// +build windows
 

 // Maintainer:  jhowardmsft
 // Locale:      en-gb
 // About:       Graph-driver for Linux Containers On Windows (LCOW)
 //
 // This graphdriver runs in two modes. Yet to be determined which one will
 // be the shipping mode. The global mode is where a single utility VM
 // is used for all service VM tool operations. This isn't safe security-wise
 // as it's attaching a sandbox of multiple containers to it, containing
 // untrusted data. This may be fine for client devops scenarios. In
 // safe mode, a unique utility VM is instantiated for all service VM tool
 // operations. The downside of safe-mode is that operations are slower as
 // a new service utility VM has to be started and torn-down when needed.
 //
 // To enable global mode, run with --storage-opt lcow.globalmode=true
 
 // TODO: Grab logs from SVM at terminate or errors

 package lcow

 
 import (
 	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"

 	"strconv"

 	"strings"
 	"sync"
 	"time"
 

 	"github.com/Microsoft/hcsshim"

 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/docker/docker/pkg/archive"
 	"github.com/docker/docker/pkg/idtools"

 	"github.com/docker/docker/pkg/ioutils"

 	"github.com/docker/docker/pkg/system"
 	"github.com/jhowardmsft/opengcs/gogcs/client"

 	"github.com/sirupsen/logrus"

 )
 

 // init registers this driver to the register. It gets initialised by the
 // function passed in the second parameter, implemented in this file.

 func init() {

 	graphdriver.Register("lcow", InitDriver)

 }
 
 const (

 	// sandboxFilename is the name of the file containing a layer's sandbox (read-write layer).

 	sandboxFilename = "sandbox.vhdx"

 	// scratchFilename is the name of the scratch-space used by an SVM to avoid running out of memory.
 	scratchFilename = "scratch.vhdx"
 
 	// layerFilename is the name of the file containing a layer's read-only contents.
 	// Note this really is VHD format, not VHDX.
 	layerFilename = "layer.vhd"
 
 	// toolsScratchPath is a location in a service utility VM that the tools can use as a
 	// scratch space to avoid running out of memory.
 	// TODO @jhowardmsft. I really dislike this path! But needs a platform change or passing parameters to the tools.
 	toolsScratchPath = "/mnt/gcs/LinuxServiceVM/scratch"
 
 	// svmGlobalID is the ID used in the serviceVMs map for the global service VM when running in "global" mode.
 	svmGlobalID = "_lcow_global_svm_"
 
 	// cacheDirectory is the sub-folder under the driver's data-root used to cache blank sandbox and scratch VHDs.
 	cacheDirectory = "cache"
 
 	// scratchDirectory is the sub-folder under the driver's data-root used for scratch VHDs in service VMs
 	scratchDirectory = "scratch"

 )
 

 // cacheItem is our internal structure representing an item in our local cache

 // of things that have been mounted.

 type cacheItem struct {
 	sync.Mutex        // Protects operations performed on this item
 	uvmPath    string // Path in utility VM
 	hostPath   string // Path on host
 	refCount   int    // How many times its been mounted
 	isSandbox  bool   // True if a sandbox
 	isMounted  bool   // True when mounted in a service VM
 }
 
 // serviceVMItem is our internal structure representing an item in our
 // map of service VMs we are maintaining.
 type serviceVMItem struct {
 	sync.Mutex                     // Serialises operations being performed in this service VM.
 	scratchAttached bool           // Has a scratch been attached?
 	config          *client.Config // Represents the service VM item.

 }
 
 // Driver represents an LCOW graph driver.
 type Driver struct {

 	dataRoot           string                    // Root path on the host where we are storing everything.
 	cachedSandboxFile  string                    // Location of the local default-sized cached sandbox.
 	cachedSandboxMutex sync.Mutex                // Protects race conditions from multiple threads creating the cached sandbox.
 	cachedScratchFile  string                    // Location of the local cached empty scratch space.
 	cachedScratchMutex sync.Mutex                // Protects race conditions from multiple threads creating the cached scratch.
 	options            []string                  // Graphdriver options we are initialised with.
 	serviceVmsMutex    sync.Mutex                // Protects add/updates/delete to the serviceVMs map.
 	serviceVms         map[string]*serviceVMItem // Map of the configs representing the service VM(s) we are running.
 	globalMode         bool                      // Indicates if running in an unsafe/global service VM mode.
 
 	// NOTE: It is OK to use a cache here because Windows does not support

 	// restoring containers when the daemon dies.
 

 	cacheMutex sync.Mutex            // Protects add/update/deletes to cache.
 	cache      map[string]*cacheItem // Map holding a cache of all the IDs we've mounted/unmounted.

