manager.go

/*
Copyright 2017 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 devicemanager

import (
	"context"
	"fmt"
	"net"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/golang/glog"
	"google.golang.org/grpc"

	"k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/resource"
	"k8s.io/apimachinery/pkg/util/sets"
	v1helper "k8s.io/kubernetes/pkg/apis/core/v1/helper"
	pluginapi "k8s.io/kubernetes/pkg/kubelet/apis/deviceplugin/v1beta1"
	"k8s.io/kubernetes/pkg/kubelet/checkpointmanager"
	"k8s.io/kubernetes/pkg/kubelet/checkpointmanager/errors"
	"k8s.io/kubernetes/pkg/kubelet/cm/devicemanager/checkpoint"
	"k8s.io/kubernetes/pkg/kubelet/config"
	"k8s.io/kubernetes/pkg/kubelet/lifecycle"
	"k8s.io/kubernetes/pkg/kubelet/metrics"
	watcher "k8s.io/kubernetes/pkg/kubelet/util/pluginwatcher"
	schedulercache "k8s.io/kubernetes/pkg/scheduler/cache"
)

// ActivePodsFunc is a function that returns a list of pods to reconcile.
type ActivePodsFunc func() []*v1.Pod

// monitorCallback is the function called when a device's health state changes,
// or new devices are reported, or old devices are deleted.
// Updated contains the most recent state of the Device.
type monitorCallback func(resourceName string, devices []pluginapi.Device)

// ManagerImpl is the structure in charge of managing Device Plugins.
type ManagerImpl struct {
	socketname string
	socketdir  string

	endpoints map[string]endpointInfo // Key is ResourceName
	mutex     sync.Mutex

	server *grpc.Server
	wg     sync.WaitGroup

	// activePods is a method for listing active pods on the node
	// so the amount of pluginResources requested by existing pods
	// could be counted when updating allocated devices
	activePods ActivePodsFunc

	// sourcesReady provides the readiness of kubelet configuration sources such as apiserver update readiness.
	// We use it to determine when we can purge inactive pods from checkpointed state.
	sourcesReady config.SourcesReady

	// callback is used for updating devices' states in one time call.
	// e.g. a new device is advertised, two old devices are deleted and a running device fails.
	callback monitorCallback

	// healthyDevices contains all of the registered healthy resourceNames and their exported device IDs.
	healthyDevices map[string]sets.String

	// unhealthyDevices contains all of the unhealthy devices and their exported device IDs.
	unhealthyDevices map[string]sets.String

	// allocatedDevices contains allocated deviceIds, keyed by resourceName.
	allocatedDevices map[string]sets.String

	// podDevices contains pod to allocated device mapping.
	podDevices        podDevices
	checkpointManager checkpointmanager.CheckpointManager
}

type endpointInfo struct {
	e    endpoint
	opts *pluginapi.DevicePluginOptions
}

type sourcesReadyStub struct{}

func (s *sourcesReadyStub) AddSource(source string) {}
func (s *sourcesReadyStub) AllReady() bool          { return true }

// NewManagerImpl creates a new manager.
func NewManagerImpl() (*ManagerImpl, error) {
	return newManagerImpl(pluginapi.KubeletSocket)
}

func newManagerImpl(socketPath string) (*ManagerImpl, error) {
	glog.V(2).Infof("Creating Device Plugin manager at %s", socketPath)

	if socketPath == "" || !filepath.IsAbs(socketPath) {
		return nil, fmt.Errorf(errBadSocket+" %s", socketPath)
	}

	dir, file := filepath.Split(socketPath)
	manager := &ManagerImpl{
		endpoints: make(map[string]endpointInfo),

		socketname:       file,
		socketdir:        dir,
		healthyDevices:   make(map[string]sets.String),
		unhealthyDevices: make(map[string]sets.String),
		allocatedDevices: make(map[string]sets.String),
		podDevices:       make(podDevices),
	}
	manager.callback = manager.genericDeviceUpdateCallback

