142 lines
4.4 KiB
Go
142 lines
4.4 KiB
Go
package graphdriver
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import (
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"errors"
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"fmt"
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"os"
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"path"
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"github.com/docker/docker/pkg/archive"
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)
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type FsMagic uint64
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const (
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FsMagicBtrfs = FsMagic(0x9123683E)
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FsMagicAufs = FsMagic(0x61756673)
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)
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type InitFunc func(root string, options []string) (Driver, error)
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// ProtoDriver defines the basic capabilities of a driver.
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// This interface exists solely to be a minimum set of methods
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// for client code which choose not to implement the entire Driver
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// interface and use the NaiveDiffDriver wrapper constructor.
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//
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// Use of ProtoDriver directly by client code is not recommended.
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type ProtoDriver interface {
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// String returns a string representation of this driver.
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String() string
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// Create creates a new, empty, filesystem layer with the
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// specified id and parent. Parent may be "".
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Create(id, parent string) error
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// Remove attempts to remove the filesystem layer with this id.
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Remove(id string) error
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// Get returns the mountpoint for the layered filesystem referred
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// to by this id. You can optionally specify a mountLabel or "".
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// Returns the absolute path to the mounted layered filesystem.
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Get(id, mountLabel string) (dir string, err error)
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// Put releases the system resources for the specified id,
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// e.g, unmounting layered filesystem.
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Put(id string)
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// Exists returns whether a filesystem layer with the specified
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// ID exists on this driver.
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Exists(id string) bool
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// Status returns a set of key-value pairs which give low
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// level diagnostic status about this driver.
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Status() [][2]string
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// Cleanup performs necessary tasks to release resources
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// held by the driver, e.g., unmounting all layered filesystems
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// known to this driver.
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Cleanup() error
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}
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// Driver is the interface for layered/snapshot file system drivers.
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type Driver interface {
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ProtoDriver
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// Diff produces an archive of the changes between the specified
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// layer and its parent layer which may be "".
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Diff(id, parent string) (archive.Archive, error)
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// Changes produces a list of changes between the specified layer
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// and its parent layer. If parent is "", then all changes will be ADD changes.
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Changes(id, parent string) ([]archive.Change, error)
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// ApplyDiff extracts the changeset from the given diff into the
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// layer with the specified id and parent, returning the size of the
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// new layer in bytes.
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ApplyDiff(id, parent string, diff archive.ArchiveReader) (bytes int64, err error)
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// DiffSize calculates the changes between the specified id
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// and its parent and returns the size in bytes of the changes
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// relative to its base filesystem directory.
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DiffSize(id, parent string) (bytes int64, err error)
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}
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var (
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DefaultDriver string
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// All registred drivers
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drivers map[string]InitFunc
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// Slice of drivers that should be used in an order
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priority = []string{
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"aufs",
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"btrfs",
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"devicemapper",
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"vfs",
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// experimental, has to be enabled manually for now
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"overlayfs",
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}
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ErrNotSupported = errors.New("driver not supported")
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ErrPrerequisites = errors.New("prerequisites for driver not satisfied (wrong filesystem?)")
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ErrIncompatibleFS = fmt.Errorf("backing file system is unsupported for this graph driver")
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)
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func init() {
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drivers = make(map[string]InitFunc)
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}
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func Register(name string, initFunc InitFunc) error {
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if _, exists := drivers[name]; exists {
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return fmt.Errorf("Name already registered %s", name)
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}
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drivers[name] = initFunc
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return nil
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}
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func GetDriver(name, home string, options []string) (Driver, error) {
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if initFunc, exists := drivers[name]; exists {
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return initFunc(path.Join(home, name), options)
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}
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return nil, ErrNotSupported
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}
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func New(root string, options []string) (driver Driver, err error) {
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for _, name := range []string{os.Getenv("DOCKER_DRIVER"), DefaultDriver} {
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if name != "" {
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return GetDriver(name, root, options)
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}
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}
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// Check for priority drivers first
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for _, name := range priority {
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driver, err = GetDriver(name, root, options)
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if err != nil {
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if err == ErrNotSupported || err == ErrPrerequisites || err == ErrIncompatibleFS {
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continue
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}
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return nil, err
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}
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return driver, nil
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}
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// Check all registered drivers if no priority driver is found
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for _, initFunc := range drivers {
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if driver, err = initFunc(root, options); err != nil {
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if err == ErrNotSupported || err == ErrPrerequisites || err == ErrIncompatibleFS {
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continue
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}
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return nil, err
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}
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return driver, nil
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}
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return nil, fmt.Errorf("No supported storage backend found")
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}
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