of "pflash" drives for VM state saving. > >> > >> For now "pflash" is read-write raw image as it configured by libvirt. > >> Thus there are no such images in the field and we could safely disable > >> ability to save state to those images inside QEMU. > > > > This is obviously broken. If you write to the pflash, then it needs to > > be snapshotted in order to keep a consistent state. > > > > If you want to avoid snapshotting the image, make it read-only and it > > will be skipped even today. > > Sort of. The point of having flash is to _not_ make it read-only, so > that is not a solution. > > Flash is already being snapshotted as part of saving RAM state. In > fact, for this reason the device (at least the one used with OVMF; I > haven't checked other pflash devices) can simply save it back to disk > on the migration destination, without the need to use "migrate -b" or > shared storage. > [...] > I don't like very much using IF_PFLASH this way, which is why I hadn't > replied to the patch so far---I hadn't made up my mind about *what* to > suggest instead, or whether to just accept it. However, it does work. > > Perhaps a separate "I know what I am doing" skip-snapshot option? Or > a device callback saying "not snapshotting this is fine"? Boy, is this ugly... What do you do with disk-only snapshots? The recovery only works as long as you have VM state. Kevin