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package layer

import ""

Package layer is package for managing read-only and read-write mounts on the union file system driver. Read-only mounts are referenced using a content hash and are protected from mutation in the exposed interface. The tar format is used to create read-only layers and export both read-only and writable layers. The exported tar data for a read-only layer should match the tar used to create the layer.


Package Files

empty.go filestore.go layer.go layer_store.go layer_unix.go migration.go mounted_layer.go ro_layer.go


const DigestSHA256EmptyTar = DiffID("sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef")

DigestSHA256EmptyTar is the canonical sha256 digest of empty tar file - (1024 NULL bytes)


var (
    // ErrLayerDoesNotExist is used when an operation is
    // attempted on a layer which does not exist.
    ErrLayerDoesNotExist = errors.New("layer does not exist")

    // ErrLayerNotRetained is used when a release is
    // attempted on a layer which is not retained.
    ErrLayerNotRetained = errors.New("layer not retained")

    // ErrMountDoesNotExist is used when an operation is
    // attempted on a mount layer which does not exist.
    ErrMountDoesNotExist = errors.New("mount does not exist")

    // ErrMountNameConflict is used when a mount is attempted
    // to be created but there is already a mount with the name
    // used for creation.
    ErrMountNameConflict = errors.New("mount already exists with name")

    // ErrActiveMount is used when an operation on a
    // mount is attempted but the layer is still
    // mounted and the operation cannot be performed.
    ErrActiveMount = errors.New("mount still active")

    // ErrNotMounted is used when requesting an active
    // mount but the layer is not mounted.
    ErrNotMounted = errors.New("not mounted")

    // ErrMaxDepthExceeded is used when a layer is attempted
    // to be created which would result in a layer depth
    // greater than the 125 max.
    ErrMaxDepthExceeded = errors.New("max depth exceeded")

    // ErrNotSupported is used when the action is not supported
    // on the current platform
    ErrNotSupported = errors.New("not support on this platform")
var EmptyLayer = &emptyLayer{}

EmptyLayer is a layer that corresponds to empty tar.

func LogReleaseMetadata Uses

func LogReleaseMetadata(metadatas []Metadata)

LogReleaseMetadata logs a metadata array, uses this to ensure consistent logging for release metadata

func ReleaseAndLog Uses

func ReleaseAndLog(ls Store, l Layer)

ReleaseAndLog releases the provided layer from the given layer store, logging any error and release metadata

type ChainID Uses

type ChainID digest.Digest

ChainID is the content-addressable ID of a layer.

func CreateChainID Uses

func CreateChainID(dgsts []DiffID) ChainID

CreateChainID returns ID for a layerDigest slice

func (ChainID) String Uses

func (id ChainID) String() string

String returns a string rendition of a layer ID

type CreateRWLayerOpts Uses

type CreateRWLayerOpts struct {
    MountLabel string
    InitFunc   MountInit
    StorageOpt map[string]string

CreateRWLayerOpts contains optional arguments to be passed to CreateRWLayer

type DescribableStore Uses

type DescribableStore interface {
    RegisterWithDescriptor(io.Reader, ChainID, distribution.Descriptor) (Layer, error)

DescribableStore represents a layer store capable of storing descriptors for layers.

type DiffID Uses

type DiffID digest.Digest

DiffID is the hash of an individual layer tar.

func (DiffID) String Uses

func (diffID DiffID) String() string

String returns a string rendition of a layer DiffID

type Layer Uses

type Layer interface {

    // TarStreamFrom returns a tar archive stream for all the layer chain with
    // arbitrary depth.
    TarStreamFrom(ChainID) (io.ReadCloser, error)

    // ChainID returns the content hash of the entire layer chain. The hash
    // chain is made up of DiffID of top layer and all of its parents.
    ChainID() ChainID

    // DiffID returns the content hash of the layer
    // tar stream used to create this layer.
    DiffID() DiffID

    // Parent returns the next layer in the layer chain.
    Parent() Layer

    // Size returns the size of the entire layer chain. The size
    // is calculated from the total size of all files in the layers.
    Size() (int64, error)

    // DiffSize returns the size difference of the top layer
    // from parent layer.
    DiffSize() (int64, error)

    // Metadata returns the low level storage metadata associated
    // with layer.
    Metadata() (map[string]string, error)

Layer represents a read-only layer

type Metadata Uses

type Metadata struct {
    // ChainID is the content hash of the layer
    ChainID ChainID

    // DiffID is the hash of the tar data used to
    // create the layer
    DiffID DiffID

