kubevirt-csi depends on the deprecated HotplugVolumes gate for VMI-level detach #4032

What this tracks

KubeVirt v1.9.0 marks the HotplugVolumes feature gate Deprecated ("replaced by DeclarativeHotplugVolumes"). The platform keeps it enabled on purpose (#4015), because kubevirt-csi detaches tenant volumes through the VMI-level removevolume subresource, and virt-api accepts that call on a VM-owned VMI only while HotplugVolumes is on: vmiVolumePatch checks ephemeralHotplugSupported(), which is exactly HotplugVolumesEnabled() (pkg/virt-api/rest/volumes.go). Our wrapper calls RemoveVolumeFromVMI at packages/apps/kubernetes/images/kubevirt-csi-driver/controller.go:455, and upstream kubevirt/csi-driver has the same fallback in removeVolumeFromVm for the case where the VM is already gone during teardown.

Upstream names no removal release. Its Deprecated state says "discontinued in the following release" in a doc comment, but MultiArchitecture and DisableMDEVConfiguration have been deprecated since 1.8.0 and are still registered at 1.9.0, so the state is a direction, not a date. When HotplugVolumes does become Discontinued, the VMI-level detach path stops working and tenant volume detach breaks during control-plane teardown.

While the gate stays enabled it also keeps DeclarativeHotplugVolumes inert: handleDeclarativeVolumeHotplug in pkg/virt-controller/watch/vm/vm.go returns early when HotplugVolumesEnabled(). So anything that wants declarative hotplug (dataVolume.hotpluggable: true in a VM spec) waits on the same change.

What has to happen before the gate can go

Move kubevirt-csi off the VMI-level removevolume: detach through the VM subresource while the VM exists, and for the teardown race handle the orphaned hotplug attachment pod without the VMI subresource (delete the attachment pod, or wait for the VMI to finish terminating). Then drop HotplugVolumes from the static featureGates in packages/system/kubevirt/templates/kubevirt-cr.yaml, which also switches declarative hotplug on.

Check the pinned release's pkg/virt-config/featuregate/inactive.go at every KubeVirt bump for the state of this gate.