From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:60540) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RqSIC-0000Tt-24 for qemu-devel@nongnu.org; Thu, 26 Jan 2012 11:35:25 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RqSI6-0003T7-Oc for qemu-devel@nongnu.org; Thu, 26 Jan 2012 11:35:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43745) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RqSI5-0003Sl-Lj for qemu-devel@nongnu.org; Thu, 26 Jan 2012 11:35:14 -0500 From: Kevin Wolf Date: Thu, 26 Jan 2012 17:38:11 +0100 Message-Id: <1327595896-19623-18-git-send-email-kwolf@redhat.com> In-Reply-To: <1327595896-19623-1-git-send-email-kwolf@redhat.com> References: <1327595896-19623-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 17/22] docs: describe live block operations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Marcelo Tosatti Signed-off-by: Marcelo Tosatti Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- docs/live-block-ops.txt | 58 +++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 58 insertions(+), 0 deletions(-) create mode 100644 docs/live-block-ops.txt diff --git a/docs/live-block-ops.txt b/docs/live-block-ops.txt new file mode 100644 index 0000000..a257087 --- /dev/null +++ b/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 + + -- 1.7.6.5