@@ -12,10 +12,10 @@ import (

 	"github.com/docker/docker/pkg/system"

 )

-type CopyFlags int

+type copyFlags int

 const (

-	CopyHardlink CopyFlags = 1 << iota

+	copyHardlink copyFlags = 1 << iota

 )

 func copyRegular(srcPath, dstPath string, mode os.FileMode) error {

@@ -49,7 +49,7 @@ func copyXattr(srcPath, dstPath, attr string) error {

 	return nil

 }

-func copyDir(srcDir, dstDir string, flags CopyFlags) error {

+func copyDir(srcDir, dstDir string, flags copyFlags) error {

 	err := filepath.Walk(srcDir, func(srcPath string, f os.FileInfo, err error) error {

 		if err != nil {

 			return err

@@ -75,7 +75,7 @@ func copyDir(srcDir, dstDir string, flags CopyFlags) error {

 		switch f.Mode() & os.ModeType {

 		case 0: // Regular file

-			if flags&CopyHardlink != 0 {

+			if flags&copyHardlink != 0 {

 				isHardlink = true

 				if err := os.Link(srcPath, dstPath); err != nil {

 					return err

@@ -23,11 +23,15 @@ import (

 // implementation of ApplyDiff()

 var (

+	// ErrApplyDiffFallback is returned to indicate that a normal ApplyDiff is applied as a fallback from Naive diff writer.

 	ErrApplyDiffFallback = fmt.Errorf("Fall back to normal ApplyDiff")

 )

+// ApplyDiffProtoDriver wraps the ProtoDriver by extending the inteface with ApplyDiff method.

 type ApplyDiffProtoDriver interface {

 	graphdriver.ProtoDriver

+	// ApplyDiff writes the diff to the archive for the given id and parent id.

+	// It returns the size in bytes written if successful, an error ErrApplyDiffFallback is returned otherwise.

 	ApplyDiff(id, parent string, diff archive.Reader) (size int64, err error)

 }

@@ -36,6 +40,7 @@ type naiveDiffDriverWithApply struct {

 	applyDiff ApplyDiffProtoDriver

 }

+// NaiveDiffDriverWithApply returns a NaiveDiff driver with custom ApplyDiff.

 func NaiveDiffDriverWithApply(driver ApplyDiffProtoDriver) graphdriver.Driver {

 	return &naiveDiffDriverWithApply{

 		Driver:    graphdriver.NaiveDiffDriver(driver),

@@ -43,6 +48,7 @@ func NaiveDiffDriverWithApply(driver ApplyDiffProtoDriver) graphdriver.Driver {

 	}

 }

+// ApplyDiff creates a diff layer with either the NaiveDiffDriver or with a fallback.

 func (d *naiveDiffDriverWithApply) ApplyDiff(id, parent string, diff archive.Reader) (int64, error) {

 	b, err := d.applyDiff.ApplyDiff(id, parent, diff)

 	if err == ErrApplyDiffFallback {

@@ -79,11 +85,15 @@ func (d *naiveDiffDriverWithApply) ApplyDiff(id, parent string, diff archive.Rea

 // of that. This means all child images share file (but not directory)

 // data with the parent.

+// ActiveMount contains information about the count, path and whether is mounted or not.

+// This information is part of the Driver, that contains list of active mounts taht are part of this overlay.

 type ActiveMount struct {

 	count   int

 	path    string

 	mounted bool

 }

+

+// Driver contains information about the home directory and the list of active mounts that are created using this driver.

 type Driver struct {

 	home       string

 	sync.Mutex // Protects concurrent modification to active

@@ -96,6 +106,9 @@ func init() {

 	graphdriver.Register("overlay", Init)

 }

+// Init returns the NaiveDiffDriver, a native diff driver for overlay filesystem.

+// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.

+// If a overlay filesystem is not supported over a existing filesystem then error graphdriver.ErrIncompatibleFS is returned.

 func Init(home string, options []string) (graphdriver.Driver, error) {

 	if err := supportsOverlay(); err != nil {

@@ -161,12 +174,15 @@ func (d *Driver) String() string {

 	return "overlay"

 }

+// Status returns current driver information in a two dimensional string array.

