From mboxrd@z Thu Jan 1 00:00:00 1970 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 Message-Id: <20120104140945.802506060@redhat.com> Date: Wed, 04 Jan 2012 12:08:58 -0200 From: Marcelo Tosatti References: <20120104140854.631720304@redhat.com> Content-Disposition: inline; filename=live-block-operations Subject: [Qemu-devel] [patch 4/4] add doc to describe live block operations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: stefanha@linux.vnet.ibm.com, kwolf@redhat.com, qemu-devel@nongnu.org Cc: Marcelo Tosatti 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 + +