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 IsEmpty(diffID DiffID) bool
• func LogReleaseMetadata(metadatas []Metadata)
• func ReleaseAndLog(ls Store, l Layer)
• type ChainID
  • func CreateChainID(dgsts []DiffID) ChainID
  • func (id ChainID) String() string
• type CreateRWLayerOpts
• type DescribableStore
• type DiffID
  • func (diffID DiffID) String() string
• type Layer
• type Metadata
• type MountInit
• type RWLayer
• type Store
  • func NewStoreFromOptions(options StoreOptions) (Store, error)
• type StoreOptions
• 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")

	// 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")

	// 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 IsEmpty

func IsEmpty(diffID DiffID) bool

IsEmpty returns true if the layer is an EmptyLayer

func LogReleaseMetadata

func LogReleaseMetadata(metadatas []Metadata)

LogReleaseMetadata logs a metadata array, uses 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 CreateRWLayerOpts

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

CreateRWLayerOpts contains optional arguments to be passed to CreateRWLayer

type DescribableStore

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

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

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

	// 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

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

	// 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 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

	// 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
	// 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)

	// ApplyDiff applies the diff to the RW layer
	ApplyDiff(diff io.Reader) (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)
	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 NewStoreFromOptions

func NewStoreFromOptions(options StoreOptions) (Store, error)

NewStoreFromOptions creates a new Store instance

type StoreOptions

type StoreOptions struct {
	Root                      string
	MetadataStorePathTemplate string
	GraphDriver               string
	GraphDriverOptions        []string
	IDMapping                 idtools.IdentityMapping
	PluginGetter              plugingetter.PluginGetter
	ExperimentalEnabled       bool
}

StoreOptions are the options used to create a new Store instance

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.