operation_executor.go

/*
Copyright 2016 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package operationexecutor implements interfaces that enable execution of
// attach, detach, mount, and unmount operations with a
// nestedpendingoperations so that more than one operation is never triggered
// on the same volume for the same pod.
package operationexecutor

import (
	"fmt"
	"time"

	"github.com/golang/glog"

	"k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/types"
	expandcache "k8s.io/kubernetes/pkg/controller/volume/expand/cache"
	"k8s.io/kubernetes/pkg/util/mount"
	"k8s.io/kubernetes/pkg/volume"
	"k8s.io/kubernetes/pkg/volume/util"
	"k8s.io/kubernetes/pkg/volume/util/nestedpendingoperations"
	volumetypes "k8s.io/kubernetes/pkg/volume/util/types"
	"k8s.io/kubernetes/pkg/volume/util/volumepathhandler"
)

// OperationExecutor defines a set of operations for attaching, detaching,
// mounting, or unmounting a volume that are executed with a NewNestedPendingOperations which
// prevents more than one operation from being triggered on the same volume.
//
// These operations should be idempotent (for example, AttachVolume should
// still succeed if the volume is already attached to the node, etc.). However,
// they depend on the volume plugins to implement this behavior.
//
// Once an operation completes successfully, the actualStateOfWorld is updated
// to indicate the volume is attached/detached/mounted/unmounted.
//
// If the OperationExecutor fails to start the operation because, for example,
// an operation with the same UniqueVolumeName is already pending, a non-nil
// error is returned.
//
// Once the operation is started, since it is executed asynchronously,
// errors are simply logged and the goroutine is terminated without updating
// actualStateOfWorld (callers are responsible for retrying as needed).
//
// Some of these operations may result in calls to the API server; callers are
// responsible for rate limiting on errors.
type OperationExecutor interface {
	// AttachVolume attaches the volume to the node specified in volumeToAttach.
	// It then updates the actual state of the world to reflect that.
	AttachVolume(volumeToAttach VolumeToAttach, actualStateOfWorld ActualStateOfWorldAttacherUpdater) error

	// VerifyVolumesAreAttachedPerNode verifies the given list of volumes to see whether they are still attached to the node.
	// If any volume is not attached right now, it will update the actual state of the world to reflect that.
	// Note that this operation could be operated concurrently with other attach/detach operations.
	// In theory (but very unlikely in practise), race condition among these operations might mark volume as detached
	// even if it is attached. But reconciler can correct this in a short period of time.
	VerifyVolumesAreAttachedPerNode(AttachedVolumes []AttachedVolume, nodeName types.NodeName, actualStateOfWorld ActualStateOfWorldAttacherUpdater) error

	// VerifyVolumesAreAttached verifies volumes being used in entire cluster and if they are still attached to the node
	// If any volume is not attached right now, it will update actual state of world to reflect that.
	VerifyVolumesAreAttached(volumesToVerify map[types.NodeName][]AttachedVolume, actualStateOfWorld ActualStateOfWorldAttacherUpdater)

	// DetachVolume detaches the volume from the node specified in
	// volumeToDetach, and updates the actual state of the world to reflect
	// that. If verifySafeToDetach is set, a call is made to the fetch the node
	// object and it is used to verify that the volume does not exist in Node's
	// Status.VolumesInUse list (operation fails with error if it is).
	DetachVolume(volumeToDetach AttachedVolume, verifySafeToDetach bool, actualStateOfWorld ActualStateOfWorldAttacherUpdater) error

	// If a volume has 'Filesystem' volumeMode, MountVolume mounts the
	// volume to the pod specified in volumeToMount.
	// Specifically it will:
	// * Wait for the device to finish attaching (for attachable volumes only).
	// * Mount device to global mount path (for attachable volumes only).
	// * Update actual state of world to reflect volume is globally mounted (for
	//   attachable volumes only).
	// * Mount the volume to the pod specific path.
	// * Update actual state of world to reflect volume is mounted to the pod
	//   path.
	// The parameter "isRemount" is informational and used to adjust logging
	// verbosity. An initial mount is more log-worthy than a remount, for
	// example.
	//
	// For 'Block' volumeMode, this method creates a symbolic link to
	// the volume from both the pod specified in volumeToMount and global map path.
	// Specifically it will:
	// * Wait for the device to finish attaching (for attachable volumes only).
	// * Update actual state of world to reflect volume is globally mounted/mapped.
	// * Map volume to global map path using symbolic link.
	// * Map the volume to the pod device map path using symbolic link.
	// * Update actual state of world to reflect volume is mounted/mapped to the pod path.
	MountVolume(waitForAttachTimeout time.Duration, volumeToMount VolumeToMount, actualStateOfWorld ActualStateOfWorldMounterUpdater, isRemount bool) error

	// If a volume has 'Filesystem' volumeMode, UnmountVolume unmounts the
	// volume from the pod specified in volumeToUnmount and updates the actual
	// state of the world to reflect that.
	//
	// For 'Block' volumeMode, this method unmaps symbolic link to the volume
	// from both the pod device map path in volumeToUnmount and global map path.
	// And then, updates the actual state of the world to reflect that.
	UnmountVolume(volumeToUnmount MountedVolume, actualStateOfWorld ActualStateOfWorldMounterUpdater, podsDir string) error