	// The following structs are populated with real implementations in manager.Start()
	// Before that, initializes them to perform no-op operations.
	manager.activePods = func() []*v1.Pod { return []*v1.Pod{} }
	manager.sourcesReady = &sourcesReadyStub{}
	checkpointManager, err := checkpointmanager.NewCheckpointManager(dir)
	if err != nil {
		return nil, fmt.Errorf("failed to initialize checkpoint manager: %v", err)
	}
	manager.checkpointManager = checkpointManager

	return manager, nil
}

func (m *ManagerImpl) genericDeviceUpdateCallback(resourceName string, devices []pluginapi.Device) {
	m.mutex.Lock()
	m.healthyDevices[resourceName] = sets.NewString()
	m.unhealthyDevices[resourceName] = sets.NewString()
	for _, dev := range devices {
		if dev.Health == pluginapi.Healthy {
			m.healthyDevices[resourceName].Insert(dev.ID)
		} else {
			m.unhealthyDevices[resourceName].Insert(dev.ID)
		}
	}
	m.mutex.Unlock()
	m.writeCheckpoint()
}

func (m *ManagerImpl) removeContents(dir string) error {
	d, err := os.Open(dir)
	if err != nil {
		return err
	}
	defer d.Close()
	names, err := d.Readdirnames(-1)
	if err != nil {
		return err
	}
	for _, name := range names {
		filePath := filepath.Join(dir, name)
		if filePath == m.checkpointFile() {
			continue
		}
		stat, err := os.Stat(filePath)
		if err != nil {
			glog.Errorf("Failed to stat file %s: %v", filePath, err)
			continue
		}
		if stat.IsDir() {
			continue
		}
		err = os.RemoveAll(filePath)
		if err != nil {
			return err
		}
	}
	return nil
}

// checkpointFile returns device plugin checkpoint file path.
func (m *ManagerImpl) checkpointFile() string {
	return filepath.Join(m.socketdir, kubeletDeviceManagerCheckpoint)
}

// Start starts the Device Plugin Manager amd start initialization of
// podDevices and allocatedDevices information from checkpoint-ed state and
// starts device plugin registration service.
func (m *ManagerImpl) Start(activePods ActivePodsFunc, sourcesReady config.SourcesReady) error {
	glog.V(2).Infof("Starting Device Plugin manager")

	m.activePods = activePods
	m.sourcesReady = sourcesReady

	// Loads in allocatedDevices information from disk.
	err := m.readCheckpoint()
	if err != nil {
		glog.Warningf("Continue after failing to read checkpoint file. Device allocation info may NOT be up-to-date. Err: %v", err)
	}

	socketPath := filepath.Join(m.socketdir, m.socketname)
	os.MkdirAll(m.socketdir, 0755)

	// Removes all stale sockets in m.socketdir. Device plugins can monitor
	// this and use it as a signal to re-register with the new Kubelet.
	if err := m.removeContents(m.socketdir); err != nil {
		glog.Errorf("Fail to clean up stale contents under %s: %v", m.socketdir, err)
	}

	s, err := net.Listen("unix", socketPath)
	if err != nil {
		glog.Errorf(errListenSocket+" %v", err)
		return err
	}

	m.wg.Add(1)
	m.server = grpc.NewServer([]grpc.ServerOption{}...)