 }
 

 // deletefiles is a helper function for initialisation where we delete any
 // left-over scratch files in case we were previously forcibly terminated.
 func deletefiles(path string, f os.FileInfo, err error) error {
 	if strings.HasSuffix(f.Name(), ".vhdx") {
 		logrus.Warnf("lcowdriver: init: deleting stale scratch file %s", path)
 		return os.Remove(path)
 	}
 	return nil
 }
 
 // InitDriver returns a new LCOW storage driver.
 func InitDriver(dataRoot string, options []string, _, _ []idtools.IDMap) (graphdriver.Driver, error) {

 	title := "lcowdriver: init:"

 
 	cd := filepath.Join(dataRoot, cacheDirectory)
 	sd := filepath.Join(dataRoot, scratchDirectory)

 
 	d := &Driver{

 		dataRoot:          dataRoot,
 		options:           options,
 		cachedSandboxFile: filepath.Join(cd, sandboxFilename),
 		cachedScratchFile: filepath.Join(cd, scratchFilename),
 		cache:             make(map[string]*cacheItem),
 		serviceVms:        make(map[string]*serviceVMItem),
 		globalMode:        false,
 	}
 
 	// Looks for relevant options
 	for _, v := range options {
 		opt := strings.SplitN(v, "=", 2)
 		if len(opt) == 2 {
 			switch strings.ToLower(opt[0]) {
 			case "lcow.globalmode":
 				var err error
 				d.globalMode, err = strconv.ParseBool(opt[1])
 				if err != nil {
 					return nil, fmt.Errorf("%s failed to parse value for 'lcow.globalmode' - must be 'true' or 'false'", title)
 				}
 				break
 			}
 		}

 	}
 

 	// Make sure the dataRoot directory is created
 	if err := idtools.MkdirAllAs(dataRoot, 0700, 0, 0); err != nil {
 		return nil, fmt.Errorf("%s failed to create '%s': %v", title, dataRoot, err)

 	}
 

 	// Make sure the cache directory is created under dataRoot
 	if err := idtools.MkdirAllAs(cd, 0700, 0, 0); err != nil {
 		return nil, fmt.Errorf("%s failed to create '%s': %v", title, cd, err)

 	}
 

 	// Make sure the scratch directory is created under dataRoot
 	if err := idtools.MkdirAllAs(sd, 0700, 0, 0); err != nil {
 		return nil, fmt.Errorf("%s failed to create '%s': %v", title, sd, err)

 	}
 

 	// Delete any items in the scratch directory
 	filepath.Walk(sd, deletefiles)
 
 	logrus.Infof("%s dataRoot: %s globalMode: %t", title, dataRoot, d.globalMode)
 

 	return d, nil
 }
 

 // startServiceVMIfNotRunning starts a service utility VM if it is not currently running.
 // It can optionally be started with a mapped virtual disk. Returns a opengcs config structure
 // representing the VM.
 func (d *Driver) startServiceVMIfNotRunning(id string, mvdToAdd *hcsshim.MappedVirtualDisk, context string) (*serviceVMItem, error) {
 	// Use the global ID if in global mode
 	if d.globalMode {
 		id = svmGlobalID
 	}
 
 	title := fmt.Sprintf("lcowdriver: startservicevmifnotrunning %s:", id)

 	// Make sure thread-safe when interrogating the map
 	logrus.Debugf("%s taking serviceVmsMutex", title)
 	d.serviceVmsMutex.Lock()
 
 	// Nothing to do if it's already running except add the mapped drive if supplied.
 	if svm, ok := d.serviceVms[id]; ok {
 		logrus.Debugf("%s exists, releasing serviceVmsMutex", title)
 		d.serviceVmsMutex.Unlock()
 
 		if mvdToAdd != nil {
 			logrus.Debugf("hot-adding %s to %s", mvdToAdd.HostPath, mvdToAdd.ContainerPath)
 
 			// Ensure the item is locked while doing this
 			logrus.Debugf("%s locking serviceVmItem %s", title, svm.config.Name)
 			svm.Lock()
 
 			if err := svm.config.HotAddVhd(mvdToAdd.HostPath, mvdToAdd.ContainerPath); err != nil {
 				logrus.Debugf("%s releasing serviceVmItem %s on hot-add failure %s", title, svm.config.Name, err)
 				svm.Unlock()
 				return nil, fmt.Errorf("%s hot add %s to %s failed: %s", title, mvdToAdd.HostPath, mvdToAdd.ContainerPath, err)
 			}
 
 			logrus.Debugf("%s releasing serviceVmItem %s", title, svm.config.Name)
 			svm.Unlock()
 		}
 		return svm, nil
 	}
 
 	// Release the lock early
 	logrus.Debugf("%s releasing serviceVmsMutex", title)
 	d.serviceVmsMutex.Unlock()
 
 	// So we are starting one. First need an enpty structure.
 	svm := &serviceVMItem{
 		config: &client.Config{},

 	}
 

 	// Generate a default configuration
 	if err := svm.config.GenerateDefault(d.options); err != nil {
 		return nil, fmt.Errorf("%s failed to generate default gogcs configuration for global svm (%s): %s", title, context, err)

 	}
 

 	// For the name, we deliberately suffix if safe-mode to ensure that it doesn't
 	// clash with another utility VM which may be running for the container itself.
 	// This also makes it easier to correlate through Get-ComputeProcess.
 	if id == svmGlobalID {
 		svm.config.Name = svmGlobalID
 	} else {
 		svm.config.Name = fmt.Sprintf("%s_svm", id)
 	}
 