	// If a volume has 'Filesystem' volumeMode, UnmountDevice unmounts the
	// volumes global mount path from the device (for attachable volumes only,
	// freeing it for detach. It then updates the actual state of the world to
	// reflect that.
	//
	// For 'Block' volumeMode, this method checks number of symbolic links under
	// global map path. If number of reference is zero, remove global map path
	// directory and free a volume for detach.
	// It then updates the actual state of the world to reflect that.
	UnmountDevice(deviceToDetach AttachedVolume, actualStateOfWorld ActualStateOfWorldMounterUpdater, mounter mount.Interface) error

	// VerifyControllerAttachedVolume checks if the specified volume is present
	// in the specified nodes AttachedVolumes Status field. It uses kubeClient
	// to fetch the node object.
	// If the volume is found, the actual state of the world is updated to mark
	// the volume as attached.
	// If the volume does not implement the attacher interface, it is assumed to
	// be attached and the actual state of the world is updated accordingly.
	// If the volume is not found or there is an error (fetching the node
	// object, for example) then an error is returned which triggers exponential
	// back off on retries.
	VerifyControllerAttachedVolume(volumeToMount VolumeToMount, nodeName types.NodeName, actualStateOfWorld ActualStateOfWorldAttacherUpdater) error

	// IsOperationPending returns true if an operation for the given volumeName and podName is pending,
	// otherwise it returns false
	IsOperationPending(volumeName v1.UniqueVolumeName, podName volumetypes.UniquePodName) bool
	// Expand Volume will grow size available to PVC
	ExpandVolume(*expandcache.PVCWithResizeRequest, expandcache.VolumeResizeMap) error
	// ExpandVolumeFSWithoutUnmounting will resize volume's file system to expected size without unmounting the volume.
	ExpandVolumeFSWithoutUnmounting(volumeToMount VolumeToMount, actualStateOfWorld ActualStateOfWorldMounterUpdater) error
	// ReconstructVolumeOperation construct a new volumeSpec and returns it created by plugin
	ReconstructVolumeOperation(volumeMode v1.PersistentVolumeMode, plugin volume.VolumePlugin, mapperPlugin volume.BlockVolumePlugin, uid types.UID, podName volumetypes.UniquePodName, volumeSpecName string, mountPath string, pluginName string) (*volume.Spec, error)
	// CheckVolumeExistenceOperation checks volume existence
	CheckVolumeExistenceOperation(volumeSpec *volume.Spec, mountPath, volumeName string, mounter mount.Interface, uniqueVolumeName v1.UniqueVolumeName, podName volumetypes.UniquePodName, podUID types.UID, attachable volume.AttachableVolumePlugin) (bool, error)
}

// NewOperationExecutor returns a new instance of OperationExecutor.
func NewOperationExecutor(
	operationGenerator OperationGenerator) OperationExecutor {

	return &operationExecutor{
		pendingOperations: nestedpendingoperations.NewNestedPendingOperations(
			true /* exponentialBackOffOnError */),
		operationGenerator: operationGenerator,
	}
}

// ActualStateOfWorldMounterUpdater defines a set of operations updating the actual
// state of the world cache after successful mount/unmount.
type ActualStateOfWorldMounterUpdater interface {
	// Marks the specified volume as mounted to the specified pod
	MarkVolumeAsMounted(podName volumetypes.UniquePodName, podUID types.UID, volumeName v1.UniqueVolumeName, mounter volume.Mounter, blockVolumeMapper volume.BlockVolumeMapper, outerVolumeSpecName string, volumeGidValue string, volumeSpec *volume.Spec) error

	// Marks the specified volume as unmounted from the specified pod
	MarkVolumeAsUnmounted(podName volumetypes.UniquePodName, volumeName v1.UniqueVolumeName) error

	// Marks the specified volume as having been globally mounted.
	MarkDeviceAsMounted(volumeName v1.UniqueVolumeName, devicePath, deviceMountPath string) error

	// Marks the specified volume as having its global mount unmounted.
	MarkDeviceAsUnmounted(volumeName v1.UniqueVolumeName) error

	// Marks the specified volume's file system resize request is finished.
	MarkVolumeAsResized(podName volumetypes.UniquePodName, volumeName v1.UniqueVolumeName) error
}

// ActualStateOfWorldAttacherUpdater defines a set of operations updating the
// actual state of the world cache after successful attach/detach/mount/unmount.
type ActualStateOfWorldAttacherUpdater interface {
	// Marks the specified volume as attached to the specified node.  If the
	// volume name is supplied, that volume name will be used.  If not, the
	// volume name is computed using the result from querying the plugin.
	//
	// TODO: in the future, we should be able to remove the volumeName
	// argument to this method -- since it is used only for attachable
	// volumes.  See issue 29695.
	MarkVolumeAsAttached(volumeName v1.UniqueVolumeName, volumeSpec *volume.Spec, nodeName types.NodeName, devicePath string) error