	pluginapi.RegisterRegistrationServer(m.server, m)
	go func() {
		defer m.wg.Done()
		m.server.Serve(s)
	}()

	glog.V(2).Infof("Serving device plugin registration server on %q", socketPath)

	return nil
}

// GetWatcherHandler returns the plugin handler
func (m *ManagerImpl) GetWatcherHandler() watcher.PluginHandler {
	if f, err := os.Create(m.socketdir + "DEPRECATION"); err != nil {
		glog.Errorf("Failed to create deprecation file at %s", m.socketdir)
	} else {
		f.Close()
		glog.V(4).Infof("created deprecation file %s", f.Name())
	}

	return watcher.PluginHandler(m)
}

// ValidatePlugin validates a plugin if the version is correct and the name has the format of an extended resource
func (m *ManagerImpl) ValidatePlugin(pluginName string, endpoint string, versions []string) error {
	glog.V(2).Infof("Got Plugin %s at endpoint %s with versions %v", pluginName, endpoint, versions)

	if !m.isVersionCompatibleWithPlugin(versions) {
		return fmt.Errorf("manager version, %s, is not among plugin supported versions %v", pluginapi.Version, versions)
	}

	if !v1helper.IsExtendedResourceName(v1.ResourceName(pluginName)) {
		return fmt.Errorf("invalid name of device plugin socket: %s", fmt.Sprintf(errInvalidResourceName, pluginName))
	}

	return nil
}

// RegisterPlugin starts the endpoint and registers it
// TODO: Start the endpoint and wait for the First ListAndWatch call
//       before registering the plugin
func (m *ManagerImpl) RegisterPlugin(pluginName string, endpoint string) error {
	glog.V(2).Infof("Registering Plugin %s at endpoint %s", pluginName, endpoint)

	e, err := newEndpointImpl(endpoint, pluginName, m.callback)
	if err != nil {
		return fmt.Errorf("Failed to dial device plugin with socketPath %s: %v", endpoint, err)
	}

	options, err := e.client.GetDevicePluginOptions(context.Background(), &pluginapi.Empty{})
	if err != nil {
		return fmt.Errorf("Failed to get device plugin options: %v", err)
	}

	m.registerEndpoint(pluginName, options, e)
	go m.runEndpoint(pluginName, e)

	return nil
}

// DeRegisterPlugin deregisters the plugin
// TODO work on the behavior for deregistering plugins
// e.g: Should we delete the resource
func (m *ManagerImpl) DeRegisterPlugin(pluginName string) {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	// Note: This will mark the resource unhealthy as per the behavior
	// in runEndpoint
	if eI, ok := m.endpoints[pluginName]; ok {
		eI.e.stop()
	}
}

func (m *ManagerImpl) isVersionCompatibleWithPlugin(versions []string) bool {
	// TODO(vikasc): Currently this is fine as we only have a single supported version. When we do need to support
	// multiple versions in the future, we may need to extend this function to return a supported version.
	// E.g., say kubelet supports v1beta1 and v1beta2, and we get v1alpha1 and v1beta1 from a device plugin,
	// this function should return v1beta1
	for _, version := range versions {
		for _, supportedVersion := range pluginapi.SupportedVersions {
			if version == supportedVersion {
				return true
			}
		}
	}
	return false
}

// Allocate is the call that you can use to allocate a set of devices
// from the registered device plugins.
func (m *ManagerImpl) Allocate(node *schedulercache.NodeInfo, attrs *lifecycle.PodAdmitAttributes) error {
	pod := attrs.Pod
	devicesToReuse := make(map[string]sets.String)
	for _, container := range pod.Spec.InitContainers {
		if err := m.allocateContainerResources(pod, &container, devicesToReuse); err != nil {
			return err
		}
		m.podDevices.addContainerAllocatedResources(string(pod.UID), container.Name, devicesToReuse)
	}
	for _, container := range pod.Spec.Containers {
		if err := m.allocateContainerResources(pod, &container, devicesToReuse); err != nil {
			return err
		}
		m.podDevices.removeContainerAllocatedResources(string(pod.UID), container.Name, devicesToReuse)
	}

	m.mutex.Lock()
	defer m.mutex.Unlock()