 	// Ensure we take the cached scratch mutex around the check to ensure the file is complete
 	// and not in the process of being created by another thread.
 	scratchTargetFile := filepath.Join(d.dataRoot, scratchDirectory, fmt.Sprintf("%s.vhdx", id))
 
 	logrus.Debugf("%s locking cachedScratchMutex", title)
 	d.cachedScratchMutex.Lock()
 	if _, err := os.Stat(d.cachedScratchFile); err == nil {
 		// Make a copy of cached scratch to the scratch directory
 		logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) cloning cached scratch for mvd", context)
 		if err := client.CopyFile(d.cachedScratchFile, scratchTargetFile, true); err != nil {
 			logrus.Debugf("%s releasing cachedScratchMutex on err: %s", title, err)
 			d.cachedScratchMutex.Unlock()
 			return nil, err
 		}
 
 		// Add the cached clone as a mapped virtual disk
 		logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) adding cloned scratch as mvd", context)

 		mvd := hcsshim.MappedVirtualDisk{

 			HostPath:          scratchTargetFile,

 			ContainerPath:     toolsScratchPath,
 			CreateInUtilityVM: true,
 		}

 		svm.config.MappedVirtualDisks = append(svm.config.MappedVirtualDisks, mvd)
 		svm.scratchAttached = true
 	}
 	logrus.Debugf("%s releasing cachedScratchMutex", title)
 	d.cachedScratchMutex.Unlock()
 
 	// If requested to start it with a mapped virtual disk, add it now.
 	if mvdToAdd != nil {
 		svm.config.MappedVirtualDisks = append(svm.config.MappedVirtualDisks, *mvdToAdd)
 	}
 
 	// Start it.
 	logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) starting %s", context, svm.config.Name)
 	if err := svm.config.Create(); err != nil {
 		return nil, fmt.Errorf("failed to start service utility VM (%s): %s", context, err)
 	}
 
 	// As it's now running, add it to the map, checking for a race where another
 	// thread has simultaneously tried to start it.
 	logrus.Debugf("%s locking serviceVmsMutex for insertion", title)
 	d.serviceVmsMutex.Lock()
 	if svm, ok := d.serviceVms[id]; ok {
 		logrus.Debugf("%s releasing serviceVmsMutex after insertion but exists", title)
 		d.serviceVmsMutex.Unlock()
 		return svm, nil
 	}
 	d.serviceVms[id] = svm
 	logrus.Debugf("%s releasing serviceVmsMutex after insertion", title)
 	d.serviceVmsMutex.Unlock()
 
 	// Now we have a running service VM, we can create the cached scratch file if it doesn't exist.
 	logrus.Debugf("%s locking cachedScratchMutex", title)
 	d.cachedScratchMutex.Lock()
 	if _, err := os.Stat(d.cachedScratchFile); err != nil {
 		// TODO: Not a typo, but needs fixing when the platform sandbox stuff has been sorted out.
 		logrus.Debugf("%s (%s): creating an SVM scratch - locking serviceVM", title, context)
 		svm.Lock()
 		if err := svm.config.CreateSandbox(d.cachedScratchFile, client.DefaultSandboxSizeMB, d.cachedSandboxFile); err != nil {
 			logrus.Debugf("%s (%s): releasing serviceVM on error path", title, context)
 			svm.Unlock()
 			logrus.Debugf("%s (%s): releasing cachedScratchMutex on error path", title, context)
 			d.cachedScratchMutex.Unlock()
 			// TODO: NEED TO REMOVE FROM MAP HERE AND STOP IT
 			return nil, fmt.Errorf("failed to create SVM scratch VHDX (%s): %s", context, err)
 		}
 		logrus.Debugf("%s (%s): releasing serviceVM on error path", title, context)
 		svm.Unlock()

 	}

 	logrus.Debugf("%s (%s): releasing cachedScratchMutex", title, context)
 	d.cachedScratchMutex.Unlock()

 
 	// Hot-add the scratch-space if not already attached

 	if !svm.scratchAttached {
 		// Make a copy of it to the layer directory
 		logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) cloning cached scratch for hot-add", context)
 		if err := client.CopyFile(d.cachedScratchFile, scratchTargetFile, true); err != nil {
 			// TODO: NEED TO REMOVE FROM MAP HERE AND STOP IT
 			return nil, err

 		}

 
 		logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) hot-adding scratch %s - locking serviceVM", context, scratchTargetFile)
 		svm.Lock()
 		if err := svm.config.HotAddVhd(scratchTargetFile, toolsScratchPath); err != nil {
 			logrus.Debugf("%s (%s): releasing serviceVM on error path", title, context)
 			svm.Unlock()
 			// TODOL NEED TO REMOVE FROM MAP HERE AND STOP IT
 			return nil, fmt.Errorf("failed to hot-add %s failed: %s", scratchTargetFile, err)

 		}

 		logrus.Debugf("%s (%s): releasing serviceVM", title, context)
 		svm.Unlock()

 	}

 
 	logrus.Debugf("lcowdriver: startServiceVmIfNotRunning: (%s) success", context)
 	return svm, nil

