How to merge incremental backups generated with virsh backup-begin?

[Jorge Luiz Correa]

I'm trying to create incremental backups that I could restore when
necessary. All backups are being generated fine but I couldn't find a way
to recreate an image using all or some of the backup files.

For example, my domain is called jammy and is running.

jammy-backup.xml:
<domainbackup>
  <incremental></incremental>
</domainbackup>

jammy-checkpoint.xml
<domaincheckpoint>
  <disks>
    <disk name="vda" checkpoint="bitmap"/>
  </disks>
</domaincheckpoint>

~# virsh backup-begin jammy jammy-backup.xml jammy-checkpoint.xml

* This command with these files generates backup file in
/var/lib/libvirt/images appending the checkpoint timestamp in file name
(jammy.qcow2 -> jammy.qcow2.TIMESTAMP).

~# virsh checkpoint-list jammy
 Name         Creation Time
-----------------------------------------
 1666006874   2022-10-17 08:41:14 -0300

~# ls -lh /var/lib/libvirt/images
-rw-r--r-- 1 libvirt-qemu kvm  2,6G out 18 14:38 jammy.qcow2
-rw------- 1 root root         1,5G out 17 08:41 jammy.qcow2.1666006874

If I create a new domain using jammy.qcow2.1666006874 as disk, everything
works good.

Then, I've created some incremental backups.

jammy-backup.xml:
<domainbackup>
  <incremental>1666006874</incremental>
</domainbackup>

~# virsh backup-begin jammy jammy-backup.xml jammy-checkpoint.xml

~# ls -lh /var/lib/libvirt/images
-rw-r--r-- 1 libvirt-qemu kvm  2,6G out 18 14:38 jammy.qcow2
-rw------- 1 root root         1,5G out 17 08:41 jammy.qcow2.1666006874
-rw------- 1 root root         247M out 17 14:42 jammy.qcow2.1666010735

At this point, if I need to restore the backup with checkpoint 1666010735,
how can I create a new image using jammy.qcow2.1666010735 and
jammy.qcow2.1666006874?

I would like to merge the incremental backup jammy.qcow2.1666010735 into
the full backup jammy.qcow2.1666006874, to get a new image so I can create
a new domain using it as disk. Am I doing it the right way?

Ubuntu 22.04 LTS
KVM
libvirt 8.0.0-1ubuntu7.1
qemu 1:6.2+dfsg-2ubuntu6.4

Thank you!

-- 
Jorge Luiz Corrêa
Embrapa Agricultura Digital

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