	// quick return if no pluginResources requested
	if _, podRequireDevicePluginResource := m.podDevices[string(pod.UID)]; !podRequireDevicePluginResource {
		return nil
	}

	m.sanitizeNodeAllocatable(node)
	return nil
}

// Register registers a device plugin.
func (m *ManagerImpl) Register(ctx context.Context, r *pluginapi.RegisterRequest) (*pluginapi.Empty, error) {
	glog.Infof("Got registration request from device plugin with resource name %q", r.ResourceName)
	metrics.DevicePluginRegistrationCount.WithLabelValues(r.ResourceName).Inc()
	var versionCompatible bool
	for _, v := range pluginapi.SupportedVersions {
		if r.Version == v {
			versionCompatible = true
			break
		}
	}
	if !versionCompatible {
		errorString := fmt.Sprintf(errUnsupportedVersion, r.Version, pluginapi.SupportedVersions)
		glog.Infof("Bad registration request from device plugin with resource name %q: %s", r.ResourceName, errorString)
		return &pluginapi.Empty{}, fmt.Errorf(errorString)
	}

	if !v1helper.IsExtendedResourceName(v1.ResourceName(r.ResourceName)) {
		errorString := fmt.Sprintf(errInvalidResourceName, r.ResourceName)
		glog.Infof("Bad registration request from device plugin: %s", errorString)
		return &pluginapi.Empty{}, fmt.Errorf(errorString)
	}

	// TODO: for now, always accepts newest device plugin. Later may consider to
	// add some policies here, e.g., verify whether an old device plugin with the
	// same resource name is still alive to determine whether we want to accept
	// the new registration.
	go m.addEndpoint(r)

	return &pluginapi.Empty{}, nil
}

// Stop is the function that can stop the gRPC server.
// Can be called concurrently, more than once, and is safe to call
// without a prior Start.
func (m *ManagerImpl) Stop() error {
	m.mutex.Lock()
	defer m.mutex.Unlock()
	for _, eI := range m.endpoints {
		eI.e.stop()
	}

	if m.server == nil {
		return nil
	}
	m.server.Stop()
	m.wg.Wait()
	m.server = nil
	return nil
}

func (m *ManagerImpl) registerEndpoint(resourceName string, options *pluginapi.DevicePluginOptions, e endpoint) {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	m.endpoints[resourceName] = endpointInfo{e: e, opts: options}
	glog.V(2).Infof("Registered endpoint %v", e)
}

func (m *ManagerImpl) runEndpoint(resourceName string, e endpoint) {
	e.run()
	e.stop()

	m.mutex.Lock()
	defer m.mutex.Unlock()

	if old, ok := m.endpoints[resourceName]; ok && old.e == e {
		m.markResourceUnhealthy(resourceName)
	}

	glog.V(2).Infof("Endpoint (%s, %v) became unhealthy", resourceName, e)
}

func (m *ManagerImpl) addEndpoint(r *pluginapi.RegisterRequest) {
	new, err := newEndpointImpl(filepath.Join(m.socketdir, r.Endpoint), r.ResourceName, m.callback)
	if err != nil {
		glog.Errorf("Failed to dial device plugin with request %v: %v", r, err)
		return
	}
	m.registerEndpoint(r.ResourceName, r.Options, new)
	go func() {
		m.runEndpoint(r.ResourceName, new)
	}()
}

func (m *ManagerImpl) markResourceUnhealthy(resourceName string) {
	glog.V(2).Infof("Mark all resources Unhealthy for resource %s", resourceName)
	healthyDevices := sets.NewString()
	if _, ok := m.healthyDevices[resourceName]; ok {
		healthyDevices = m.healthyDevices[resourceName]
		m.healthyDevices[resourceName] = sets.NewString()
	}
	if _, ok := m.unhealthyDevices[resourceName]; !ok {
		m.unhealthyDevices[resourceName] = sets.NewString()
	}
	m.unhealthyDevices[resourceName] = m.unhealthyDevices[resourceName].Union(healthyDevices)
}

