// Register imports a pre-existing image into the graph.
// Returns nil if the image is already registered.
func (graph *Graph) Register(im image.Descriptor, layerData io.Reader) (err error) {
imgID := im.ID()
if err := image.ValidateID(imgID); 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(imgID)
defer graph.imageMutex.Unlock(imgID)
return graph.register(im, layerData)
}
func (graph *Graph) register(im image.Descriptor, layerData io.Reader) (err error) {
imgID := im.ID()
// Skip register if image is already registered
if graph.Exists(imgID) {
return nil
}
// The returned `error` must be named in this function's signature so that
// `err` is not shadowed in this deferred cleanup.
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.
if err != nil {
graph.driver.Remove(imgID)
}
}()
// 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(imgID)); 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(imgID)
tmp, err := graph.mktemp()
defer os.RemoveAll(tmp)
if err != nil {
return fmt.Errorf("mktemp failed: %s", err)
}
parent := im.Parent()
// Create root filesystem in the driver
if err := createRootFilesystemInDriver(graph, imgID, parent, layerData); err != nil {
return err
}
// Apply the diff/layer
config, err := im.MarshalConfig()
if err != nil {
return err
}
if err := graph.storeImage(imgID, parent, config, layerData, tmp); err != nil {
return err
}
// Commit
if err := os.Rename(tmp, graph.imageRoot(imgID)); err != nil {
return err
}
graph.idIndex.Add(imgID)
return nil
}