Annotation of qemu/docs/live-block-ops.txt, revision 18.104.22.168
1.1 root 1: LIVE BLOCK OPERATIONS
4: High level description of live block operations. Note these are not
5: supported for use with the raw format at the moment.
7: Snapshot live merge
10: Given a snapshot chain, described in this document in the following
13: [A] -> [B] -> [C] -> [D]
15: Where the rightmost object ([D] in the example) described is the current
16: image which the guest OS has write access to. To the left of it is its base
17: image, and so on accordingly until the leftmost image, which has no
20: The snapshot live merge operation transforms such a chain into a
21: smaller one with fewer elements, such as this transformation relative
22: to the first example:
24: [A] -> [D]
26: Currently only forward merge with target being the active image is
27: supported, that is, data copy is performed in the right direction with
28: destination being the rightmost image.
30: The operation is implemented in QEMU through image streaming facilities.
32: The basic idea is to execute 'block_stream virtio0' while the guest is
33: running. Progress can be monitored using 'info block-jobs'. When the
34: streaming operation completes it raises a QMP event. 'block_stream'
35: copies data from the backing file(s) into the active image. When finished,
36: it adjusts the backing file pointer.
38: The 'base' parameter specifies an image which data need not be streamed from.
39: This image will be used as the backing file for the active image when the
40: operation is finished.
42: In the example above, the command would be:
44: (qemu) block_stream virtio0 A
47: Live block copy
50: To copy an in use image to another destination in the filesystem, one
51: should create a live snapshot in the desired destination, then stream
52: into that image. Example:
54: (qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img qcow2
56: (qemu) block_stream ide0-hd0