 }
 

 // getServiceVM returns the appropriate service utility VM instance, optionally
 // deleting it from the map (but not the global one)
 func (d *Driver) getServiceVM(id string, deleteFromMap bool) (*serviceVMItem, error) {
 	logrus.Debugf("lcowdriver: getservicevm:locking serviceVmsMutex")
 	d.serviceVmsMutex.Lock()
 	defer func() {
 		logrus.Debugf("lcowdriver: getservicevm:releasing serviceVmsMutex")
 		d.serviceVmsMutex.Unlock()
 	}()
 	if d.globalMode {
 		id = svmGlobalID
 	}
 	if _, ok := d.serviceVms[id]; !ok {
 		return nil, fmt.Errorf("getservicevm for %s failed as not found", id)
 	}
 	svm := d.serviceVms[id]
 	if deleteFromMap && id != svmGlobalID {
 		logrus.Debugf("lcowdriver: getservicevm: removing %s from map", id)
 		delete(d.serviceVms, id)
 	}
 	return svm, nil
 }
 
 // terminateServiceVM terminates a service utility VM if its running, but does nothing
 // when in global mode as it's lifetime is limited to that of the daemon.
 func (d *Driver) terminateServiceVM(id, context string, force bool) error {

 	// We don't do anything in safe mode unless the force flag has been passed, which
 	// is only the case for cleanup at driver termination.
 	if d.globalMode {
 		if !force {
 			logrus.Debugf("lcowdriver: terminateservicevm: %s (%s) - doing nothing as in global mode", id, context)
 			return nil
 		}
 		id = svmGlobalID
 	}

 	// Get the service VM and delete it from the map
 	svm, err := d.getServiceVM(id, true)
 	if err != nil {
 		return err

 	}
 

 	// We run the deletion of the scratch as a deferred function to at least attempt
 	// clean-up in case of errors.
 	defer func() {
 		if svm.scratchAttached {
 			scratchTargetFile := filepath.Join(d.dataRoot, scratchDirectory, fmt.Sprintf("%s.vhdx", id))
 			logrus.Debugf("lcowdriver: terminateservicevm: %s (%s) - deleting scratch %s", id, context, scratchTargetFile)
 			if err := os.Remove(scratchTargetFile); err != nil {
 				logrus.Warnf("failed to remove scratch file %s (%s): %s", scratchTargetFile, context, err)
 			}
 		}
 	}()
 
 	// Nothing to do if it's not running
 	if svm.config.Uvm != nil {
 		logrus.Debugf("lcowdriver: terminateservicevm: %s (%s) - calling terminate", id, context)
 		if err := svm.config.Uvm.Terminate(); err != nil {
 			return fmt.Errorf("failed to terminate utility VM (%s): %s", context, err)
 		}
 
 		logrus.Debugf("lcowdriver: terminateservicevm: %s (%s) - waiting for utility VM to terminate", id, context)
 		if err := svm.config.Uvm.WaitTimeout(time.Duration(svm.config.UvmTimeoutSeconds) * time.Second); err != nil {
 			return fmt.Errorf("failed waiting for utility VM to terminate (%s): %s", context, err)
 		}

 	}
 

 	logrus.Debugf("lcowdriver: terminateservicevm: %s (%s) - success", id, context)

 	return nil
 }
 
 // String returns the string representation of a driver. This should match
 // the name the graph driver has been registered with.
 func (d *Driver) String() string {
 	return "lcow"
 }
 
 // Status returns the status of the driver.
 func (d *Driver) Status() [][2]string {
 	return [][2]string{
 		{"LCOW", ""},

 		// TODO: Add some more info here - mode, home, ....

 	}
 }
 
 // Exists returns true if the given id is registered with this driver.
 func (d *Driver) Exists(id string) bool {
 	_, err := os.Lstat(d.dir(id))
 	logrus.Debugf("lcowdriver: exists: id %s %t", id, err == nil)
 	return err == nil
 }
 
 // CreateReadWrite creates a layer that is writable for use as a container

 // file system. That equates to creating a sandbox.

 func (d *Driver) CreateReadWrite(id, parent string, opts *graphdriver.CreateOpts) error {

 	title := fmt.Sprintf("lcowdriver: createreadwrite: id %s", id)
 	logrus.Debugf(title)

 	// First we need to create the folder
 	if err := d.Create(id, parent, opts); err != nil {

 		return err
 	}
 

 	// Massive perf optimisation here. If we know that the RW layer is the default size,
 	// and that the cached sandbox already exists, and we are running in safe mode, we
 	// can just do a simple copy into the layers sandbox file without needing to start a
 	// unique service VM. For a global service VM, it doesn't really matter.
 	//
 	// TODO: @jhowardmsft Where are we going to get the required size from?
 	// We need to look at the CreateOpts for that, I think....
 
