Documentation
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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 ¶
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") // 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 ¶
ReleaseAndLog releases the provided layer from the given layer store, logging any error and release metadata
Types ¶
type ChainID ¶
ChainID is the content-addressable ID of a layer.
func CreateChainID ¶
CreateChainID returns ID for a layerDigest slice
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(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 ¶
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
// 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 ¶
type Store interface {
Register(io.Reader, ChainID) (Layer, error)
Get(ChainID) (Layer, error)
Release(Layer) ([]Metadata, error)
CreateRWLayer(id string, parent ChainID, mountLabel string, initFunc MountInit) (RWLayer, error)
GetRWLayer(id string) (RWLayer, 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 ¶
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 ¶
func NewStoreFromOptions(options StoreOptions) (Store, error)
NewStoreFromOptions creates a new Store instance
type StoreOptions ¶
type StoreOptions struct {
StorePath string
MetadataStorePathTemplate string
GraphDriver string
GraphDriverOptions []string
UIDMaps []idtools.IDMap
GIDMaps []idtools.IDMap
}
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.
Source Files