// Register imports a pre-existing image into the graph. func (graph *Graph) Register(img *image.Image, layerData archive.ArchiveReader) (err error) { if err := image.ValidateID(img.ID); err != nil { return err } // We need this entire operation to be atomic within the engine. Note that // this doesn't mean Register is fully safe yet. graph.imageMutex.Lock(img.ID) defer graph.imageMutex.Unlock(img.ID) defer func() { // If any error occurs, remove the new dir from the driver. // Don't check for errors since the dir might not have been created. // FIXME: this leaves a possible race condition. if err != nil { graph.driver.Remove(img.ID) } }() // (This is a convenience to save time. Race conditions are taken care of by os.Rename) if graph.Exists(img.ID) { return fmt.Errorf("Image %s already exists", img.ID) } // Ensure that the image root does not exist on the filesystem // when it is not registered in the graph. // This is common when you switch from one graph driver to another if err := os.RemoveAll(graph.ImageRoot(img.ID)); err != nil && !os.IsNotExist(err) { return err } // If the driver has this ID but the graph doesn't, remove it from the driver to start fresh. // (the graph is the source of truth). // Ignore errors, since we don't know if the driver correctly returns ErrNotExist. // (FIXME: make that mandatory for drivers). graph.driver.Remove(img.ID) tmp, err := graph.Mktemp("") defer os.RemoveAll(tmp) if err != nil { return fmt.Errorf("Mktemp failed: %s", err) } // Create root filesystem in the driver if err := graph.driver.Create(img.ID, img.Parent); err != nil { return fmt.Errorf("Driver %s failed to create image rootfs %s: %s", graph.driver, img.ID, err) } // Apply the diff/layer img.SetGraph(graph) if err := image.StoreImage(img, layerData, tmp); err != nil { return err } // Commit if err := os.Rename(tmp, graph.ImageRoot(img.ID)); err != nil { return err } graph.idIndex.Add(img.ID) return nil }