    // Size is the size of the layer and all parents
    Size int64

    // DiffSize is the size of the top layer
    DiffSize int64

Metadata holds information about a read-only layer

type MetadataStore Uses

type MetadataStore interface {
    // StartTransaction starts an update for new metadata
    // which will be used to represent an ID on commit.
    StartTransaction() (MetadataTransaction, error)

    GetSize(ChainID) (int64, error)
    GetParent(ChainID) (ChainID, error)
    GetDiffID(ChainID) (DiffID, error)
    GetCacheID(ChainID) (string, error)
    GetDescriptor(ChainID) (distribution.Descriptor, error)
    TarSplitReader(ChainID) (io.ReadCloser, error)

    SetMountID(string, string) error
    SetInitID(string, string) error
    SetMountParent(string, ChainID) error

    GetMountID(string) (string, error)
    GetInitID(string) (string, error)
    GetMountParent(string) (ChainID, error)

    // List returns the full list of referenced
    // read-only and read-write layers
    List() ([]ChainID, []string, error)

    Remove(ChainID) error
    RemoveMount(string) error

MetadataStore represents a backend for persisting metadata about layers and providing the metadata for restoring a Store.

func NewFSMetadataStore Uses

func NewFSMetadataStore(root string) (MetadataStore, error)

NewFSMetadataStore returns an instance of a metadata store which is backed by files on disk using the provided root as the root of metadata files.

type MetadataTransaction Uses

type MetadataTransaction interface {
    SetSize(int64) error
    SetParent(parent ChainID) error
    SetDiffID(DiffID) error
    SetCacheID(string) error
    SetDescriptor(distribution.Descriptor) error
    TarSplitWriter(compressInput bool) (io.WriteCloser, error)

    Commit(ChainID) error
    Cancel() error
    String() string

MetadataTransaction represents functions for setting layer metadata with a single transaction.

type MountInit Uses

type MountInit func(root string) error

MountInit is a function to initialize a writable mount. Changes made here will not be included in the Tar stream of the RWLayer.

type RWLayer Uses

type RWLayer interface {

    // Name of mounted layer
    Name() string

    // Parent returns the layer which the writable
    // layer was created from.
    Parent() Layer

    // Mount mounts the RWLayer and returns the filesystem path
    // the to the writable layer.
    Mount(mountLabel string) (string, error)

    // Unmount unmounts the RWLayer. This should be called
    // for every mount. If there are multiple mount calls
    // this operation will only decrement the internal mount counter.
    Unmount() error

    // Size represents the size of the writable layer
    // as calculated by the total size of the files
    // changed in the mutable layer.
    Size() (int64, error)

    // Changes returns the set of changes for the mutable layer
    // from the base layer.
    Changes() ([]archive.Change, error)

    // Metadata returns the low level metadata for the mutable layer
    Metadata() (map[string]string, error)

RWLayer represents a layer which is read and writable

type Store Uses

type Store interface {
    Register(io.Reader, ChainID) (Layer, error)
    Get(ChainID) (Layer, error)
    Map() map[ChainID]Layer
    Release(Layer) ([]Metadata, error)

    CreateRWLayer(id string, parent ChainID, opts *CreateRWLayerOpts) (RWLayer, error)
    GetRWLayer(id string) (RWLayer, error)
    GetMountID(id string) (string, error)
    ReleaseRWLayer(RWLayer) ([]Metadata, error)

    Cleanup() error
    DriverStatus() [][2]string
    DriverName() string

Store represents a backend for managing both read-only and read-write layers.

func NewStoreFromGraphDriver Uses

func NewStoreFromGraphDriver(store MetadataStore, driver graphdriver.Driver) (Store, error)

NewStoreFromGraphDriver creates a new Store instance using the provided metadata store and graph driver. The metadata store will be used to restore the Store.

func NewStoreFromOptions Uses

func NewStoreFromOptions(options StoreOptions) (Store, error)

NewStoreFromOptions creates a new Store instance

type StoreOptions Uses

type StoreOptions struct {
    StorePath                 string
    MetadataStorePathTemplate string
    GraphDriver               string
    GraphDriverOptions        []string
    UIDMaps                   []idtools.IDMap
    GIDMaps                   []idtools.IDMap
    PluginGetter              plugingetter.PluginGetter
    ExperimentalEnabled       bool

StoreOptions are the options used to create a new Store instance

type TarStreamer Uses

type TarStreamer interface {
    // TarStream returns a tar archive stream
    // for the contents of a layer.
    TarStream() (io.ReadCloser, error)

TarStreamer represents an object which may have its contents exported as a tar stream.

Package layer imports 25 packages (graph). Updated 2019-08-23. Refresh now. Tools for package owners.