In what scenarios is vm.Snapshot.CurrentSnapshot nil?

[atc0005]

The documentation for the field notes:

Current snapshot of the virtual machine

This property is set by calling Snapshot.revert or VirtualMachine.createSnapshot. This property will be empty when the working snapshot is at the root of the snapshot tree.

Refers instance of VirtualMachineSnapshot.

I don't fully understand what "root of the snapshot tree" means. I initially assumed this meant when someone selected the first snapshot in a list and opted to revert to that snapshot or immediately after the first snapshot was created, but I'd assume that the "current snapshot" would be either of those cases: the one you reverted to or the first snapshot created.

In short, I'm attempting to both understand the explicit meaning of that field and determine whether it should always be set when a snapshot is present for a virtual machine.

I found this simulator code which indicates that when both vm.Snapshot and vm.Snapshot.CurrentSnapshot are non-nil then snapshots are present:

govmomi/simulator/virtual_machine.go

Lines 1942 to 1946 in 55b758a

	assertNoSnapshots := func(allowSingleChain bool) types.BaseMethodFault {
	hasSnapshots := vm.Snapshot != nil && vm.Snapshot.CurrentSnapshot != nil
	if !hasSnapshots {
	return nil
	}

Is this reliable?

[atc0005]

Google search for:

when would govmomi VirtualMachineSnapshotInfo CurrentSnapshot field be nil

returns this via Google Gemini:

The CurrentSnapshot field in govmomi's VirtualMachineSnapshotInfo will be nil (or effectively absent/null) when the virtual machine has no snapshots taken, as it only populates when a snapshot chain exists, indicating the active snapshot within that chain; if the VM has never been snapshotted, there's no current snapshot to point to, hence the nil value.

This seems to line up with the idea that when snapshots are being consolidated that there are snapshots, but none are current.

Using the "Dive deeper in AI Mode" option yields:

In the govmomi library (and the underlying vSphere API), the CurrentSnapshot field within the VirtualMachineSnapshotInfo structure is nil in the following scenarios:

• No Snapshots Exist: The most common reason is that the Virtual Machine has no snapshots. If the RootSnapshotList is empty, there is no "current" point in the snapshot tree to reference.
• Virtual Machine is "Live" (at the tip): If you are running on the current state of the VM and it is not specifically "reverted" to or residing on a historical snapshot, the system may not populate this field if the current execution point isn't explicitly tied to a snapshot leaf.
• Recent Snapshot Deletion: If all snapshots have been deleted or the specific current snapshot was just removed/consolidated, the field will be cleared once the task completes.
• Property Not Populated: If you are using a PropertyCollector or mo.VirtualMachine and did not explicitly include the snapshot property in your SelectSet, the entire Snapshot structure (including CurrentSnapshot) will be nil in your local object.

To verify your VM's snapshot status, you can use the govc snapshot.tree command to see a visual representation of the tree and current marker.

If you're writing code, ensure you collect the snapshot property explicitly in your PropertyCollector call to avoid getting a nil result due to missing data.

A different search for govmomi VirtualMachineSnapshotInfo CurrentSnapshot field be nil yields:

Yes, govmomi.types.VirtualMachineSnapshotInfo.CurrentSnapshot can be nil (or null in JSON/SOAP), which indicates the virtual machine currently has no active snapshots, meaning it's running directly from its base disk or a consolidated chain, not from a specific snapshot state. You must handle this nil case in your Go code, checking if vm.Snapshot == nil || vm.Snapshot.CurrentSnapshot == nil before trying to access snapshot details, especially when dealing with VM power states or snapshot management operations.

Why it happens:

• No Snapshot Taken: The VM was powered on and has never had a snapshot created.
• All Snapshots Deleted: All existing snapshots have been fully merged back into the base disk.
• During Snapshot Operations: Before a snapshot is fully created or after it's completely deleted/consolidated, CurrentSnapshot might be temporarily absent or nil.

Example code provided by Google Gemini for dealing with the scenario:

import (
	"context"
	"fmt"
	"log"

	"github.com/vmware/govmomi/object"
	"github.com/vmware/govmomi/vim25/mo"
)

// Assuming 'vm' is a *mo.VirtualMachine object obtained via govmomi
// and 'ctx' is a context.Context

func checkSnapshot(ctx context.Context, vm *mo.VirtualMachine) {
	if vm.Snapshot == nil || vm.Snapshot.CurrentSnapshot == nil {
		log.Printf("VM '%s' has no current active snapshot.", vm.Name)
	} else {
		log.Printf("VM '%s' current snapshot: %s (ID: %s)",
			vm.Name,
			vm.Snapshot.CurrentSnapshot.Name,
			vm.Snapshot.CurrentSnapshot.Id,
		)
		// You can also access other snapshot info if needed:
		// log.Printf("Snapshot list count: %d", len(vm.Snapshot.ChildSnapshotList))
	}
}

// Example usage (conceptual):
// vm := object.NewVirtualMachine(c, vmRef)
// var vmo mo.VirtualMachine
// err := vm.Properties(ctx, vmRef, []string{"snapshot"}, &vmo)
// if err != nil { log.Fatal(err) }
// checkSnapshot(ctx, &vmo)

and with closing comments:

By checking for nil first, your code remains robust and avoids panics when a VM isn't in a snapshot state, allowing you to correctly manage or report on its snapshot status.

Ultimately, I think this is the relevant bit:

During Snapshot Operations: Before a snapshot is fully created or after it's completely deleted/consolidated, CurrentSnapshot might be temporarily absent or nil.

Do I have the correct understanding?