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moby--moby/daemon/graphdriver/driver.go

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package graphdriver // import "github.com/docker/docker/daemon/graphdriver"
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import (
"fmt"
"io"
"os"
"path/filepath"
"strings"
"github.com/sirupsen/logrus"
"github.com/vbatts/tar-split/tar/storage"
"github.com/docker/docker/pkg/archive"
"github.com/docker/docker/pkg/containerfs"
"github.com/docker/docker/pkg/idtools"
"github.com/docker/docker/pkg/plugingetter"
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)
// FsMagic unsigned id of the filesystem in use.
type FsMagic uint32
const (
// FsMagicUnsupported is a predefined constant value other than a valid filesystem id.
FsMagicUnsupported = FsMagic(0x00000000)
)
var (
// All registered drivers
drivers map[string]InitFunc
)
//CreateOpts contains optional arguments for Create() and CreateReadWrite()
// methods.
type CreateOpts struct {
MountLabel string
StorageOpt map[string]string
}
// InitFunc initializes the storage driver.
type InitFunc func(root string, options []string, uidMaps, gidMaps []idtools.IDMap) (Driver, error)
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// ProtoDriver defines the basic capabilities of a driver.
// This interface exists solely to be a minimum set of methods
// for client code which choose not to implement the entire Driver
// interface and use the NaiveDiffDriver wrapper constructor.
//
// Use of ProtoDriver directly by client code is not recommended.
type ProtoDriver interface {
// String returns a string representation of this driver.
String() string
// CreateReadWrite creates a new, empty filesystem layer that is ready
// to be used as the storage for a container. Additional options can
// be passed in opts. parent may be "" and opts may be nil.
CreateReadWrite(id, parent string, opts *CreateOpts) error
// Create creates a new, empty, filesystem layer with the
// specified id and parent and options passed in opts. Parent
// may be "" and opts may be nil.
Create(id, parent string, opts *CreateOpts) error
// Remove attempts to remove the filesystem layer with this id.
Remove(id string) error
// Get returns the mountpoint for the layered filesystem referred
// to by this id. You can optionally specify a mountLabel or "".
// Returns the absolute path to the mounted layered filesystem.
Get(id, mountLabel string) (fs containerfs.ContainerFS, err error)
// Put releases the system resources for the specified id,
// e.g, unmounting layered filesystem.
Put(id string) error
// Exists returns whether a filesystem layer with the specified
// ID exists on this driver.
Exists(id string) bool
// Status returns a set of key-value pairs which give low
// level diagnostic status about this driver.
Status() [][2]string
// Returns a set of key-value pairs which give low level information
// about the image/container driver is managing.
GetMetadata(id string) (map[string]string, error)
// Cleanup performs necessary tasks to release resources
// held by the driver, e.g., unmounting all layered filesystems
// known to this driver.
Cleanup() error
}
// DiffDriver is the interface to use to implement graph diffs
type DiffDriver interface {
// Diff produces an archive of the changes between the specified
// layer and its parent layer which may be "".
Diff(id, parent string) (io.ReadCloser, error)
// Changes produces a list of changes between the specified layer
// and its parent layer. If parent is "", then all changes will be ADD changes.
Changes(id, parent string) ([]archive.Change, error)
// ApplyDiff extracts the changeset from the given diff into the
// layer with the specified id and parent, returning the size of the
// new layer in bytes.
// The archive.Reader must be an uncompressed stream.
ApplyDiff(id, parent string, diff io.Reader) (size int64, err error)
// DiffSize calculates the changes between the specified id
// and its parent and returns the size in bytes of the changes
// relative to its base filesystem directory.
DiffSize(id, parent string) (size int64, err error)
}
// Driver is the interface for layered/snapshot file system drivers.
type Driver interface {
ProtoDriver
DiffDriver
}
// Capabilities defines a list of capabilities a driver may implement.
// These capabilities are not required; however, they do determine how a
// graphdriver can be used.
type Capabilities struct {
// Flags that this driver is capable of reproducing exactly equivalent
// diffs for read-only layers. If set, clients can rely on the driver
// for consistent tar streams, and avoid extra processing to account
// for potential differences (eg: the layer store's use of tar-split).
ReproducesExactDiffs bool
}
// CapabilityDriver is the interface for layered file system drivers that
// can report on their Capabilities.
type CapabilityDriver interface {
Capabilities() Capabilities
}
// DiffGetterDriver is the interface for layered file system drivers that
// provide a specialized function for getting file contents for tar-split.
type DiffGetterDriver interface {
Driver
// DiffGetter returns an interface to efficiently retrieve the contents
// of files in a layer.
DiffGetter(id string) (FileGetCloser, error)
}
// FileGetCloser extends the storage.FileGetter interface with a Close method
// for cleaning up.
type FileGetCloser interface {
storage.FileGetter
// Close cleans up any resources associated with the FileGetCloser.
Close() error
}
// Checker makes checks on specified filesystems.
type Checker interface {
// IsMounted returns true if the provided path is mounted for the specific checker
IsMounted(path string) bool
}
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func init() {
drivers = make(map[string]InitFunc)
}
// Register registers an InitFunc for the driver.
