[libvirt] [PATCH v8 03/21] backup: Introduce virDomainCheckpoint APIs

[Peter Krempa]

On Wed, Apr 17, 2019 at 09:09:03 -0500, Eric Blake wrote:
> Introduce a bunch of new public APIs related to backup checkpoints.
> Checkpoints are modeled heavily after virDomainSnapshotPtr (both
> represent a point in time of the guest), although a snapshot exists
> with the intent of rolling back to that state, while a checkpoint
> exists to make it possible to create an incremental backup at a later
> time.
> 
> The following map shows the API relations to snapshots, with new APIs
> on the right:
> 
> Operate on a domain object to create/redefine a child:
> virDomainSnapshotCreateXML          virDomainCheckpointCreateXML
> 
> Operate on a child object for lifetime management:
> virDomainSnapshotDelete             virDomainCheckpointDelete
> virDomainSnapshotFree               virDomainCheckpointFree
> virDomainSnapshotRef                virDomainCheckpointRef
> 
> Operate on a child object to learn more about it:
> virDomainSnapshotGetXMLDesc         virDomainCheckpointGetXMLDesc
> virDomainSnapshotGetConnect         virDomainCheckpointGetConnect
> virDomainSnapshotGetDomain          virDomainCheckpointGetDomain
> virDomainSnapshotGetName            virDomainCheckpiontGetName
> virDomainSnapshotGetParent          virDomainCheckpiontGetParent
> virDomainSnapshotHasMetadata        virDomainCheckpointHasMetadata
> virDomainSnapshotIsCurrent          virDomainCheckpointIsCurrent

The 'current' checkpoint has very sparse documentation. While it makes
some sense for the current snapshot to exist I'm not persuaded we need
this for checkpoints.

In case of checkpoints the bitmaps backing it track the state even if
you create a new bitmap unlike checkpoints. Thus it does not seem to
make sense to me.

If you think it does please elaborate, ideally in form of documentation.

> Operate on a domain object to list all children:
> virDomainSnapshotNum                (no counterpart, this is the old
> virDomainSnapshotListNames           racy interface)
> virDomainSnapshotListAllSnapshots   virDomainListAllCheckpoints
> 
> Operate on a child object to list descendents:
> virDomainSnapshotNumChildren        (no counterpart, this is the old
> virDomainSnapshotListChildrenNames   racy interface)
> virDomainSnapshotListAllChildren    virDomainCheckpointListAllChildren
> 
> Operate on a domain to locate a particular child:
> virDomainSnapshotLookupByName       virDomainCheckpointLookupByName
> virDomainHasCurrentSnapshot         virDomainHasCurrentCheckpoint
> virDomainSnapshotCurrent            virDomainCheckpointCurrent
> 
> Operate on a snapshot to roll back to earlier state:
> virDomainSnapshotRevert             (no counterpart, instead checkpoints
>                                      are used in incremental backups via

This patch or a different one should also add docs to virDomainSnapshotRevert
that outline what happens to the checkpoints when reverting snapshots.

Basically what should happen is that an alternate reality should
probably be created as the disk images can change at that point


> 				     XML to virDomainBackupBegin)
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>
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