From patchwork Wed Jan 4 14:08:58 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marcelo Tosatti X-Patchwork-Id: 134257 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 67A231007D7 for ; Thu, 5 Jan 2012 01:12:43 +1100 (EST) Received: from localhost ([::1]:59454 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiRa2-0002Cy-ES for incoming@patchwork.ozlabs.org; Wed, 04 Jan 2012 09:12:38 -0500 Received: from eggs.gnu.org ([140.186.70.92]:45851) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiRZO-0000Rr-DP for qemu-devel@nongnu.org; Wed, 04 Jan 2012 09:12:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RiRZC-0001cl-Vc for qemu-devel@nongnu.org; Wed, 04 Jan 2012 09:11:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24009) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiRZC-0001cO-NX for qemu-devel@nongnu.org; Wed, 04 Jan 2012 09:11:46 -0500 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q04EBijN007040 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 4 Jan 2012 09:11:44 -0500 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx02.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id q04EBh1w003058; Wed, 4 Jan 2012 09:11:43 -0500 Received: from amt.cnet (vpn-9-110.rdu.redhat.com [10.11.9.110]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id q04EBgPC019656; Wed, 4 Jan 2012 09:11:42 -0500 Received: from amt.cnet (amt.cnet [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id D4F75652355; Wed, 4 Jan 2012 12:10:56 -0200 (BRST) Received: (from marcelo@localhost) by amt.cnet (8.14.5/8.14.5/Submit) id q04EAt4W019604; Wed, 4 Jan 2012 12:10:55 -0200 Message-Id: <20120104140945.802506060@redhat.com> User-Agent: quilt/0.48-1 Date: Wed, 04 Jan 2012 12:08:58 -0200 From: Marcelo Tosatti To: stefanha@linux.vnet.ibm.com, kwolf@redhat.com, qemu-devel@nongnu.org References: <20120104140854.631720304@redhat.com> Content-Disposition: inline; filename=live-block-operations X-Scanned-By: MIMEDefang 2.67 on 10.5.11.12 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) X-Received-From: 209.132.183.28 Cc: Marcelo Tosatti Subject: [Qemu-devel] [patch 4/4] add doc to describe live block operations X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Signed-off-by: Marcelo Tosatti Index: stefanha/docs/live-block-ops.txt =================================================================== --- /dev/null +++ stefanha/docs/live-block-ops.txt @@ -0,0 +1,58 @@ +LIVE BLOCK OPERATIONS +===================== + +High level description of live block operations. Note these are not +supported for use with the raw format at the moment. + +Snapshot live merge +=================== + +Given a snapshot chain, described in this document in the following +format: + +[A] -> [B] -> [C] -> [D] + +Where the rightmost object ([D] in the example) described is the current +image which the guest OS has write access to. To the left of it is its base +image, and so on accordingly until the leftmost image, which has no +base. + +The snapshot live merge operation transforms such a chain into a +smaller one with fewer elements, such as this transformation relative +to the first example: + +[A] -> [D] + +Currently only forward merge with target being the active image is +supported, that is, data copy is performed in the right direction with +destination being the rightmost image. + +The operation is implemented in QEMU through image streaming facilities. + +The basic idea is to execute 'block_stream virtio0' while the guest is +running. Progress can be monitored using 'info block-jobs'. When the +streaming operation completes it raises a QMP event. 'block_stream' +copies data from the backing file(s) into the active image. When finished, +it adjusts the backing file pointer. + +The 'base' parameter specifies an image which data need not be streamed from. +This image will be used as the backing file for the active image when the +operation is finished. + +In the example above, the command would be: + +(qemu) block_stream virtio0 A + + +Live block copy +=============== + +To copy an in use image to another destination in the filesystem, one +should create a live snapshot in the desired destination, then stream +into that image. Example: + +(qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img qcow2 + +(qemu) block_stream ide0-hd0 + +