Merge pull request #65837 from clandry94/pvc_describe_claimed_by

Automatic merge from submit-queue (batch tested with PRs 65838, 65837). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

output which pods are a pvc in use when kubectl describe pvc is run

**What this PR does / why we need it**:
This PR implements a feature request to display the pods mounted to a PVC when `kubectl describe pvc` is ran. We need it since the only way to see which pods are bound to a PVC is by checking the volume mounts of each individual pod in the namespace. 

Example Output:
```
$ kubectl get pods,pvc
NAME     READY  STATUS    RESTARTS   AGE
test-pod   1/1       Running       0                2h

NAME      STATUS    VOLUME                                   CAPACITY  ACCESS MODES   STORAGECLASS        AGE
test-pvc  Bound     pvc-718681dd-70cc-11e7-aa14-42010af00029   100Gi      RWO            us-east1-b          345d
```

```
$ kubectl describe pvc
Name:          elasticsearch-data-elasticsearch-data-us-east1-b-0
Namespace:     partners-production
StorageClass:  us-east1-b
Status:        Bound
Volume:      pvc-718681dd-70cc-11e7-aa14-42010af00029
Labels:       <none>
Annotations:   <none>
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      1Gi
Access Modes:  RWO
Events:        <none>
Mounted By:     test-pod
```

Pods using the PVC are shown with the `Mounted By` field

**Which issue(s) this PR fixes**:
Closes #65233 

**Special notes for your reviewer**:

**Release note**:
```release-note
Running `kubectl describe pvc` now shows which pods are mounted to the pvc being described with the `Mounted By` field
```

pkg/printers/internalversion/describe.go

@@ -1291,12 +1291,52 @@ func (d *PersistentVolumeClaimDescriber) Describe(namespace, name string, descri
 		return "", err
 	}
 
+	pc := d.Core().Pods(namespace)
+
+	mountPods, err := getMountPods(pc, pvc.Name)
+	if err != nil {
+		return "", err
+	}
+
 	events, _ := d.Core().Events(namespace).Search(legacyscheme.Scheme, pvc)
 
-	return describePersistentVolumeClaim(pvc, events)
+	return describePersistentVolumeClaim(pvc, events, mountPods)
 }
 
-func describePersistentVolumeClaim(pvc *api.PersistentVolumeClaim, events *api.EventList) (string, error) {
+func getMountPods(c coreclient.PodInterface, pvcName string) ([]api.Pod, error) {
+	nsPods, err := c.List(metav1.ListOptions{})
+	if err != nil {
+		return []api.Pod{}, err
+	}
+
+	var pods []api.Pod
+
+	for _, pod := range nsPods.Items {
+		pvcs := getPvcs(pod.Spec.Volumes)
+
+		for _, pvc := range pvcs {
+			if pvc.PersistentVolumeClaim.ClaimName == pvcName {
+				pods = append(pods, pod)
+			}
+		}
+	}
+
+	return pods, nil
+}
+
+func getPvcs(volumes []api.Volume) []api.Volume {
+	var pvcs []api.Volume
+
+	for _, volume := range volumes {
+		if volume.VolumeSource.PersistentVolumeClaim != nil {
+			pvcs = append(pvcs, volume)
+		}
+	}
+
+	return pvcs
+}
+
+func describePersistentVolumeClaim(pvc *api.PersistentVolumeClaim, events *api.EventList, mountPods []api.Pod) (string, error) {
 	return tabbedString(func(out io.Writer) error {
 		w := NewPrefixWriter(out)
 		w.Write(LEVEL_0, "Name:\t%s\n", pvc.Name)
@@ -1342,6 +1382,8 @@ func describePersistentVolumeClaim(pvc *api.PersistentVolumeClaim, events *api.E
 			DescribeEvents(events, w)
 		}
 
+		printPodsMultiline(w, "Mounted By", mountPods)
+
 		return nil
 	})
 }
@@ -3867,6 +3909,37 @@ func printTaintsMultilineWithIndent(w PrefixWriter, initialIndent, title, innerI
 	}
 }
 
+// printPodsMultiline prints multiple pods with a proper alignment.
+func printPodsMultiline(w PrefixWriter, title string, pods []api.Pod) {
+	printPodsMultilineWithIndent(w, "", title, "\t", pods)
+}
+
+// printPodsMultilineWithIndent prints multiple pods with a user-defined alignment.
+func printPodsMultilineWithIndent(w PrefixWriter, initialIndent, title, innerIndent string, pods []api.Pod) {
+	w.Write(LEVEL_0, "%s%s:%s", initialIndent, title, innerIndent)
+
+	if pods == nil || len(pods) == 0 {
+		w.WriteLine("<none>")
+		return
+	}
+
+	// to print pods in the sorted order
+	sort.Slice(pods, func(i, j int) bool {
+		cmpKey := func(pod api.Pod) string {
+			return pod.Name
+		}
+		return cmpKey(pods[i]) < cmpKey(pods[j])
+	})
+
+	for i, pod := range pods {
+		if i != 0 {
+			w.Write(LEVEL_0, "%s", initialIndent)
+			w.Write(LEVEL_0, "%s", innerIndent)
+		}
+		w.Write(LEVEL_0, "%s\n", pod.Name)
+	}
+}
+
 // printPodTolerationsMultiline prints multiple tolerations with a proper alignment.
 func printPodTolerationsMultiline(w PrefixWriter, title string, tolerations []api.Toleration) {
 	printTolerationsMultilineWithIndent(w, "", title, "\t", tolerations)