1029641bef
Signed-off-by: Alberto Garcia <berto@igalia.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
73 lines
2.3 KiB
Plaintext
73 lines
2.3 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.
|
|
|
|
Note also that this document is incomplete and it currently only
|
|
covers the 'stream' operation. Other operations supported by QEMU such
|
|
as 'commit', 'mirror' and 'backup' are not described here yet. Please
|
|
refer to the qapi/block-core.json file for an overview of those.
|
|
|
|
Snapshot live merge
|
|
===================
|
|
|
|
Given a snapshot chain, described in this document in the following
|
|
format:
|
|
|
|
[A] <- [B] <- [C] <- [D] <- [E]
|
|
|
|
Where the rightmost object ([E] 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] <- [E]
|
|
|
|
Data is copied in the right direction with destination being the
|
|
rightmost image, but any other intermediate image can be specified
|
|
instead. In this example data is copied from [C] into [D], so [D] can
|
|
be backed by [B]:
|
|
|
|
[A] <- [B] <- [D] <- [E]
|
|
|
|
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
|
|
destination image when the operation is finished.
|
|
|
|
In the first example above, the command would be:
|
|
|
|
(qemu) block_stream virtio0 file-A.img
|
|
|
|
In order to specify a destination image different from the active
|
|
(rightmost) one we can use its node name instead.
|
|
|
|
In the second example above, the command would be:
|
|
|
|
(qemu) block_stream node-D file-B.img
|
|
|
|
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
|
|
|
|
|