	// Marks the specified volume as detached from the specified node
	MarkVolumeAsDetached(volumeName v1.UniqueVolumeName, nodeName types.NodeName)

	// Marks desire to detach the specified volume (remove the volume from the node's
	// volumesToReportAsAttached list)
	RemoveVolumeFromReportAsAttached(volumeName v1.UniqueVolumeName, nodeName types.NodeName) error

	// Unmarks the desire to detach for the specified volume (add the volume back to
	// the node's volumesToReportAsAttached list)
	AddVolumeToReportAsAttached(volumeName v1.UniqueVolumeName, nodeName types.NodeName)
}

// VolumeLogger defines a set of operations for generating volume-related logging and error msgs
type VolumeLogger interface {
	// Creates a detailed msg that can be used in logs
	// The msg format follows the pattern "<prefixMsg> <volume details> <suffixMsg>",
	// where each implementation provides the volume details
	GenerateMsgDetailed(prefixMsg, suffixMsg string) (detailedMsg string)

	// Creates a detailed error that can be used in logs.
	// The msg format follows the pattern "<prefixMsg> <volume details>: <err> ",
	GenerateErrorDetailed(prefixMsg string, err error) (detailedErr error)

	// Creates a simple msg that is user friendly and a detailed msg that can be used in logs
	// The msg format follows the pattern "<prefixMsg> <volume details> <suffixMsg>",
	// where each implementation provides the volume details
	GenerateMsg(prefixMsg, suffixMsg string) (simpleMsg, detailedMsg string)

	// Creates a simple error that is user friendly and a detailed error that can be used in logs.
	// The msg format follows the pattern "<prefixMsg> <volume details>: <err> ",
	GenerateError(prefixMsg string, err error) (simpleErr, detailedErr error)
}

// Generates an error string with the format ": <err>" if err exists
func errSuffix(err error) string {
	errStr := ""
	if err != nil {
		errStr = fmt.Sprintf(": %v", err)
	}
	return errStr
}

// Generate a detailed error msg for logs
func generateVolumeMsgDetailed(prefixMsg, suffixMsg, volumeName, details string) (detailedMsg string) {
	return fmt.Sprintf("%v for volume %q %v %v", prefixMsg, volumeName, details, suffixMsg)
}

// Generate a simplified error msg for events and a detailed error msg for logs
func generateVolumeMsg(prefixMsg, suffixMsg, volumeName, details string) (simpleMsg, detailedMsg string) {
	simpleMsg = fmt.Sprintf("%v for volume %q %v", prefixMsg, volumeName, suffixMsg)
	return simpleMsg, generateVolumeMsgDetailed(prefixMsg, suffixMsg, volumeName, details)
}

// VolumeToAttach represents a volume that should be attached to a node.
type VolumeToAttach struct {
	// MultiAttachErrorReported indicates whether the multi-attach error has been reported for the given volume.
	// It is used to to prevent reporting the error from being reported more than once for a given volume.
	MultiAttachErrorReported bool

	// VolumeName is the unique identifier for the volume that should be
	// attached.
	VolumeName v1.UniqueVolumeName

	// VolumeSpec is a volume spec containing the specification for the volume
	// that should be attached.
	VolumeSpec *volume.Spec

	// NodeName is the identifier for the node that the volume should be
	// attached to.
	NodeName types.NodeName

	// scheduledPods is a map containing the set of pods that reference this
	// volume and are scheduled to the underlying node. The key in the map is
	// the name of the pod and the value is a pod object containing more
	// information about the pod.
	ScheduledPods []*v1.Pod
}

// GenerateMsgDetailed returns detailed msgs for volumes to attach
func (volume *VolumeToAttach) GenerateMsgDetailed(prefixMsg, suffixMsg string) (detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) from node %q", volume.VolumeName, volume.NodeName)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsgDetailed(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateMsg returns simple and detailed msgs for volumes to attach
func (volume *VolumeToAttach) GenerateMsg(prefixMsg, suffixMsg string) (simpleMsg, detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) from node %q", volume.VolumeName, volume.NodeName)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsg(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateErrorDetailed returns detailed errors for volumes to attach
func (volume *VolumeToAttach) GenerateErrorDetailed(prefixMsg string, err error) (detailedErr error) {
	return fmt.Errorf(volume.GenerateMsgDetailed(prefixMsg, errSuffix(err)))
}

// GenerateError returns simple and detailed errors for volumes to attach
func (volume *VolumeToAttach) GenerateError(prefixMsg string, err error) (simpleErr, detailedErr error) {
	simpleMsg, detailedMsg := volume.GenerateMsg(prefixMsg, errSuffix(err))
	return fmt.Errorf(simpleMsg), fmt.Errorf(detailedMsg)
}

// VolumeToMount represents a volume that should be attached to this node and
// mounted to the PodName.
type VolumeToMount struct {
	// VolumeName is the unique identifier for the volume that should be
	// mounted.
	VolumeName v1.UniqueVolumeName

	// PodName is the unique identifier for the pod that the volume should be
	// mounted to after it is attached.
	PodName volumetypes.UniquePodName

