Merge pull request #55665 from brendandburns/path

Automatic merge from submit-queue (batch tested with PRs 55908, 55829, 55293, 55653, 55665). 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>.

If mountPath is missing, prefix with root dir.

If `mountPath` is not absolute, add the os-specific root directory as a prefix.

Ref: https://github.com/kubernetes/kubernetes/pull/51240
https://groups.google.com/forum/#!topic/kubernetes-sig-storage/k_0Wr2kYkpU

@thockin @saad-ali @andyzhangx 

Note to @thockin I left the validation in place, in seems like it is a net win, since it will give a decent
error message to most people, but the fall-back defaulting is there if it doesn't catch 'c:'

I'm happy to rip out the validation if that is preferable to everyone.  Let me know.

```release-note
If a non-absolute mountPath is passed to the kubelet, prefix it with the appropriate root path.
```

pkg/apis/core/types.go

@@ -1530,7 +1530,9 @@ type VolumeMount struct {
 	// Optional: Defaults to false (read-write).
 	// +optional
 	ReadOnly bool
-	// Required. Must not contain ':'.
+	// Required. If the path is not an absolute path (e.g. some/path) it
+	// will be prepended with the appropriate root prefix for the operating
+	// system.  On Linux this is '/', on Windows this is 'C:\'.
 	MountPath string
 	// Path within the volume from which the container's volume should be mounted.
 	// Defaults to "" (volume's root).

pkg/apis/core/validation/validation.go

@@ -1965,13 +1965,6 @@ func ValidateVolumeMounts(mounts []core.VolumeMount, volumes sets.String, contai
 		if mountpoints.Has(mnt.MountPath) {
 			allErrs = append(allErrs, field.Invalid(idxPath.Child("mountPath"), mnt.MountPath, "must be unique"))
 		}
-		if !path.IsAbs(mnt.MountPath) {
-			// also allow windows absolute path
-			p := mnt.MountPath
-			if len(p) < 2 || ((p[0] < 'A' || p[0] > 'Z') && (p[0] < 'a' || p[0] > 'z')) || p[1] != ':' {
-				allErrs = append(allErrs, field.Invalid(idxPath.Child("mountPath"), mnt.MountPath, "must be an absolute path"))
-			}
-		}
 		mountpoints.Insert(mnt.MountPath)
 		if len(mnt.SubPath) > 0 {
 			allErrs = append(allErrs, validateLocalDescendingPath(mnt.SubPath, fldPath.Child("subPath"))...)

pkg/apis/core/validation/validation_test.go

@@ -3849,10 +3849,8 @@ func TestValidateVolumeMounts(t *testing.T) {
 		"empty name":                             {{Name: "", MountPath: "/foo"}},
 		"name not found":                         {{Name: "", MountPath: "/foo"}},
 		"empty mountpath":                        {{Name: "abc", MountPath: ""}},
-		"relative mountpath":                     {{Name: "abc", MountPath: "bar"}},
 		"mountpath collision":                    {{Name: "foo", MountPath: "/path/a"}, {Name: "bar", MountPath: "/path/a"}},
 		"absolute subpath":                       {{Name: "abc", MountPath: "/bar", SubPath: "/baz"}},
-		"windows absolute subpath":               {{Name: "abc", MountPath: "D", SubPath: ""}},
 		"subpath in ..":                          {{Name: "abc", MountPath: "/bar", SubPath: "../baz"}},
 		"subpath contains ..":                    {{Name: "abc", MountPath: "/bar", SubPath: "baz/../bat"}},
 		"subpath ends in ..":                     {{Name: "abc", MountPath: "/bar", SubPath: "./.."}},