// GetCapacity is expected to be called when Kubelet updates its node status.
// The first returned variable contains the registered device plugin resource capacity.
// The second returned variable contains the registered device plugin resource allocatable.
// The third returned variable contains previously registered resources that are no longer active.
// Kubelet uses this information to update resource capacity/allocatable in its node status.
// After the call, device plugin can remove the inactive resources from its internal list as the
// change is already reflected in Kubelet node status.
// Note in the special case after Kubelet restarts, device plugin resource capacities can
// temporarily drop to zero till corresponding device plugins re-register. This is OK because
// cm.UpdatePluginResource() run during predicate Admit guarantees we adjust nodeinfo
// capacity for already allocated pods so that they can continue to run. However, new pods
// requiring device plugin resources will not be scheduled till device plugin re-registers.
func (m *ManagerImpl) GetCapacity() (v1.ResourceList, v1.ResourceList, []string) {
	needsUpdateCheckpoint := false
	var capacity = v1.ResourceList{}
	var allocatable = v1.ResourceList{}
	deletedResources := sets.NewString()
	m.mutex.Lock()
	for resourceName, devices := range m.healthyDevices {
		eI, ok := m.endpoints[resourceName]
		if (ok && eI.e.stopGracePeriodExpired()) || !ok {
			// The resources contained in endpoints and (un)healthyDevices
			// should always be consistent. Otherwise, we run with the risk
			// of failing to garbage collect non-existing resources or devices.
			if !ok {
				glog.Errorf("unexpected: healthyDevices and endpoints are out of sync")
			}
			delete(m.endpoints, resourceName)
			delete(m.healthyDevices, resourceName)
			deletedResources.Insert(resourceName)
			needsUpdateCheckpoint = true
		} else {
			capacity[v1.ResourceName(resourceName)] = *resource.NewQuantity(int64(devices.Len()), resource.DecimalSI)
			allocatable[v1.ResourceName(resourceName)] = *resource.NewQuantity(int64(devices.Len()), resource.DecimalSI)
		}
	}
	for resourceName, devices := range m.unhealthyDevices {
		eI, ok := m.endpoints[resourceName]
		if (ok && eI.e.stopGracePeriodExpired()) || !ok {
			if !ok {
				glog.Errorf("unexpected: unhealthyDevices and endpoints are out of sync")
			}
			delete(m.endpoints, resourceName)
			delete(m.unhealthyDevices, resourceName)
			deletedResources.Insert(resourceName)
			needsUpdateCheckpoint = true
		} else {
			capacityCount := capacity[v1.ResourceName(resourceName)]
			unhealthyCount := *resource.NewQuantity(int64(devices.Len()), resource.DecimalSI)
			capacityCount.Add(unhealthyCount)
			capacity[v1.ResourceName(resourceName)] = capacityCount
		}
	}
	m.mutex.Unlock()
	if needsUpdateCheckpoint {
		m.writeCheckpoint()
	}
	return capacity, allocatable, deletedResources.UnsortedList()
}

// Checkpoints device to container allocation information to disk.
func (m *ManagerImpl) writeCheckpoint() error {
	m.mutex.Lock()
	registeredDevs := make(map[string][]string)
	for resource, devices := range m.healthyDevices {
		registeredDevs[resource] = devices.UnsortedList()
	}
	data := checkpoint.New(m.podDevices.toCheckpointData(),
		registeredDevs)
	m.mutex.Unlock()
	err := m.checkpointManager.CreateCheckpoint(kubeletDeviceManagerCheckpoint, data)
	if err != nil {
		return fmt.Errorf("failed to write checkpoint file %q: %v", kubeletDeviceManagerCheckpoint, err)
	}
	return nil
}

