layer

Documentation

Overview

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.

Index

• Constants
• Variables
• func LogReleaseMetadata(metadatas []Metadata)
• func ReleaseAndLog(ls Store, l Layer)
• type ChainID
  • func CreateChainID(dgsts []DiffID) ChainID
  • func (id ChainID) String() string
• type DiffID
  • func (diffID DiffID) String() string
• type Layer
• type Metadata
• type MetadataStore
  • func NewFSMetadataStore(root string) (MetadataStore, error)
• type MetadataTransaction
• type MountInit
• type RWLayer
• type Store
  • func NewStore(store MetadataStore, driver graphdriver.Driver) (Store, error)
• type TarStreamer

Constants

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

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

Variables

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")

	// 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")
)

var EmptyLayer = &emptyLayer{}

EmptyLayer is a layer that corresponds to empty tar.

Functions

func LogReleaseMetadata

func LogReleaseMetadata(metadatas []Metadata)

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

func ReleaseAndLog

func ReleaseAndLog(ls Store, l Layer)

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

Types

type ChainID

type ChainID digest.Digest

ChainID is the content-addressable ID of a layer.

func CreateChainID

func CreateChainID(dgsts []DiffID) ChainID

CreateChainID returns ID for a layerDigest slice

func (ChainID) String

func (id ChainID) String() string

String returns a string rendition of a layer ID

type DiffID

type DiffID digest.Digest

DiffID is the hash of an individual layer tar.

func (DiffID) String

func (diffID DiffID) String() string

String returns a string rendition of a layer DiffID

type Layer

type Layer interface {
	TarStreamer

	// 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

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

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)
	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

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

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

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

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

type MountInit

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

type RWLayer interface {
	TarStreamer

	// Path returns the filesystem path to the writable
	// layer.
	Path() (string, error)

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

	// 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)
}

RWLayer represents a layer which is read and writable

type Store

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

	Mount(id string, parent ChainID, label string, init MountInit) (RWLayer, error)
	Unmount(id string) error
	DeleteMount(id string) ([]Metadata, error)
	Changes(id string) ([]archive.Change, error)
	Metadata(id string) (map[string]string, error)
}

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

func NewStore

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

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

type TarStreamer

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.