 	// Make sure we have the sandbox mutex taken while we are examining it.
 	logrus.Debugf("%s: locking cachedSandboxMutex", title)
 	d.cachedSandboxMutex.Lock()
 	_, err := os.Stat(d.cachedSandboxFile)
 	logrus.Debugf("%s: releasing cachedSandboxMutex", title)
 	d.cachedSandboxMutex.Unlock()
 	if err == nil {
 		logrus.Debugf("%s: using cached sandbox to populate", title)
 		if err := client.CopyFile(d.cachedSandboxFile, filepath.Join(d.dir(id), sandboxFilename), true); err != nil {
 			return err
 		}
 		return nil
 	}
 
 	logrus.Debugf("%s: creating SVM to create sandbox", title)
 	svm, err := d.startServiceVMIfNotRunning(id, nil, "createreadwrite")
 	if err != nil {
 		return err
 	}
 	defer d.terminateServiceVM(id, "createreadwrite", false)
 
 	// So the cached sandbox needs creating. Ensure we are the only thread creating it.
 	logrus.Debugf("%s: locking cachedSandboxMutex for creation", title)
 	d.cachedSandboxMutex.Lock()
 	defer func() {
 		logrus.Debugf("%s: releasing cachedSandboxMutex for creation", title)
 		d.cachedSandboxMutex.Unlock()
 	}()
 
 	// Synchronise the operation in the service VM.
 	logrus.Debugf("%s: locking svm for sandbox creation", title)
 	svm.Lock()
 	defer func() {
 		logrus.Debugf("%s: releasing svm for sandbox creation", title)
 		svm.Unlock()
 	}()
 	if err := svm.config.CreateSandbox(filepath.Join(d.dir(id), sandboxFilename), client.DefaultSandboxSizeMB, d.cachedSandboxFile); err != nil {

 		return err
 	}
 

 	return nil

 }
 

 // Create creates the folder for the layer with the given id, and
 // adds it to the layer chain.

 func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
 	logrus.Debugf("lcowdriver: create: id %s parent: %s", id, parent)
 
 	parentChain, err := d.getLayerChain(parent)
 	if err != nil {
 		return err
 	}
 
 	var layerChain []string
 	if parent != "" {
 		if !d.Exists(parent) {

 			return fmt.Errorf("lcowdriver: cannot create layer folder with missing parent %s", parent)

 		}
 		layerChain = []string{d.dir(parent)}
 	}
 	layerChain = append(layerChain, parentChain...)
 
 	// Make sure layers are created with the correct ACL so that VMs can access them.
 	layerPath := d.dir(id)

 	logrus.Debugf("lcowdriver: create: id %s: creating %s", id, layerPath)

 	if err := system.MkdirAllWithACL(layerPath, 755, system.SddlNtvmAdministratorsLocalSystem); err != nil {
 		return err
 	}
 
 	if err := d.setLayerChain(id, layerChain); err != nil {
 		if err2 := os.RemoveAll(layerPath); err2 != nil {

 			logrus.Warnf("failed to remove layer %s: %s", layerPath, err2)

 		}
 		return err
 	}

 	logrus.Debugf("lcowdriver: create: id %s: success", id)

 
 	return nil
 }
 
 // Remove unmounts and removes the dir information.
 func (d *Driver) Remove(id string) error {
 	logrus.Debugf("lcowdriver: remove: id %s", id)
 	tmpID := fmt.Sprintf("%s-removing", id)
 	tmpLayerPath := d.dir(tmpID)
 	layerPath := d.dir(id)
 
 	logrus.Debugf("lcowdriver: remove: id %s: layerPath %s", id, layerPath)
 	if err := os.Rename(layerPath, tmpLayerPath); err != nil && !os.IsNotExist(err) {
 		return err
 	}
 
 	if err := os.RemoveAll(tmpLayerPath); err != nil {
 		return err
 	}
 
 	logrus.Debugf("lcowdriver: remove: id %s: layerPath %s succeeded", id, layerPath)
 	return nil
 }
 
 // Get returns the rootfs path for the id. It is reference counted and
 // effectively can be thought of as a "mount the layer into the utility

 // vm if it isn't already". The contract from the caller of this is that
 // all Gets and Puts are matched. It -should- be the case that on cleanup,
 // nothing is mounted.
 //
 // For optimisation, we don't actually mount the filesystem (which in our
 // case means [hot-]adding it to a service VM. But we track that and defer
 // the actual adding to the point we need to access it.

 func (d *Driver) Get(id, mountLabel string) (string, error) {

 	title := fmt.Sprintf("lcowdriver: get: %s", id)
 	logrus.Debugf(title)

 
 	// Work out what we are working on

 	vhdFilename, vhdSize, isSandbox, err := getLayerDetails(d.dir(id))

 	if err != nil {

 		logrus.Debugf("%s failed to get layer details from %s: %s", title, d.dir(id), err)
 		return "", fmt.Errorf("%s failed to open layer or sandbox VHD to open in %s: %s", title, d.dir(id), err)

 	}
 	logrus.Debugf("%s %s, size %d, isSandbox %t", title, vhdFilename, vhdSize, isSandbox)
 

 	// Add item to cache, or update existing item, but ensure we have the
 	// lock while updating items.
 	logrus.Debugf("%s: locking cacheMutex", title)
 	d.cacheMutex.Lock()
 	var cacheEntry *cacheItem
 	if entry, ok := d.cache[id]; !ok {

 		// The item is not currently in the cache.

 		cacheEntry = &cacheItem{

 			refCount:  1,
 			isSandbox: isSandbox,
 			hostPath:  vhdFilename,

 			uvmPath:   fmt.Sprintf("/mnt/%s", id),
 			isMounted: false, // we defer this as an optimisation

