[v5,14/15] docs: describe live block operations

Submitted by Stefan Hajnoczi on Jan. 13, 2012, 1:14 p.m.


Message ID 1326460457-19446-15-git-send-email-stefanha@linux.vnet.ibm.com
State New
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Commit Message

Stefan Hajnoczi Jan. 13, 2012, 1:14 p.m.
From: Marcelo Tosatti <mtosatti@redhat.com>

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
 docs/live-block-ops.txt |   58 +++++++++++++++++++++++++++++++++++++++++++++++
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+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
+[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
+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