	// VolumeSpec is a volume spec containing the specification for the volume
	// that should be mounted. Used to create NewMounter. Used to generate
	// InnerVolumeSpecName.
	VolumeSpec *volume.Spec

	// outerVolumeSpecName is the podSpec.Volume[x].Name of the volume. If the
	// volume was referenced through a persistent volume claim, this contains
	// the podSpec.Volume[x].Name of the persistent volume claim.
	OuterVolumeSpecName string

	// Pod to mount the volume to. Used to create NewMounter.
	Pod *v1.Pod

	// PluginIsAttachable indicates that the plugin for this volume implements
	// the volume.Attacher interface
	PluginIsAttachable bool

	// VolumeGidValue contains the value of the GID annotation, if present.
	VolumeGidValue string

	// DevicePath contains the path on the node where the volume is attached.
	// For non-attachable volumes this is empty.
	DevicePath string

	// ReportedInUse indicates that the volume was successfully added to the
	// VolumesInUse field in the node's status.
	ReportedInUse bool
}

// GenerateMsgDetailed returns detailed msgs for volumes to mount
func (volume *VolumeToMount) GenerateMsgDetailed(prefixMsg, suffixMsg string) (detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) pod %q (UID: %q)", volume.VolumeName, volume.Pod.Name, volume.Pod.UID)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsgDetailed(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateMsg returns simple and detailed msgs for volumes to mount
func (volume *VolumeToMount) GenerateMsg(prefixMsg, suffixMsg string) (simpleMsg, detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) pod %q (UID: %q)", volume.VolumeName, volume.Pod.Name, volume.Pod.UID)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsg(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateErrorDetailed returns detailed errors for volumes to mount
func (volume *VolumeToMount) GenerateErrorDetailed(prefixMsg string, err error) (detailedErr error) {
	return fmt.Errorf(volume.GenerateMsgDetailed(prefixMsg, errSuffix(err)))
}

// GenerateError returns simple and detailed errors for volumes to mount
func (volume *VolumeToMount) GenerateError(prefixMsg string, err error) (simpleErr, detailedErr error) {
	simpleMsg, detailedMsg := volume.GenerateMsg(prefixMsg, errSuffix(err))
	return fmt.Errorf(simpleMsg), fmt.Errorf(detailedMsg)
}

// AttachedVolume represents a volume that is attached to a node.
type AttachedVolume struct {
	// VolumeName is the unique identifier for the volume that is attached.
	VolumeName v1.UniqueVolumeName

	// VolumeSpec is the volume spec containing the specification for the
	// volume that is attached.
	VolumeSpec *volume.Spec

	// NodeName is the identifier for the node that the volume is attached to.
	NodeName types.NodeName

	// PluginIsAttachable indicates that the plugin for this volume implements
	// the volume.Attacher interface
	PluginIsAttachable bool

	// DevicePath contains the path on the node where the volume is attached.
	// For non-attachable volumes this is empty.
	DevicePath string

	// DeviceMountPath contains the path on the node where the device should
	// be mounted after it is attached.
	DeviceMountPath string

	// PluginName is the Unescaped Qualified name of the volume plugin used to
	// attach and mount this volume.
	PluginName string
}

// GenerateMsgDetailed returns detailed msgs for attached volumes
func (volume *AttachedVolume) GenerateMsgDetailed(prefixMsg, suffixMsg string) (detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) on node %q", volume.VolumeName, volume.NodeName)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsgDetailed(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateMsg returns simple and detailed msgs for attached volumes
func (volume *AttachedVolume) GenerateMsg(prefixMsg, suffixMsg string) (simpleMsg, detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) on node %q", volume.VolumeName, volume.NodeName)
	volumeSpecName := "nil"
	if volume.VolumeSpec != nil {
		volumeSpecName = volume.VolumeSpec.Name()
	}
	return generateVolumeMsg(prefixMsg, suffixMsg, volumeSpecName, detailedStr)
}

// GenerateErrorDetailed returns detailed errors for attached volumes
func (volume *AttachedVolume) GenerateErrorDetailed(prefixMsg string, err error) (detailedErr error) {
	return fmt.Errorf(volume.GenerateMsgDetailed(prefixMsg, errSuffix(err)))
}

// GenerateError returns simple and detailed errors for attached volumes
func (volume *AttachedVolume) GenerateError(prefixMsg string, err error) (simpleErr, detailedErr error) {
	simpleMsg, detailedMsg := volume.GenerateMsg(prefixMsg, errSuffix(err))
	return fmt.Errorf(simpleMsg), fmt.Errorf(detailedMsg)
}

// MountedVolume represents a volume that has successfully been mounted to a pod.
type MountedVolume struct {
	// PodName is the unique identifier of the pod mounted to.
	PodName volumetypes.UniquePodName

	// VolumeName is the unique identifier of the volume mounted to the pod.
	VolumeName v1.UniqueVolumeName

