KVM NAS backup: resume VM and exit on backup failure

Fix three bugs in nasbackup.sh that caused VMs to remain paused
indefinitely when backup jobs fail (e.g. storage full):

1. Add exit after cleanup on Failed backup job status to prevent
   infinite polling loop in backup_running_vm()
2. Add exit after cleanup on qemu-img convert failure in
   backup_stopped_vm() to stop processing subsequent disks
3. Add VM state check and virsh resume to cleanup() so paused VMs
   are automatically resumed after backup failure

Fixes apache#12821

Author: jmsperu

scripts/vm/hypervisor/kvm/nasbackup.sh

@@ -141,7 +141,8 @@ backup_running_vm() {
         break ;;
       Failed)
         echo "Virsh backup job failed"
-        cleanup ;;
+        cleanup
+        exit 1 ;;
     esac
     sleep 5
   done
@@ -177,6 +178,7 @@ backup_stopped_vm() {
     if ! qemu-img convert -O qcow2 "$disk" "$output" > "$logFile" 2> >(cat >&2); then
       echo "qemu-img convert failed for $disk $output"
       cleanup
+      exit 1
     fi
     name="datadisk"
   done
@@ -221,6 +223,20 @@ mount_operation() {
 cleanup() {
   local status=0
 
+  # Resume the VM if it was paused (e.g. by virsh backup-begin)
+  if [[ -n "$VM" ]]; then
+    local vm_state
+    vm_state=$(virsh -c qemu:///system domstate "$VM" 2>/dev/null)
+    if [[ "$vm_state" == "paused" ]]; then
+      if virsh -c qemu:///system resume "$VM" > /dev/null 2>&1; then
+        log -ne "Resumed VM $VM after backup failure"
+      else
+        echo "Failed to resume VM $VM - manual intervention required (virsh resume $VM)"
+        status=1
+      fi
+    fi
+  fi
+
   rm -rf "$dest" || { echo "Failed to delete $dest"; status=1; }
   umount "$mount_point" || { echo "Failed to unmount $mount_point"; status=1; }
   rmdir "$mount_point" || { echo "Failed to remove mount point $mount_point"; status=1; }