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moby--moby/layer/mounted_layer.go

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package layer
import (
"io"
"sync"
"github.com/docker/docker/pkg/archive"
)
type mountedLayer struct {
name string
mountID string
initID string
parent *roLayer
path string
layerStore *layerStore
references map[RWLayer]*referencedRWLayer
}
func (ml *mountedLayer) cacheParent() string {
if ml.initID != "" {
return ml.initID
}
if ml.parent != nil {
return ml.parent.cacheID
}
return ""
}
func (ml *mountedLayer) TarStream() (io.ReadCloser, error) {
archiver, err := ml.layerStore.driver.Diff(ml.mountID, ml.cacheParent())
if err != nil {
return nil, err
}
return archiver, nil
}
func (ml *mountedLayer) Name() string {
return ml.name
}
func (ml *mountedLayer) Parent() Layer {
if ml.parent != nil {
return ml.parent
}
// Return a nil interface instead of an interface wrapping a nil
// pointer.
return nil
}
func (ml *mountedLayer) Mount(mountLabel string) (string, error) {
return ml.layerStore.driver.Get(ml.mountID, mountLabel)
}
func (ml *mountedLayer) Unmount() error {
return ml.layerStore.driver.Put(ml.mountID)
}
func (ml *mountedLayer) Size() (int64, error) {
return ml.layerStore.driver.DiffSize(ml.mountID, ml.cacheParent())
}
func (ml *mountedLayer) Changes() ([]archive.Change, error) {
return ml.layerStore.driver.Changes(ml.mountID, ml.cacheParent())
}
func (ml *mountedLayer) Metadata() (map[string]string, error) {
return ml.layerStore.driver.GetMetadata(ml.mountID)
}
func (ml *mountedLayer) getReference() RWLayer {
ref := &referencedRWLayer{
mountedLayer: ml,
}
ml.references[ref] = ref
return ref
}
func (ml *mountedLayer) hasReferences() bool {
return len(ml.references) > 0
}
func (ml *mountedLayer) incActivityCount(ref RWLayer) error {
rl, ok := ml.references[ref]
if !ok {
return ErrLayerNotRetained
}
if err := rl.acquire(); err != nil {
return err
}
return nil
}
func (ml *mountedLayer) deleteReference(ref RWLayer) error {
rl, ok := ml.references[ref]
if !ok {
return ErrLayerNotRetained
}
if err := rl.release(); err != nil {
return err
}
delete(ml.references, ref)
return nil
}
func (ml *mountedLayer) retakeReference(r RWLayer) {
if ref, ok := r.(*referencedRWLayer); ok {
ref.activityCount = 0
ml.references[ref] = ref
}
}
type referencedRWLayer struct {
*mountedLayer
activityL sync.Mutex
activityCount int
}
func (rl *referencedRWLayer) acquire() error {
rl.activityL.Lock()
defer rl.activityL.Unlock()
rl.activityCount++
return nil
}
func (rl *referencedRWLayer) release() error {
rl.activityL.Lock()
defer rl.activityL.Unlock()
if rl.activityCount > 0 {
return ErrActiveMount
}
rl.activityCount = -1
return nil
}
func (rl *referencedRWLayer) Mount(mountLabel string) (string, error) {
rl.activityL.Lock()
defer rl.activityL.Unlock()
if rl.activityCount == -1 {
return "", ErrLayerNotRetained
}
if rl.activityCount > 0 {
rl.activityCount++
return rl.path, nil
}
m, err := rl.mountedLayer.Mount(mountLabel)
if err == nil {
rl.activityCount++
rl.path = m
}
return m, err
}
// Unmount decrements the activity count and unmounts the underlying layer
// Callers should only call `Unmount` once per call to `Mount`, even on error.
func (rl *referencedRWLayer) Unmount() error {
rl.activityL.Lock()
defer rl.activityL.Unlock()
if rl.activityCount == 0 {
return ErrNotMounted
}
if rl.activityCount == -1 {
return ErrLayerNotRetained
}
rl.activityCount--
if rl.activityCount > 0 {
return nil
}
return rl.mountedLayer.Unmount()
}