	// InnerVolumeSpecName is the volume.Spec.Name() of the volume. If the
	// volume was referenced through a persistent volume claims, this contains
	// the name of the bound persistent volume object.
	// It is the name that plugins use in their pod mount path, i.e.
	// /var/lib/kubelet/pods/{podUID}/volumes/{escapeQualifiedPluginName}/{innerVolumeSpecName}/
	// PVC example,
	//   apiVersion: v1
	//   kind: PersistentVolume
	//   metadata:
	//     name: pv0003				<- InnerVolumeSpecName
	//   spec:
	//     capacity:
	//       storage: 5Gi
	//     accessModes:
	//       - ReadWriteOnce
	//     persistentVolumeReclaimPolicy: Recycle
	//     nfs:
	//       path: /tmp
	//       server: 172.17.0.2
	// Non-PVC example:
	//   apiVersion: v1
	//   kind: Pod
	//   metadata:
	//     name: test-pd
	//   spec:
	//     containers:
	//     - image: k8s.gcr.io/test-webserver
	//     	 name: test-container
	//     	 volumeMounts:
	//     	 - mountPath: /test-pd
	//     	   name: test-volume
	//     volumes:
	//     - name: test-volume			<- InnerVolumeSpecName
	//     	 gcePersistentDisk:
	//     	   pdName: my-data-disk
	//     	   fsType: ext4
	InnerVolumeSpecName string

	// outerVolumeSpecName is the podSpec.Volume[x].Name of the volume. If the
	// volume was referenced through a persistent volume claim, this contains
	// the podSpec.Volume[x].Name of the persistent volume claim.
	// PVC example:
	//   kind: Pod
	//   apiVersion: v1
	//   metadata:
	//     name: mypod
	//   spec:
	//     containers:
	//       - name: myfrontend
	//         image: dockerfile/nginx
	//         volumeMounts:
	//         - mountPath: "/var/www/html"
	//           name: mypd
	//     volumes:
	//       - name: mypd				<- OuterVolumeSpecName
	//         persistentVolumeClaim:
	//           claimName: myclaim
	// Non-PVC example:
	//   apiVersion: v1
	//   kind: Pod
	//   metadata:
	//     name: test-pd
	//   spec:
	//     containers:
	//     - image: k8s.gcr.io/test-webserver
	//     	 name: test-container
	//     	 volumeMounts:
	//     	 - mountPath: /test-pd
	//     	   name: test-volume
	//     volumes:
	//     - name: test-volume			<- OuterVolumeSpecName
	//     	 gcePersistentDisk:
	//     	   pdName: my-data-disk
	//     	   fsType: ext4
	OuterVolumeSpecName string

	// PluginName is the "Unescaped Qualified" name of the volume plugin used to
	// mount and unmount this volume. It can be used to fetch the volume plugin
	// to unmount with, on demand. It is also the name that plugins use, though
	// escaped, in their pod mount path, i.e.
	// /var/lib/kubelet/pods/{podUID}/volumes/{escapeQualifiedPluginName}/{outerVolumeSpecName}/
	PluginName string

	// PodUID is the UID of the pod mounted to. It is also the string used by
	// plugins in their pod mount path, i.e.
	// /var/lib/kubelet/pods/{podUID}/volumes/{escapeQualifiedPluginName}/{outerVolumeSpecName}/
	PodUID types.UID

	// Mounter is the volume mounter used to mount this volume. It is required
	// by kubelet to create container.VolumeMap.
	Mounter volume.Mounter

	// BlockVolumeMapper is the volume mapper used to map this volume. It is required
	// by kubelet to create container.VolumeMap.
	BlockVolumeMapper volume.BlockVolumeMapper

	// VolumeGidValue contains the value of the GID annotation, if present.
	VolumeGidValue string

	// VolumeSpec is a volume spec containing the specification for the volume
	// that should be mounted.
	VolumeSpec *volume.Spec

	// DeviceMountPath contains the path on the node where the device should
	// be mounted after it is attached.
	DeviceMountPath string
}

// GenerateMsgDetailed returns detailed msgs for mounted volumes
func (volume *MountedVolume) GenerateMsgDetailed(prefixMsg, suffixMsg string) (detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) pod %q (UID: %q)", volume.VolumeName, volume.PodName, volume.PodUID)
	return generateVolumeMsgDetailed(prefixMsg, suffixMsg, volume.OuterVolumeSpecName, detailedStr)
}

// GenerateMsg returns simple and detailed msgs for mounted volumes
func (volume *MountedVolume) GenerateMsg(prefixMsg, suffixMsg string) (simpleMsg, detailedMsg string) {
	detailedStr := fmt.Sprintf("(UniqueName: %q) pod %q (UID: %q)", volume.VolumeName, volume.PodName, volume.PodUID)
	return generateVolumeMsg(prefixMsg, suffixMsg, volume.OuterVolumeSpecName, detailedStr)
}

// GenerateErrorDetailed returns simple and detailed errors for mounted volumes
func (volume *MountedVolume) GenerateErrorDetailed(prefixMsg string, err error) (detailedErr error) {
	return fmt.Errorf(volume.GenerateMsgDetailed(prefixMsg, errSuffix(err)))
}

