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Description:
[incremental_backup] Cannot delete checkpoint(bitmap) if it's in the backing file of a disk chain

Reproduced Versions:
libvirt-7.0.0-6.el9.x86_64
qemu-kvm-5.2.0-16.el9.x86_64

NOT REPRODUCED VERSIONS:
libvirt-7.0.0-13.module+el8.4.0+10604+5608c2b4.x86_64
qemu-kvm-5.2.0-15.module+el8.4.0+10650+50781ca0.x86_64

Reproducibility:
100%

Steps:
1. start a vm
(.libvirt-ci-venv-ci-runtest-vUJ1lU) [root@dell-per740-38 ~]# virsh start avocado-vt-vm1
Domain 'avocado-vt-vm1' started

2. create checkpoint for the vm
(.libvirt-ci-venv-ci-runtest-vUJ1lU) [root@dell-per740-38 ~]# virsh checkpoint-create-as avocado-vt-vm1 ck1
Domain checkpoint ck1 created

3. create a diskonly snapshot
(.libvirt-ci-venv-ci-runtest-vUJ1lU) [root@dell-per740-38 ~]# virsh snapshot-create-as avocado-vt-vm1 sp1 --disk-only
Domain snapshot sp1 created

4. delete the checkpoint created in step 2
(.libvirt-ci-venv-ci-runtest-vUJ1lU) [root@dell-per740-38 ~]# virsh checkpoint-delete avocado-vt-vm1 ck1
error: Failed to delete checkpoint ck1
error: internal error: unable to execute QEMU command 'transaction': Bitmap 'ck1' is readonly and cannot be modified

Did you enable incremental backup support via the qemu namespace element?

(In reply to Peter Krempa from comment #2)
> Did you enable incremental backup support via the qemu namespace element?

Yes, vm's xml edited as follow:
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
...
  <qemu:capabilities>
    <qemu:add capability='incremental-backup'/>
  </qemu:capabilities>
</domain>

Backups are not enabled and require qemu support for blockdev-reopen. Closing this as duplicate of the original bug report.

*** This bug has been marked as a duplicate of bug 1953939 ***