 		}

 		d.cache[id] = cacheEntry
 		logrus.Debugf("%s: added cache entry %+v", title, cacheEntry)

 	} else {
 		// Increment the reference counter in the cache.

 		logrus.Debugf("%s: locking cache item for increment", title)
 		entry.Lock()
 		entry.refCount++
 		logrus.Debugf("%s: releasing cache item for increment", title)
 		entry.Unlock()
 		logrus.Debugf("%s: incremented refcount on cache entry %+v", title, cacheEntry)

 	}

 	logrus.Debugf("%s: releasing cacheMutex", title)
 	d.cacheMutex.Unlock()

 
 	logrus.Debugf("%s %s success. %s: %+v: size %d", title, id, d.dir(id), cacheEntry, vhdSize)

 	return d.dir(id), nil

 }
 
 // Put does the reverse of get. If there are no more references to
 // the layer, it unmounts it from the utility VM.
 func (d *Driver) Put(id string) error {

 	title := fmt.Sprintf("lcowdriver: put: %s", id)

 	logrus.Debugf("%s: locking cacheMutex", title)
 	d.cacheMutex.Lock()

 	entry, ok := d.cache[id]
 	if !ok {

 		logrus.Debugf("%s: releasing cacheMutex on error path", title)
 		d.cacheMutex.Unlock()

 		return fmt.Errorf("%s possible ref-count error, or invalid id was passed to the graphdriver. Cannot handle id %s as it's not in the cache", title, id)
 	}
 

 	// Are we just decrementing the reference count?
 	logrus.Debugf("%s: locking cache item for possible decrement", title)
 	entry.Lock()

 	if entry.refCount > 1 {
 		entry.refCount--

 		logrus.Debugf("%s: releasing cache item for decrement and early get-out as refCount is now %d", title, entry.refCount)
 		entry.Unlock()
 		logrus.Debugf("%s: refCount decremented to %d. Releasing cacheMutex", title, entry.refCount)
 		d.cacheMutex.Unlock()

 		return nil
 	}

 	logrus.Debugf("%s: releasing cache item", title)
 	entry.Unlock()
 	logrus.Debugf("%s: releasing cacheMutex. Ref count has dropped to zero", title)
 	d.cacheMutex.Unlock()
 
 	// To reach this point, the reference count has dropped to zero. If we have
 	// done a mount and we are in global mode, then remove it. We don't
 	// need to remove in safe mode as the service VM is going to be torn down
 	// anyway.
 
 	if d.globalMode {
 		logrus.Debugf("%s: locking cache item at zero ref-count", title)
 		entry.Lock()
 		defer func() {
 			logrus.Debugf("%s: releasing cache item at zero ref-count", title)
 			entry.Unlock()
 		}()
 		if entry.isMounted {
 			svm, err := d.getServiceVM(id, false)
 			if err != nil {
 				return err
 			}

 			logrus.Debugf("%s: Hot-Removing %s. Locking svm", title, entry.hostPath)
 			svm.Lock()
 			if err := svm.config.HotRemoveVhd(entry.hostPath); err != nil {
 				logrus.Debugf("%s: releasing svm on error path", title)
 				svm.Unlock()
 				return fmt.Errorf("%s failed to hot-remove %s from global service utility VM: %s", title, entry.hostPath, err)
 			}
 			logrus.Debugf("%s: releasing svm", title)
 			svm.Unlock()

 		}
 	}
 
 	// Remove from the cache map.

 	logrus.Debugf("%s: Locking cacheMutex to delete item from cache", title)
 	d.cacheMutex.Lock()

 	delete(d.cache, id)

 	logrus.Debugf("%s: releasing cacheMutex after item deleted from cache", title)
 	d.cacheMutex.Unlock()

 
 	logrus.Debugf("%s %s: refCount 0. %s (%s) completed successfully", title, id, entry.hostPath, entry.uvmPath)
 	return nil
 }
 
 // Cleanup ensures the information the driver stores is properly removed.
 // We use this opportunity to cleanup any -removing folders which may be
 // still left if the daemon was killed while it was removing a layer.
 func (d *Driver) Cleanup() error {
 	title := "lcowdriver: cleanup"
 

 	d.cacheMutex.Lock()

 	for k, v := range d.cache {
 		logrus.Debugf("%s cache entry: %s: %+v", title, k, v)
 		if v.refCount > 0 {
 			logrus.Warnf("%s leaked %s: %+v", title, k, v)
 		}
 	}

 	d.cacheMutex.Unlock()

 	items, err := ioutil.ReadDir(d.dataRoot)

 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil
 		}
 		return err
 	}
 
 	// Note we don't return an error below - it's possible the files
 	// are locked. However, next time around after the daemon exits,
 	// we likely will be able to to cleanup successfully. Instead we log
 	// warnings if there are errors.
 	for _, item := range items {
 		if item.IsDir() && strings.HasSuffix(item.Name(), "-removing") {

 			if err := os.RemoveAll(filepath.Join(d.dataRoot, item.Name())); err != nil {

 				logrus.Warnf("%s failed to cleanup %s: %s", title, item.Name(), err)
 			} else {
 				logrus.Infof("%s cleaned up %s", title, item.Name())
 			}
 		}
 	}