// GenerateError returns simple and detailed errors for mounted volumes
func (volume *MountedVolume) GenerateError(prefixMsg string, err error) (simpleErr, detailedErr error) {
	simpleMsg, detailedMsg := volume.GenerateMsg(prefixMsg, errSuffix(err))
	return fmt.Errorf(simpleMsg), fmt.Errorf(detailedMsg)
}

type operationExecutor struct {
	// pendingOperations keeps track of pending attach and detach operations so
	// multiple operations are not started on the same volume
	pendingOperations nestedpendingoperations.NestedPendingOperations

	// operationGenerator is an interface that provides implementations for
	// generating volume function
	operationGenerator OperationGenerator
}

func (oe *operationExecutor) IsOperationPending(volumeName v1.UniqueVolumeName, podName volumetypes.UniquePodName) bool {
	return oe.pendingOperations.IsOperationPending(volumeName, podName)
}

func (oe *operationExecutor) AttachVolume(
	volumeToAttach VolumeToAttach,
	actualStateOfWorld ActualStateOfWorldAttacherUpdater) error {
	generatedOperations, err :=
		oe.operationGenerator.GenerateAttachVolumeFunc(volumeToAttach, actualStateOfWorld)
	if err != nil {
		return err
	}

	return oe.pendingOperations.Run(
		volumeToAttach.VolumeName, "" /* podName */, generatedOperations)
}

func (oe *operationExecutor) DetachVolume(
	volumeToDetach AttachedVolume,
	verifySafeToDetach bool,
	actualStateOfWorld ActualStateOfWorldAttacherUpdater) error {
	generatedOperations, err :=
		oe.operationGenerator.GenerateDetachVolumeFunc(volumeToDetach, verifySafeToDetach, actualStateOfWorld)
	if err != nil {
		return err
	}

	return oe.pendingOperations.Run(
		volumeToDetach.VolumeName, "" /* podName */, generatedOperations)
}

func (oe *operationExecutor) VerifyVolumesAreAttached(
	attachedVolumes map[types.NodeName][]AttachedVolume,
	actualStateOfWorld ActualStateOfWorldAttacherUpdater) {

	// A map of plugin names and nodes on which they exist with volumes they manage
	bulkVerifyPluginsByNode := make(map[string]map[types.NodeName][]*volume.Spec)
	volumeSpecMapByPlugin := make(map[string]map[*volume.Spec]v1.UniqueVolumeName)

	for node, nodeAttachedVolumes := range attachedVolumes {
		for _, volumeAttached := range nodeAttachedVolumes {
			if volumeAttached.VolumeSpec == nil {
				glog.Errorf("VerifyVolumesAreAttached: nil spec for volume %s", volumeAttached.VolumeName)
				continue
			}
			volumePlugin, err :=
				oe.operationGenerator.GetVolumePluginMgr().FindPluginBySpec(volumeAttached.VolumeSpec)

			if err != nil || volumePlugin == nil {
				glog.Errorf(
					"VolumesAreAttached.FindPluginBySpec failed for volume %q (spec.Name: %q) on node %q with error: %v",
					volumeAttached.VolumeName,
					volumeAttached.VolumeSpec.Name(),
					volumeAttached.NodeName,
					err)
				continue
			}

			pluginName := volumePlugin.GetPluginName()

			if volumePlugin.SupportsBulkVolumeVerification() {
				pluginNodes, pluginNodesExist := bulkVerifyPluginsByNode[pluginName]

				if !pluginNodesExist {
					pluginNodes = make(map[types.NodeName][]*volume.Spec)
				}

				volumeSpecList, nodeExists := pluginNodes[node]
				if !nodeExists {
					volumeSpecList = []*volume.Spec{}
				}
				volumeSpecList = append(volumeSpecList, volumeAttached.VolumeSpec)
				pluginNodes[node] = volumeSpecList

				bulkVerifyPluginsByNode[pluginName] = pluginNodes
				volumeSpecMap, mapExists := volumeSpecMapByPlugin[pluginName]

				if !mapExists {
					volumeSpecMap = make(map[*volume.Spec]v1.UniqueVolumeName)
				}
				volumeSpecMap[volumeAttached.VolumeSpec] = volumeAttached.VolumeName
				volumeSpecMapByPlugin[pluginName] = volumeSpecMap
				continue
			}

			// If node doesn't support Bulk volume polling it is best to poll individually
			nodeError := oe.VerifyVolumesAreAttachedPerNode(nodeAttachedVolumes, node, actualStateOfWorld)
			if nodeError != nil {
				glog.Errorf("BulkVerifyVolumes.VerifyVolumesAreAttached verifying volumes on node %q with %v", node, nodeError)
			}
			break
		}
	}

	for pluginName, pluginNodeVolumes := range bulkVerifyPluginsByNode {
		generatedOperations, err := oe.operationGenerator.GenerateBulkVolumeVerifyFunc(
			pluginNodeVolumes,
			pluginName,
			volumeSpecMapByPlugin[pluginName],
			actualStateOfWorld)
		if err != nil {
			glog.Errorf("BulkVerifyVolumes.GenerateBulkVolumeVerifyFunc error bulk verifying volumes for plugin %q with  %v", pluginName, err)
		}

