daemonset: Simplify the logic for calculating unavailable pods

In order to maintain the correct invariants, the existing maxUnavailable
logic calculated the same data several times in different ways. Leverage
the simpler structure from maxSurge and calculate pod availability only
once, as well as perform only a single pass over all the pods in the
daemonset. This changed no behavior of the current controller, and
has a structure that is almost identical to maxSurge.

pkg/controller/daemon/util/daemonset_util.go

@@ -19,7 +19,6 @@ package util
 import (
 	"fmt"
 	"strconv"
-	"time"
 
 	apps "k8s.io/api/apps/v1"
 	v1 "k8s.io/api/core/v1"
@@ -27,7 +26,6 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	intstrutil "k8s.io/apimachinery/pkg/util/intstr"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
-	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
 	v1helper "k8s.io/kubernetes/pkg/apis/core/v1/helper"
 	"k8s.io/kubernetes/pkg/features"
 )
@@ -172,20 +170,6 @@ func IsPodUpdated(pod *v1.Pod, hash string, dsTemplateGeneration *int64) bool {
 	return hashMatches || templateMatches
 }
 
-// SplitByAvailablePods splits provided daemon set pods by availability.
-func SplitByAvailablePods(minReadySeconds int32, pods []*v1.Pod, now time.Time) ([]*v1.Pod, []*v1.Pod) {
-	availablePods := make([]*v1.Pod, 0, len(pods))
-	var unavailablePods []*v1.Pod
-	for _, pod := range pods {
-		if podutil.IsPodAvailable(pod, minReadySeconds, metav1.Time{Time: now}) {
-			availablePods = append(availablePods, pod)
-		} else {
-			unavailablePods = append(unavailablePods, pod)
-		}
-	}
-	return availablePods, unavailablePods
-}
-
 // ReplaceDaemonSetPodNodeNameNodeAffinity replaces the RequiredDuringSchedulingIgnoredDuringExecution
 // NodeAffinity of the given affinity with a new NodeAffinity that selects the given nodeName.
 // Note that this function assumes that no NodeAffinity conflicts with the selected nodeName.