package graphdriver import ( "fmt" "github.com/dotcloud/docker/archive" "github.com/dotcloud/docker/utils" "os" "path" ) type InitFunc func(root string) (Driver, error) type Driver interface { Create(id, parent string) error Remove(id string) error Get(id string) (dir string, err error) Diff(id string) (archive.Archive, error) DiffSize(id string) (bytes int64, err error) Cleanup() error } type Changer interface { Changes(id string) ([]archive.Change, error) } var ( // All registred drivers drivers map[string]InitFunc // Slice of drivers that should be used in an order priority = []string{ "aufs", "devicemapper", "dummy", } ) func init() { drivers = make(map[string]InitFunc) } 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 } func getDriver(name, home string) (Driver, error) { if initFunc, exists := drivers[name]; exists { return initFunc(path.Join(home, name)) } return nil, fmt.Errorf("No such driver: %s", name) } func New(root string) (Driver, error) { var driver Driver var lastError error // Use environment variable DOCKER_DRIVER to force a choice of driver if name := os.Getenv("DOCKER_DRIVER"); name != "" { return getDriver(name, root) } // Check for priority drivers first for _, name := range priority { driver, lastError = getDriver(name, root) if lastError != nil { utils.Debugf("Error loading driver %s: %s", name, lastError) continue } return driver, nil } // Check all registered drivers if no priority driver is found for _, initFunc := range drivers { driver, lastError = initFunc(root) if lastError != nil { continue } return driver, nil } return nil, lastError }