mirror of
https://github.com/xemu-project/xemu.git
synced 2024-11-30 15:00:34 +00:00
59 lines
1.8 KiB
Plaintext
59 lines
1.8 KiB
Plaintext
|
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
|
||
|
|
|
||
|
|
|