Add ImageVolumeSource API

Adding the required Kubernetes API so that the kubelet can start using
it. This patch also adds the corresponding alpha feature gate as
outlined in KEP 4639.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

pkg/api/pod/util.go

@@ -385,6 +385,7 @@ func GetValidationOptionsFromPodSpecAndMeta(podSpec, oldPodSpec *api.PodSpec, po
 		AllowInvalidTopologySpreadConstraintLabelSelector: false,
 		AllowNamespacedSysctlsForHostNetAndHostIPC:        false,
 		AllowNonLocalProjectedTokenPath:                   false,
+		AllowImageVolumeSource:                            utilfeature.DefaultFeatureGate.Enabled(features.ImageVolume),
 	}
 
 	// If old spec uses relaxed validation or enabled the RelaxedEnvironmentVariableValidation feature gate,
@@ -713,6 +714,7 @@ func dropDisabledFields(
 	}
 
 	dropPodLifecycleSleepAction(podSpec, oldPodSpec)
+	dropImageVolumes(podSpec, oldPodSpec)
 }
 
 func dropPodLifecycleSleepAction(podSpec, oldPodSpec *api.PodSpec) {
@@ -1260,3 +1262,56 @@ func MarkPodProposedForResize(oldPod, newPod *api.Pod) {
 		}
 	}
 }
+
+// KEP: https://kep.k8s.io/4639
+func dropImageVolumes(podSpec, oldPodSpec *api.PodSpec) {
+	if utilfeature.DefaultFeatureGate.Enabled(features.ImageVolume) || imageVolumesInUse(oldPodSpec) {
+		return
+	}
+
+	imageVolumeNames := sets.New[string]()
+	var newVolumes []api.Volume
+	for _, v := range podSpec.Volumes {
+		if v.Image != nil {
+			imageVolumeNames.Insert(v.Name)
+			continue
+		}
+		newVolumes = append(newVolumes, v)
+	}
+	podSpec.Volumes = newVolumes
+
+	dropVolumeMounts := func(givenMounts []api.VolumeMount) (newVolumeMounts []api.VolumeMount) {
+		for _, m := range givenMounts {
+			if !imageVolumeNames.Has(m.Name) {
+				newVolumeMounts = append(newVolumeMounts, m)
+			}
+		}
+		return newVolumeMounts
+	}
+
+	for i, c := range podSpec.Containers {
+		podSpec.Containers[i].VolumeMounts = dropVolumeMounts(c.VolumeMounts)
+	}
+
+	for i, c := range podSpec.InitContainers {
+		podSpec.InitContainers[i].VolumeMounts = dropVolumeMounts(c.VolumeMounts)
+	}
+
+	for i, c := range podSpec.EphemeralContainers {
+		podSpec.EphemeralContainers[i].VolumeMounts = dropVolumeMounts(c.VolumeMounts)
+	}
+}
+
+func imageVolumesInUse(podSpec *api.PodSpec) bool {
+	if podSpec == nil {
+		return false
+	}
+
+	for _, v := range podSpec.Volumes {
+		if v.Image != nil {
+			return true
+		}
+	}
+
+	return false
+}