+// Output contains "Backing Filesystem" used in this implementation.

 func (d *Driver) Status() [][2]string {

 	return [][2]string{

 		{"Backing Filesystem", backingFs},

 	}

 }

+// GetMetadata returns meta data about the overlay driver such as root, LowerDir, UpperDir, WorkDir and MergeDir used to store data.

 func (d *Driver) GetMetadata(id string) (map[string]string, error) {

 	dir := d.dir(id)

 	if _, err := os.Stat(dir); err != nil {

@@ -182,12 +198,12 @@ func (d *Driver) GetMetadata(id string) (map[string]string, error) {

 		return metadata, nil

 	}

-	lowerId, err := ioutil.ReadFile(path.Join(dir, "lower-id"))

+	lowerID, err := ioutil.ReadFile(path.Join(dir, "lower-id"))

 	if err != nil {

 		return nil, err

 	}

-	metadata["LowerDir"] = path.Join(d.dir(string(lowerId)), "root")

+	metadata["LowerDir"] = path.Join(d.dir(string(lowerID)), "root")

 	metadata["UpperDir"] = path.Join(dir, "upper")

 	metadata["WorkDir"] = path.Join(dir, "work")

 	metadata["MergedDir"] = path.Join(dir, "merged")

@@ -195,10 +211,14 @@ func (d *Driver) GetMetadata(id string) (map[string]string, error) {

 	return metadata, nil

 }

+// Cleanup simply returns nil and do not change the existing filesystem.

+// This is required to satisfy the graphdriver.Driver interface.

 func (d *Driver) Cleanup() error {

 	return nil

 }

+// Create is used to create the upper, lower, and merge directories required for overlay fs for a given id.

+// The parent filesystem is used to configure these directories for the overlay.

 func (d *Driver) Create(id string, parent string) (retErr error) {

 	dir := d.dir(id)

 	if err := os.MkdirAll(path.Dir(dir), 0700); err != nil {

@@ -251,12 +271,12 @@ func (d *Driver) Create(id string, parent string) (retErr error) {

 	// Otherwise, copy the upper and the lower-id from the parent

-	lowerId, err := ioutil.ReadFile(path.Join(parentDir, "lower-id"))

+	lowerID, err := ioutil.ReadFile(path.Join(parentDir, "lower-id"))

 	if err != nil {

 		return err

 	}

-	if err := ioutil.WriteFile(path.Join(dir, "lower-id"), lowerId, 0666); err != nil {

+	if err := ioutil.WriteFile(path.Join(dir, "lower-id"), lowerID, 0666); err != nil {

 		return err

 	}

@@ -284,6 +304,7 @@ func (d *Driver) dir(id string) string {

 	return path.Join(d.home, id)

 }

+// Remove cleans the directories that are created for this id.

 func (d *Driver) Remove(id string) error {

 	dir := d.dir(id)

 	if _, err := os.Stat(dir); err != nil {

@@ -292,6 +313,7 @@ func (d *Driver) Remove(id string) error {

 	return os.RemoveAll(dir)

 }

+// Get creates and mounts the required file system for the given id and returns the mount path.

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

 	// Protect the d.active from concurrent access

 	d.Lock()

@@ -318,11 +340,11 @@ func (d *Driver) Get(id string, mountLabel string) (string, error) {

 		return mount.path, nil

 	}

-	lowerId, err := ioutil.ReadFile(path.Join(dir, "lower-id"))

+	lowerID, err := ioutil.ReadFile(path.Join(dir, "lower-id"))

 	if err != nil {

 		return "", err

 	}

-	lowerDir := path.Join(d.dir(string(lowerId)), "root")

+	lowerDir := path.Join(d.dir(string(lowerID)), "root")

 	upperDir := path.Join(dir, "upper")

 	workDir := path.Join(dir, "work")

 	mergedDir := path.Join(dir, "merged")

@@ -338,6 +360,7 @@ func (d *Driver) Get(id string, mountLabel string) (string, error) {

 	return mount.path, nil

 }

+// Put unmounts the mount path created for the give id.

 func (d *Driver) Put(id string) error {

 	// Protect the d.active from concurrent access

 	d.Lock()

@@ -373,6 +396,7 @@ func (d *Driver) Put(id string) error {

 	return nil

 }

+// ApplyDiff applies the new layer on top of the root, if parent does not exist with will return a ErrApplyDiffFallback error.

 func (d *Driver) ApplyDiff(id string, parent string, diff archive.Reader) (size int64, err error) {

 	dir := d.dir(id)

@@ -407,7 +431,7 @@ func (d *Driver) ApplyDiff(id string, parent string, diff archive.Reader) (size

 		}

 	}()

-	if err = copyDir(parentRootDir, tmpRootDir, CopyHardlink); err != nil {

+	if err = copyDir(parentRootDir, tmpRootDir, copyHardlink); err != nil {

 		return 0, err

 	}

@@ -423,6 +447,7 @@ func (d *Driver) ApplyDiff(id string, parent string, diff archive.Reader) (size

 	return

 }

+// Exists checks to see if the id is already mounted.

 func (d *Driver) Exists(id string) bool {

 	_, err := os.Stat(d.dir(id))

 	return err == nil

@@ -27,6 +27,7 @@ packages=(

 	daemon/execdriver/windows

 	daemon/graphdriver/aufs

 	daemon/graphdriver/devmapper

+	daemon/graphdriver/overlay

 	daemon/graphdriver/vfs

 	daemon/graphdriver/zfs

 	daemon/logger