daemon/graphdriver/overlay/ fix lint errors/warnings

Addresses #14756
Signed-off-by: Srini Brahmaroutu <srbrahma@us.ibm.com>

daemon/graphdriver/overlay/copy.go

@@ -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

daemon/graphdriver/overlay/overlay.go

@@ -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

hack/make/validate-lint

@@ -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