// Reads device to container allocation information from disk, and populates
// m.allocatedDevices accordingly.
func (m *ManagerImpl) readCheckpoint() error {
	registeredDevs := make(map[string][]string)
	devEntries := make([]checkpoint.PodDevicesEntry, 0)
	cp := checkpoint.New(devEntries, registeredDevs)
	err := m.checkpointManager.GetCheckpoint(kubeletDeviceManagerCheckpoint, cp)
	if err != nil {
		if err == errors.ErrCheckpointNotFound {
			glog.Warningf("Failed to retrieve checkpoint for %q: %v", kubeletDeviceManagerCheckpoint, err)
			return nil
		}
		return err
	}
	m.mutex.Lock()
	defer m.mutex.Unlock()
	podDevices, registeredDevs := cp.GetData()
	m.podDevices.fromCheckpointData(podDevices)
	m.allocatedDevices = m.podDevices.devices()
	for resource := range registeredDevs {
		// During start up, creates empty healthyDevices list so that the resource capacity
		// will stay zero till the corresponding device plugin re-registers.
		m.healthyDevices[resource] = sets.NewString()
		m.unhealthyDevices[resource] = sets.NewString()
		m.endpoints[resource] = endpointInfo{e: newStoppedEndpointImpl(resource), opts: nil}
	}
	return nil
}

// updateAllocatedDevices gets a list of active pods and then frees any Devices that are bound to
// terminated pods. Returns error on failure.
func (m *ManagerImpl) updateAllocatedDevices(activePods []*v1.Pod) {
	if !m.sourcesReady.AllReady() {
		return
	}
	m.mutex.Lock()
	defer m.mutex.Unlock()
	activePodUids := sets.NewString()
	for _, pod := range activePods {
		activePodUids.Insert(string(pod.UID))
	}
	allocatedPodUids := m.podDevices.pods()
	podsToBeRemoved := allocatedPodUids.Difference(activePodUids)
	if len(podsToBeRemoved) <= 0 {
		return
	}
	glog.V(3).Infof("pods to be removed: %v", podsToBeRemoved.List())
	m.podDevices.delete(podsToBeRemoved.List())
	// Regenerated allocatedDevices after we update pod allocation information.
	m.allocatedDevices = m.podDevices.devices()
}

// Returns list of device Ids we need to allocate with Allocate rpc call.
// Returns empty list in case we don't need to issue the Allocate rpc call.
func (m *ManagerImpl) devicesToAllocate(podUID, contName, resource string, required int, reusableDevices sets.String) (sets.String, error) {
	m.mutex.Lock()
	defer m.mutex.Unlock()
	needed := required
	// Gets list of devices that have already been allocated.
	// This can happen if a container restarts for example.
	devices := m.podDevices.containerDevices(podUID, contName, resource)
	if devices != nil {
		glog.V(3).Infof("Found pre-allocated devices for resource %s container %q in Pod %q: %v", resource, contName, podUID, devices.List())
		needed = needed - devices.Len()
		// A pod's resource is not expected to change once admitted by the API server,
		// so just fail loudly here. We can revisit this part if this no longer holds.
		if needed != 0 {
			return nil, fmt.Errorf("pod %q container %q changed request for resource %q from %d to %d", podUID, contName, resource, devices.Len(), required)
		}
	}
	if needed == 0 {
		// No change, no work.
		return nil, nil
	}
	glog.V(3).Infof("Needs to allocate %d %q for pod %q container %q", needed, resource, podUID, contName)
	// Needs to allocate additional devices.
	if _, ok := m.healthyDevices[resource]; !ok {
		return nil, fmt.Errorf("can't allocate unregistered device %s", resource)
	}
	devices = sets.NewString()
	// Allocates from reusableDevices list first.
	for device := range reusableDevices {
		devices.Insert(device)
		needed--
		if needed == 0 {
			return devices, nil
		}
	}
	// Needs to allocate additional devices.
	if m.allocatedDevices[resource] == nil {
		m.allocatedDevices[resource] = sets.NewString()
	}
	// Gets Devices in use.
	devicesInUse := m.allocatedDevices[resource]
	// Gets a list of available devices.
	available := m.healthyDevices[resource].Difference(devicesInUse)
	if int(available.Len()) < needed {
		return nil, fmt.Errorf("requested number of devices unavailable for %s. Requested: %d, Available: %d", resource, needed, available.Len())
	}
	allocated := available.UnsortedList()[:needed]
	// Updates m.allocatedDevices with allocated devices to prevent them
	// from being allocated to other pods/containers, given that we are
	// not holding lock during the rpc call.
	for _, device := range allocated {
		m.allocatedDevices[resource].Insert(device)
		devices.Insert(device)
	}
	return devices, nil
}