		// Ugly hack to ensure - we don't do parallel bulk polling of same volume plugin
		uniquePluginName := v1.UniqueVolumeName(pluginName)
		err = oe.pendingOperations.Run(uniquePluginName, "" /* Pod Name */, generatedOperations)
		if err != nil {
			glog.Errorf("BulkVerifyVolumes.Run Error bulk volume verification for plugin %q  with %v", pluginName, err)
		}
	}
}

func (oe *operationExecutor) VerifyVolumesAreAttachedPerNode(
	attachedVolumes []AttachedVolume,
	nodeName types.NodeName,
	actualStateOfWorld ActualStateOfWorldAttacherUpdater) error {
	generatedOperations, err :=
		oe.operationGenerator.GenerateVolumesAreAttachedFunc(attachedVolumes, nodeName, actualStateOfWorld)
	if err != nil {
		return err
	}

	// Give an empty UniqueVolumeName so that this operation could be executed concurrently.
	return oe.pendingOperations.Run("" /* volumeName */, "" /* podName */, generatedOperations)
}

func (oe *operationExecutor) MountVolume(
	waitForAttachTimeout time.Duration,
	volumeToMount VolumeToMount,
	actualStateOfWorld ActualStateOfWorldMounterUpdater,
	isRemount bool) error {
	fsVolume, err := util.CheckVolumeModeFilesystem(volumeToMount.VolumeSpec)
	if err != nil {
		return err
	}
	var generatedOperations volumetypes.GeneratedOperations
	if fsVolume {
		// Filesystem volume case
		// Mount/remount a volume when a volume is attached
		generatedOperations, err = oe.operationGenerator.GenerateMountVolumeFunc(
			waitForAttachTimeout, volumeToMount, actualStateOfWorld, isRemount)

	} else {
		// Block volume case
		// Creates a map to device if a volume is attached
		generatedOperations, err = oe.operationGenerator.GenerateMapVolumeFunc(
			waitForAttachTimeout, volumeToMount, actualStateOfWorld)
	}
	if err != nil {
		return err
	}
	// Avoid executing mount/map from multiple pods referencing the
	// same volume in parallel
	podName := nestedpendingoperations.EmptyUniquePodName

	// TODO: remove this -- not necessary
	if !volumeToMount.PluginIsAttachable {
		// Non-attachable volume plugins can execute mount for multiple pods
		// referencing the same volume in parallel
		podName = util.GetUniquePodName(volumeToMount.Pod)
	}

	// TODO mount_device
	return oe.pendingOperations.Run(
		volumeToMount.VolumeName, podName, generatedOperations)
}

func (oe *operationExecutor) UnmountVolume(
	volumeToUnmount MountedVolume,
	actualStateOfWorld ActualStateOfWorldMounterUpdater,
	podsDir string) error {
	fsVolume, err := util.CheckVolumeModeFilesystem(volumeToUnmount.VolumeSpec)
	if err != nil {
		return err
	}
	var generatedOperations volumetypes.GeneratedOperations
	if fsVolume {
		// Filesystem volume case
		// Unmount a volume if a volume is mounted
		generatedOperations, err = oe.operationGenerator.GenerateUnmountVolumeFunc(
			volumeToUnmount, actualStateOfWorld, podsDir)
	} else {
		// Block volume case
		// Unmap a volume if a volume is mapped
		generatedOperations, err = oe.operationGenerator.GenerateUnmapVolumeFunc(
			volumeToUnmount, actualStateOfWorld)
	}
	if err != nil {
		return err
	}
	// All volume plugins can execute unmount/unmap for multiple pods referencing the
	// same volume in parallel
	podName := volumetypes.UniquePodName(volumeToUnmount.PodUID)

	return oe.pendingOperations.Run(
		volumeToUnmount.VolumeName, podName, generatedOperations)
}

func (oe *operationExecutor) UnmountDevice(
	deviceToDetach AttachedVolume,
	actualStateOfWorld ActualStateOfWorldMounterUpdater,
	mounter mount.Interface) error {
	fsVolume, err := util.CheckVolumeModeFilesystem(deviceToDetach.VolumeSpec)
	if err != nil {
		return err
	}
	var generatedOperations volumetypes.GeneratedOperations
	if fsVolume {
		// Filesystem volume case
		// Unmount and detach a device if a volume isn't referenced
		generatedOperations, err = oe.operationGenerator.GenerateUnmountDeviceFunc(
			deviceToDetach, actualStateOfWorld, mounter)
	} else {
		// Block volume case
		// Detach a device and remove loopback if a volume isn't referenced
		generatedOperations, err = oe.operationGenerator.GenerateUnmapDeviceFunc(
			deviceToDetach, actualStateOfWorld, mounter)
	}
	if err != nil {
		return err
	}
	// Avoid executing unmount/unmap device from multiple pods referencing
	// the same volume in parallel
	podName := nestedpendingoperations.EmptyUniquePodName

	return oe.pendingOperations.Run(
		deviceToDetach.VolumeName, podName, generatedOperations)
}

func (oe *operationExecutor) ExpandVolume(pvcWithResizeRequest *expandcache.PVCWithResizeRequest, resizeMap expandcache.VolumeResizeMap) error {
	generatedOperations, err := oe.operationGenerator.GenerateExpandVolumeFunc(pvcWithResizeRequest, resizeMap)