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func Register(name string, initFunc InitFunc) error {
if _, exists := drivers[name]; exists {
return fmt.Errorf("Name already registered %s", name)
}
drivers[name] = initFunc
return nil
}
// GetDriver initializes and returns the registered driver
func GetDriver(name string, pg plugingetter.PluginGetter, config Options) (Driver, error) {
if initFunc, exists := drivers[name]; exists {
return initFunc(filepath.Join(config.Root, name), config.DriverOptions, config.UIDMaps, config.GIDMaps)
}
pluginDriver, err := lookupPlugin(name, pg, config)
if err == nil {
return pluginDriver, nil
}
logrus.WithError(err).WithField("driver", name).WithField("home-dir", config.Root).Error("Failed to GetDriver graph")
return nil, ErrNotSupported
}
// getBuiltinDriver initializes and returns the registered driver, but does not try to load from plugins
func getBuiltinDriver(name, home string, options []string, uidMaps, gidMaps []idtools.IDMap) (Driver, error) {
if initFunc, exists := drivers[name]; exists {
return initFunc(filepath.Join(home, name), options, uidMaps, gidMaps)
}
logrus.Errorf("Failed to built-in GetDriver graph %s %s", name, home)
return nil, ErrNotSupported
}
// Options is used to initialize a graphdriver
type Options struct {
Root string
DriverOptions []string
UIDMaps []idtools.IDMap
GIDMaps []idtools.IDMap
ExperimentalEnabled bool
}
// New creates the driver and initializes it at the specified root.
func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, error) {
if name != "" {
logrus.Debugf("[graphdriver] trying provided driver: %s", name) // so the logs show specified driver
return GetDriver(name, pg, config)
}
// Guess for prior driver
driversMap := scanPriorDrivers(config.Root)
list := strings.Split(priority, ",")
logrus.Debugf("[graphdriver] priority list: %v", list)
for _, name := range list {
if name == "vfs" {
// don't use vfs even if there is state present.
continue
}
if _, prior := driversMap[name]; prior {
// of the state found from prior drivers, check in order of our priority
// which we would prefer
driver, err := getBuiltinDriver(name, config.Root, config.DriverOptions, config.UIDMaps, config.GIDMaps)
if err != nil {
// unlike below, we will return error here, because there is prior
// state, and now it is no longer supported/prereq/compatible, so
// something changed and needs attention. Otherwise the daemon's
// images would just "disappear".
logrus.Errorf("[graphdriver] prior storage driver %s failed: %s", name, err)
return nil, err
}
// abort starting when there are other prior configured drivers
// to ensure the user explicitly selects the driver to load
if len(driversMap)-1 > 0 {
var driversSlice []string
for name := range driversMap {
driversSlice = append(driversSlice, name)
}
return nil, fmt.Errorf("%s contains several valid graphdrivers: %s; Please cleanup or explicitly choose storage driver (-s <DRIVER>)", config.Root, strings.Join(driversSlice, ", "))
}
logrus.Infof("[graphdriver] using prior storage driver: %s", name)
return driver, nil
}
}
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// Check for priority drivers first
for _, name := range list {
driver, err := getBuiltinDriver(name, config.Root, config.DriverOptions, config.UIDMaps, config.GIDMaps)
if err != nil {
if IsDriverNotSupported(err) {
continue
}
return nil, err
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}
return driver, nil
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}
// Check all registered drivers if no priority driver is found
for name, initFunc := range drivers {
driver, err := initFunc(filepath.Join(config.Root, name), config.DriverOptions, config.UIDMaps, config.GIDMaps)
if err != nil {
if IsDriverNotSupported(err) {
continue
}
return nil, err
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}
return driver, nil
}
return nil, fmt.Errorf("No supported storage backend found")
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}
// scanPriorDrivers returns an un-ordered scan of directories of prior storage drivers
func scanPriorDrivers(root string) map[string]bool {
driversMap := make(map[string]bool)
for driver := range drivers {
p := filepath.Join(root, driver)
if _, err := os.Stat(p); err == nil && driver != "vfs" {
if !isEmptyDir(p) {
driversMap[driver] = true
}
}
}
return driversMap
}
// IsInitialized checks if the driver's home-directory exists and is non-empty.
func IsInitialized(driverHome string) bool {
_, err := os.Stat(driverHome)
if os.IsNotExist(err) {
return false
}
if err != nil {
logrus.Warnf("graphdriver.IsInitialized: stat failed: %v", err)
}
return !isEmptyDir(driverHome)
}
// isEmptyDir checks if a directory is empty. It is used to check if prior
// storage-driver directories exist. If an error occurs, it also assumes the
// directory is not empty (which preserves the behavior _before_ this check
// was added)
func isEmptyDir(name string) bool {
f, err := os.Open(name)
if err != nil {
return false
}
defer f.Close()
if _, err = f.Readdirnames(1); err == io.EOF {
return true
}
return false
}