// allocateContainerResources attempts to allocate all of required device
// plugin resources for the input container, issues an Allocate rpc request
// for each new device resource requirement, processes their AllocateResponses,
// and updates the cached containerDevices on success.
func (m *ManagerImpl) allocateContainerResources(pod *v1.Pod, container *v1.Container, devicesToReuse map[string]sets.String) error {
	podUID := string(pod.UID)
	contName := container.Name
	allocatedDevicesUpdated := false
	// Extended resources are not allowed to be overcommitted.
	// Since device plugin advertises extended resources,
	// therefore Requests must be equal to Limits and iterating
	// over the Limits should be sufficient.
	for k, v := range container.Resources.Limits {
		resource := string(k)
		needed := int(v.Value())
		glog.V(3).Infof("needs %d %s", needed, resource)
		if !m.isDevicePluginResource(resource) {
			continue
		}
		// Updates allocatedDevices to garbage collect any stranded resources
		// before doing the device plugin allocation.
		if !allocatedDevicesUpdated {
			m.updateAllocatedDevices(m.activePods())
			allocatedDevicesUpdated = true
		}
		allocDevices, err := m.devicesToAllocate(podUID, contName, resource, needed, devicesToReuse[resource])
		if err != nil {
			return err
		}
		if allocDevices == nil || len(allocDevices) <= 0 {
			continue
		}

		startRPCTime := time.Now()
		// Manager.Allocate involves RPC calls to device plugin, which
		// could be heavy-weight. Therefore we want to perform this operation outside
		// mutex lock. Note if Allocate call fails, we may leave container resources
		// partially allocated for the failed container. We rely on updateAllocatedDevices()
		// to garbage collect these resources later. Another side effect is that if
		// we have X resource A and Y resource B in total, and two containers, container1
		// and container2 both require X resource A and Y resource B. Both allocation
		// requests may fail if we serve them in mixed order.
		// TODO: may revisit this part later if we see inefficient resource allocation
		// in real use as the result of this. Should also consider to parallize device
		// plugin Allocate grpc calls if it becomes common that a container may require
		// resources from multiple device plugins.
		m.mutex.Lock()
		eI, ok := m.endpoints[resource]
		m.mutex.Unlock()
		if !ok {
			m.mutex.Lock()
			m.allocatedDevices = m.podDevices.devices()
			m.mutex.Unlock()
			return fmt.Errorf("Unknown Device Plugin %s", resource)
		}

		devs := allocDevices.UnsortedList()
		// TODO: refactor this part of code to just append a ContainerAllocationRequest
		// in a passed in AllocateRequest pointer, and issues a single Allocate call per pod.
		glog.V(3).Infof("Making allocation request for devices %v for device plugin %s", devs, resource)
		resp, err := eI.e.allocate(devs)
		metrics.DevicePluginAllocationLatency.WithLabelValues(resource).Observe(metrics.SinceInMicroseconds(startRPCTime))
		if err != nil {
			// In case of allocation failure, we want to restore m.allocatedDevices
			// to the actual allocated state from m.podDevices.
			m.mutex.Lock()
			m.allocatedDevices = m.podDevices.devices()
			m.mutex.Unlock()
			return err
		}

		if len(resp.ContainerResponses) == 0 {
			return fmt.Errorf("No containers return in allocation response %v", resp)
		}

		// Update internal cached podDevices state.
		m.mutex.Lock()
		m.podDevices.insert(podUID, contName, resource, allocDevices, resp.ContainerResponses[0])
		m.mutex.Unlock()
	}