 
 	// Cleanup any service VMs we have running, along with their scratch spaces.
 	// We don't take the lock for this as it's taken in terminateServiceVm.
 	for k, v := range d.serviceVms {
 		logrus.Debugf("%s svm entry: %s: %+v", title, k, v)
 		d.terminateServiceVM(k, "cleanup", true)
 	}
 

 	return nil
 }
 
 // Diff takes a layer (and it's parent layer which may be null, but
 // is ignored by this implementation below) and returns a reader for
 // a tarstream representing the layers contents. The id could be
 // a read-only "layer.vhd" or a read-write "sandbox.vhdx". The semantics
 // of this function dictate that the layer is already mounted.

 // However, as we do lazy mounting as a performance optimisation,
 // this will likely not be the case.

 func (d *Driver) Diff(id, parent string) (io.ReadCloser, error) {

 	title := fmt.Sprintf("lcowdriver: diff: %s", id)

 	logrus.Debugf("%s: locking cacheMutex", title)
 	d.cacheMutex.Lock()

 	if _, ok := d.cache[id]; !ok {

 		logrus.Debugf("%s: releasing cacheMutex on error path", title)
 		d.cacheMutex.Unlock()

 		return nil, fmt.Errorf("%s fail as %s is not in the cache", title, id)
 	}
 	cacheEntry := d.cache[id]

 	logrus.Debugf("%s: releasing cacheMutex", title)
 	d.cacheMutex.Unlock()

 
 	// Stat to get size

 	logrus.Debugf("%s: locking cacheEntry", title)
 	cacheEntry.Lock()

 	fileInfo, err := os.Stat(cacheEntry.hostPath)
 	if err != nil {

 		logrus.Debugf("%s: releasing cacheEntry on error path", title)
 		cacheEntry.Unlock()

 		return nil, fmt.Errorf("%s failed to stat %s: %s", title, cacheEntry.hostPath, err)
 	}

 	logrus.Debugf("%s: releasing cacheEntry", title)
 	cacheEntry.Unlock()

 	// Start the SVM with a mapped virtual disk. Note that if the SVM is
 	// already runing and we are in global mode, this will be
 	// hot-added.
 	mvd := &hcsshim.MappedVirtualDisk{
 		HostPath:          cacheEntry.hostPath,
 		ContainerPath:     cacheEntry.uvmPath,
 		CreateInUtilityVM: true,
 		ReadOnly:          true,
 	}
 
 	logrus.Debugf("%s: starting service VM", title)
 	svm, err := d.startServiceVMIfNotRunning(id, mvd, fmt.Sprintf("diff %s", id))
 	if err != nil {
 		return nil, err
 	}
 
 	// Set `isMounted` for the cache entry. Note that we re-scan the cache
 	// at this point as it's possible the cacheEntry changed during the long-
 	// running operation above when we weren't holding the cacheMutex lock.
 	logrus.Debugf("%s: locking cacheMutex for updating isMounted", title)
 	d.cacheMutex.Lock()
 	if _, ok := d.cache[id]; !ok {
 		logrus.Debugf("%s: releasing cacheMutex on error path of isMounted", title)
 		d.cacheMutex.Unlock()
 		d.terminateServiceVM(id, fmt.Sprintf("diff %s", id), false)
 		return nil, fmt.Errorf("%s fail as %s is not in the cache when updating isMounted", title, id)
 	}
 	cacheEntry = d.cache[id]
 	logrus.Debugf("%s: locking cacheEntry for updating isMounted", title)
 	cacheEntry.Lock()
 	cacheEntry.isMounted = true
 	logrus.Debugf("%s: releasing cacheEntry for updating isMounted", title)
 	cacheEntry.Unlock()
 	logrus.Debugf("%s: releasing cacheMutex for updating isMounted", title)
 	d.cacheMutex.Unlock()
 
 	// Obtain the tar stream for it

 	logrus.Debugf("%s %s, size %d, isSandbox %t", title, cacheEntry.hostPath, fileInfo.Size(), cacheEntry.isSandbox)

 	tarReadCloser, err := svm.config.VhdToTar(cacheEntry.hostPath, cacheEntry.uvmPath, cacheEntry.isSandbox, fileInfo.Size())

 	if err != nil {

 		d.terminateServiceVM(id, fmt.Sprintf("diff %s", id), false)

 		return nil, fmt.Errorf("%s failed to export layer to tar stream for id: %s, parent: %s : %s", title, id, parent, err)
 	}

 	logrus.Debugf("%s id %s parent %s completed successfully", title, id, parent)

