Allow external snapshots because internal snapshots of UEFI VMs are not supported

[OpenNebulaSupport]

Description Currently opennebula does not allow UEFI VM snapshots. The snapshots being done right now are internal and they are not supported by libvirt.

To Reproduce When a snapshot of a UEFI VM is made, the following error appears

[VMM][I]: error: Operation not supported: internal snapshots of a VM with pflash based firmware are not supported

This should not be happening in datastores with external snapshot logic

Expected behavior

• A snapshot should be created and it should be easy to be reverted

Details

• Affected Component: Snapshots
• Hypervisor: KVM
• Version: 6.8

Additional context If the VM is UEFI, in src/vmm_mad/remotes/kvm/snapshot_create :

• dynamic_ownership = 1 has to be set in /etc/libvirt/qemu.conf
• external snapshots (snapshot-create-as) should be called with --disk-only

After that, reverting the snapshot is more complicated because the snap has to be deleted and the VM has to go back to the previous image. Using qemu-img directly could be a better approach

Progress Status

• [ ] Code committed
• [ ] Testing - QA
• [ ] Documentation (Release notes - resolved issues, compatibility, known issues)

[atodorov-storpool]

I am trying to remember where we discussed this, but I believe the UEFI NVRAM (pflash) should be managed and handled by the SYSTEM datastore TM_MAD as volatile storage. Also, IMO, disk-only snapshots should be handled by the SYSTEM TM_MAD, although the responsibility is a bit blurry.

[jzvikart]

+1. UEFI is de-facto standard and this is essentially making snapshots useless.

[rsmontero]

Check support for revert added in this libvirt version https://libvirt.org/news.html#v9-9-0-2023-11-01