	// Checkpoints device to container allocation information.
	return m.writeCheckpoint()
}

// GetDeviceRunContainerOptions checks whether we have cached containerDevices
// for the passed-in <pod, container> and returns its DeviceRunContainerOptions
// for the found one. An empty struct is returned in case no cached state is found.
func (m *ManagerImpl) GetDeviceRunContainerOptions(pod *v1.Pod, container *v1.Container) (*DeviceRunContainerOptions, error) {
	podUID := string(pod.UID)
	contName := container.Name
	for k := range container.Resources.Limits {
		resource := string(k)
		if !m.isDevicePluginResource(resource) {
			continue
		}
		err := m.callPreStartContainerIfNeeded(podUID, contName, resource)
		if err != nil {
			return nil, err
		}
	}
	m.mutex.Lock()
	defer m.mutex.Unlock()
	return m.podDevices.deviceRunContainerOptions(string(pod.UID), container.Name), nil
}

// callPreStartContainerIfNeeded issues PreStartContainer grpc call for device plugin resource
// with PreStartRequired option set.
func (m *ManagerImpl) callPreStartContainerIfNeeded(podUID, contName, resource string) error {
	m.mutex.Lock()
	eI, ok := m.endpoints[resource]
	if !ok {
		m.mutex.Unlock()
		return fmt.Errorf("endpoint not found in cache for a registered resource: %s", resource)
	}

	if eI.opts == nil || !eI.opts.PreStartRequired {
		m.mutex.Unlock()
		glog.V(4).Infof("Plugin options indicate to skip PreStartContainer for resource: %s", resource)
		return nil
	}

	devices := m.podDevices.containerDevices(podUID, contName, resource)
	if devices == nil {
		m.mutex.Unlock()
		return fmt.Errorf("no devices found allocated in local cache for pod %s, container %s, resource %s", podUID, contName, resource)
	}

	m.mutex.Unlock()
	devs := devices.UnsortedList()
	glog.V(4).Infof("Issuing an PreStartContainer call for container, %s, of pod %s", contName, podUID)
	_, err := eI.e.preStartContainer(devs)
	if err != nil {
		return fmt.Errorf("device plugin PreStartContainer rpc failed with err: %v", err)
	}
	// TODO: Add metrics support for init RPC
	return nil
}

// sanitizeNodeAllocatable scans through allocatedDevices in the device manager
// and if necessary, updates allocatableResource in nodeInfo to at least equal to
// the allocated capacity. This allows pods that have already been scheduled on
// the node to pass GeneralPredicates admission checking even upon device plugin failure.
func (m *ManagerImpl) sanitizeNodeAllocatable(node *schedulercache.NodeInfo) {
	var newAllocatableResource *schedulercache.Resource
	allocatableResource := node.AllocatableResource()
	if allocatableResource.ScalarResources == nil {
		allocatableResource.ScalarResources = make(map[v1.ResourceName]int64)
	}
	for resource, devices := range m.allocatedDevices {
		needed := devices.Len()
		quant, ok := allocatableResource.ScalarResources[v1.ResourceName(resource)]
		if ok && int(quant) >= needed {
			continue
		}
		// Needs to update nodeInfo.AllocatableResource to make sure
		// NodeInfo.allocatableResource at least equal to the capacity already allocated.
		if newAllocatableResource == nil {
			newAllocatableResource = allocatableResource.Clone()
		}
		newAllocatableResource.ScalarResources[v1.ResourceName(resource)] = int64(needed)
	}
	if newAllocatableResource != nil {
		node.SetAllocatableResource(newAllocatableResource)
	}
}

func (m *ManagerImpl) isDevicePluginResource(resource string) bool {
	_, registeredResource := m.healthyDevices[resource]
	_, allocatedResource := m.allocatedDevices[resource]
	// Return true if this is either an active device plugin resource or
	// a resource we have previously allocated.
	if registeredResource || allocatedResource {
		return true
	}
	return false
}