 
 	// In safe/non-global mode, we can't tear down the service VM until things have been read.
 	if !d.globalMode {
 		return ioutils.NewReadCloserWrapper(tarReadCloser, func() error {
 			tarReadCloser.Close()
 			d.terminateServiceVM(id, fmt.Sprintf("diff %s", id), false)
 			return nil
 		}), nil
 	}

 	return tarReadCloser, nil
 }
 
 // ApplyDiff extracts the changeset from the given diff into the
 // layer with the specified id and parent, returning the size of the
 // new layer in bytes. The layer should not be mounted when calling
 // this function. Another way of describing this is that ApplyDiff writes
 // to a new layer (a VHD in LCOW) the contents of a tarstream it's given.
 func (d *Driver) ApplyDiff(id, parent string, diff io.Reader) (int64, error) {
 	logrus.Debugf("lcowdriver: applydiff: id %s", id)
 

 	svm, err := d.startServiceVMIfNotRunning(id, nil, fmt.Sprintf("applydiff %s", id))
 	if err != nil {

 		return 0, err
 	}

 	defer d.terminateServiceVM(id, fmt.Sprintf("applydiff %s", id), false)
 
 	// TODO @jhowardmsft - the retries are temporary to overcome platform reliablity issues.
 	// Obviously this will be removed as platform bugs are fixed.
 	retries := 0
 	for {
 		retries++
 		size, err := svm.config.TarToVhd(filepath.Join(d.dataRoot, id, layerFilename), diff)
 		if err != nil {
 			if retries <= 10 {
 				continue
 			}
 			return 0, err
 		}
 		return size, err
 	}

 }
 
 // Changes produces a list of changes between the specified layer
 // and its parent layer. If parent is "", then all changes will be ADD changes.
 // The layer should not be mounted when calling this function.
 func (d *Driver) Changes(id, parent string) ([]archive.Change, error) {
 	logrus.Debugf("lcowdriver: changes: id %s parent %s", id, parent)
 	// TODO @gupta-ak. Needs implementation with assistance from service VM
 	return nil, nil
 }
 
 // DiffSize calculates the changes between the specified layer
 // and its parent and returns the size in bytes of the changes
 // relative to its base filesystem directory.
 func (d *Driver) DiffSize(id, parent string) (size int64, err error) {
 	logrus.Debugf("lcowdriver: diffsize: id %s", id)
 	// TODO @gupta-ak. Needs implementation with assistance from service VM
 	return 0, nil
 }
 
 // GetMetadata returns custom driver information.
 func (d *Driver) GetMetadata(id string) (map[string]string, error) {
 	logrus.Debugf("lcowdriver: getmetadata: id %s", id)
 	m := make(map[string]string)
 	m["dir"] = d.dir(id)
 	return m, nil
 }
 
 // dir returns the absolute path to the layer.
 func (d *Driver) dir(id string) string {

 	return filepath.Join(d.dataRoot, filepath.Base(id))

 }
 
 // getLayerChain returns the layer chain information.
 func (d *Driver) getLayerChain(id string) ([]string, error) {
 	jPath := filepath.Join(d.dir(id), "layerchain.json")
 	logrus.Debugf("lcowdriver: getlayerchain: id %s json %s", id, jPath)
 	content, err := ioutil.ReadFile(jPath)
 	if os.IsNotExist(err) {
 		return nil, nil
 	} else if err != nil {
 		return nil, fmt.Errorf("lcowdriver: getlayerchain: %s unable to read layerchain file %s: %s", id, jPath, err)
 	}
 
 	var layerChain []string
 	err = json.Unmarshal(content, &layerChain)
 	if err != nil {
 		return nil, fmt.Errorf("lcowdriver: getlayerchain: %s failed to unmarshall layerchain file %s: %s", id, jPath, err)
 	}
 	return layerChain, nil
 }
 
 // setLayerChain stores the layer chain information on disk.
 func (d *Driver) setLayerChain(id string, chain []string) error {
 	content, err := json.Marshal(&chain)
 	if err != nil {
 		return fmt.Errorf("lcowdriver: setlayerchain: %s failed to marshall layerchain json: %s", id, err)
 	}
 
 	jPath := filepath.Join(d.dir(id), "layerchain.json")
 	logrus.Debugf("lcowdriver: setlayerchain: id %s json %s", id, jPath)
 	err = ioutil.WriteFile(jPath, content, 0600)
 	if err != nil {
 		return fmt.Errorf("lcowdriver: setlayerchain: %s failed to write layerchain file: %s", id, err)
 	}
 	return nil
 }

 
 // getLayerDetails is a utility for getting a file name, size and indication of
 // sandbox for a VHD(x) in a folder. A read-only layer will be layer.vhd. A
 // read-write layer will be sandbox.vhdx.
 func getLayerDetails(folder string) (string, int64, bool, error) {
 	var fileInfo os.FileInfo
 	isSandbox := false
 	filename := filepath.Join(folder, layerFilename)
 	var err error
 
 	if fileInfo, err = os.Stat(filename); err != nil {
 		filename = filepath.Join(folder, sandboxFilename)
 		if fileInfo, err = os.Stat(filename); err != nil {
 			if os.IsNotExist(err) {
 				return "", 0, isSandbox, fmt.Errorf("could not find layer or sandbox in %s", folder)
 			}
 			return "", 0, isSandbox, fmt.Errorf("error locating layer or sandbox in %s: %s", folder, err)
 		}
 		isSandbox = true
 	}
 	return filename, fileInfo.Size(), isSandbox, nil
 }