deprecate CephFS plugin from available in-tree drivers.

https://groups.google.com/a/kubernetes.io/g/dev/c/g8rwL-qnQhk
based on above, the consensus was to start the deprecation in v1.28.

This commit start the deprecation process of CephFS plugin from
in-tree drivers.

Signed-off-by: Humble Chirammal <humble.devassy@gmail.com>

pkg/api/persistentvolume/util.go

@@ -79,6 +79,10 @@ func warningsForPersistentVolumeSpecAndMeta(fieldPath *field.Path, pvSpec *api.P
 			warnings = append(warnings, nodeapi.GetWarningsForNodeSelectorTerm(term, termFldPath.Index(i))...)
 		}
 	}
+	// If we are on deprecated volume plugin
+	if pvSpec.CephFS != nil {
+		warnings = append(warnings, fmt.Sprintf("%s: deprecated in v1.28, non-functional in v1.31+", fieldPath.Child("spec", "persistentVolumeSource").Child("cephfs")))
+	}
 
 	return warnings
 }

pkg/api/persistentvolume/util_test.go

@@ -176,6 +176,26 @@ func TestWarnings(t *testing.T) {
 				`spec.nodeAffinity.required.nodeSelectorTerms[0].matchExpressions[0].key: beta.kubernetes.io/os is deprecated since v1.14; use "kubernetes.io/os" instead`,
 			},
 		},
+		{
+			name: "PV CephFS deprecation warning",
+			template: &api.PersistentVolume{
+				Spec: api.PersistentVolumeSpec{
+					PersistentVolumeSource: api.PersistentVolumeSource{
+						CephFS: &api.CephFSPersistentVolumeSource{
+							Monitors:   nil,
+							Path:       "",
+							User:       "",
+							SecretFile: "",
+							SecretRef:  nil,
+							ReadOnly:   false,
+						},
+					},
+				},
+			},
+			expected: []string{
+				`spec.persistentVolumeSource.cephfs: deprecated in v1.28, non-functional in v1.31+`,
+			},
+		},
 	}
 
 	for _, tc := range testcases {

pkg/api/pod/warnings.go

@@ -160,6 +160,9 @@ func warningsForPodSpecAndMeta(fieldPath *field.Path, podSpec *api.PodSpec, meta
 		if v.Ephemeral != nil && v.Ephemeral.VolumeClaimTemplate != nil {
 			warnings = append(warnings, pvcutil.GetWarningsForPersistentVolumeClaimSpec(fieldPath.Child("spec", "volumes").Index(i).Child("ephemeral").Child("volumeClaimTemplate").Child("spec"), v.Ephemeral.VolumeClaimTemplate.Spec)...)
 		}
+		if v.CephFS != nil {
+			warnings = append(warnings, fmt.Sprintf("%s: deprecated in v1.28, non-functional in v1.31+", fieldPath.Child("spec", "volumes").Index(i).Child("cephfs")))
+		}
 	}
 
 	// duplicate hostAliases (#91670, #58477)

pkg/api/pod/warnings_test.go

@@ -214,7 +214,16 @@ func TestWarnings(t *testing.T) {
 				}},
 			},
 			expected: []string{`spec.volumes[0].glusterfs: deprecated in v1.25, non-functional in v1.26+`},
+		}, {
+			name: "CephFS",
+			template: &api.PodTemplateSpec{Spec: api.PodSpec{
+				Volumes: []api.Volume{
+					{Name: "s", VolumeSource: api.VolumeSource{CephFS: &api.CephFSVolumeSource{}}},
+				}},
+			},
+			expected: []string{`spec.volumes[0].cephfs: deprecated in v1.28, non-functional in v1.31+`},
 		},
+
 		{
 			name: "duplicate hostAlias",
 			template: &api.PodTemplateSpec{Spec: api.PodSpec{