[KVM] Restored backup volume not attached to running VM via libvirt - only database updated

[furkandogmus]

problem

Description

When restoring a volume from backup and attaching it to a running KVM VM, the volume is only attached at the database level but not actually hot-attached to the running VM via libvirt. This means:

1. The volume appears in CloudStack UI as "attached"
2. The volume does NOT appear in virsh domblklist <vm-name>
3. The volume is NOT visible inside the guest OS
4. User must reboot(forced) the VM to see the restored volume

Root Cause

In KVMGuru.attachRestoredVolumeToVirtualMachine() (line 380-400), the method only:

• Updates the volume state in the database via _volumeDao.attachVolume()
• Sets volume state to Ready
  It does NOT:
• Check if VM is running
• Send an AttachCommand to the KVM agent to hot-attach the disk via libvirt

Expected Behavior

When attaching a restored volume to a running VM:

1. CloudStack should detect the VM state
2. If VM is Running, send a libvirt attach command to hot-attach the disk
3. Volume should immediately appear in virsh domblklist and inside guest OS
4. No reboot should be required

versions

CloudStack: 4.21.0
Hypervisor: KVM
Host OS: Rocky Linux 9
Guest OS: Rocky Linux 9 / Windows 10 - 2022 Server

The steps to reproduce the bug

Steps to Reproduce

1. Create a VM with a data disk
2. Create a backup of the VM
3. Start the VM (ensure it's running)
4. Restore the backed-up volume and attach to the running VM via API:
   restoreVolumeFromBackupAndAttachToVM
5. Check virsh domblklist <vm-name> on the KVM host
6. Observe: The restored volume is NOT listed
7. Check inside guest OS
8. Observe: The disk is NOT visible
9. Reboot(forced) the VM
10. Observe: After reboot(forced), the disk appears

What to do about it?

Either:
A) Add hot-attach logic to KVMGuru.attachRestoredVolumeToVirtualMachine() to send AttachCommand when VM is running
B) Or document this as expected behavior and require users to stop VM before restoring volumes
Option A is preferred as it aligns with how regular attachVolume API works for running VMs.