	if err != nil {
		return err
	}
	uniqueVolumeKey := v1.UniqueVolumeName(pvcWithResizeRequest.UniquePVCKey())

	return oe.pendingOperations.Run(uniqueVolumeKey, "", generatedOperations)
}

func (oe *operationExecutor) ExpandVolumeFSWithoutUnmounting(volumeToMount VolumeToMount, actualStateOfWorld ActualStateOfWorldMounterUpdater) error {
	generatedOperations, err := oe.operationGenerator.GenerateExpandVolumeFSWithoutUnmountingFunc(volumeToMount, actualStateOfWorld)
	if err != nil {
		return err
	}
	return oe.pendingOperations.Run(volumeToMount.VolumeName, "", generatedOperations)
}

func (oe *operationExecutor) VerifyControllerAttachedVolume(
	volumeToMount VolumeToMount,
	nodeName types.NodeName,
	actualStateOfWorld ActualStateOfWorldAttacherUpdater) error {
	generatedOperations, err :=
		oe.operationGenerator.GenerateVerifyControllerAttachedVolumeFunc(volumeToMount, nodeName, actualStateOfWorld)
	if err != nil {
		return err
	}

	return oe.pendingOperations.Run(
		volumeToMount.VolumeName, "" /* podName */, generatedOperations)
}

// ReconstructVolumeOperation return a func to create volumeSpec from mount path
func (oe *operationExecutor) ReconstructVolumeOperation(
	volumeMode v1.PersistentVolumeMode,
	plugin volume.VolumePlugin,
	mapperPlugin volume.BlockVolumePlugin,
	uid types.UID,
	podName volumetypes.UniquePodName,
	volumeSpecName string,
	mountPath string,
	pluginName string) (*volume.Spec, error) {

	// Filesystem Volume case
	if volumeMode == v1.PersistentVolumeFilesystem {
		// Create volumeSpec from mount path
		glog.V(5).Infof("Starting operationExecutor.ReconstructVolumepodName")
		volumeSpec, err := plugin.ConstructVolumeSpec(volumeSpecName, mountPath)
		if err != nil {
			return nil, err
		}
		return volumeSpec, nil
	}

	// Block Volume case
	// Create volumeSpec from mount path
	glog.V(5).Infof("Starting operationExecutor.ReconstructVolume")
	if mapperPlugin == nil {
		return nil, fmt.Errorf("Could not find block volume plugin %q (spec.Name: %q) pod %q (UID: %q)",
			pluginName,
			volumeSpecName,
			podName,
			uid)
	}
	// mountPath contains volumeName on the path. In the case of block volume, {volumeName} is symbolic link
	// corresponding to raw block device.
	// ex. mountPath: pods/{podUid}}/{DefaultKubeletVolumeDevicesDirName}/{escapeQualifiedPluginName}/{volumeName}
	volumeSpec, err := mapperPlugin.ConstructBlockVolumeSpec(uid, volumeSpecName, mountPath)
	if err != nil {
		return nil, err
	}
	return volumeSpec, nil
}

// CheckVolumeExistenceOperation return a func() to check mount path directory if volume still exists
func (oe *operationExecutor) CheckVolumeExistenceOperation(
	volumeSpec *volume.Spec,
	mountPath, volumeName string,
	mounter mount.Interface,
	uniqueVolumeName v1.UniqueVolumeName,
	podName volumetypes.UniquePodName,
	podUID types.UID,
	attachable volume.AttachableVolumePlugin) (bool, error) {
	fsVolume, err := util.CheckVolumeModeFilesystem(volumeSpec)
	if err != nil {
		return false, err
	}

	// Filesystem Volume case
	// For attachable volume case, check mount path directory if volume is still existing and mounted.
	// Return true if volume is mounted.
	if fsVolume {
		if attachable != nil {
			var isNotMount bool
			var mountCheckErr error
			if isNotMount, mountCheckErr = mounter.IsLikelyNotMountPoint(mountPath); mountCheckErr != nil {
				return false, fmt.Errorf("Could not check whether the volume %q (spec.Name: %q) pod %q (UID: %q) is mounted with: %v",
					uniqueVolumeName,
					volumeName,
					podName,
					podUID,
					mountCheckErr)
			}
			return !isNotMount, nil
		}
		// For non-attachable volume case, skip check and return true without mount point check
		// since plugins may not have volume mount point.
		return true, nil
	}

	// Block Volume case
	// Check mount path directory if volume still exists, then return true if volume
	// is there. Either plugin is attachable or non-attachable, the plugin should
	// have symbolic link associated to raw block device under pod device map
	// if volume exists.
	blkutil := volumepathhandler.NewBlockVolumePathHandler()
	var islinkExist bool
	var checkErr error
	if islinkExist, checkErr = blkutil.IsSymlinkExist(mountPath); checkErr != nil {
		return false, fmt.Errorf("Could not check whether the block volume %q (spec.Name: %q) pod %q (UID: %q) is mapped to: %v",
			uniqueVolumeName,
			volumeName,
			podName,
			podUID,
			checkErr)
	}
	return islinkExist, nil
}