store: new API PutLayerFromStagingDirectory

Add a race-condition-free alternative to using CreateLayer and
ApplyDiffFromStagingDirectory, ensuring the store is locked for the
entire duration while the layer is being created and populated.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

store.go

@@ -71,6 +71,19 @@ type metadataStore interface {
 	rwMetadataStore
 }
 
+// PutLayerFromStagingDirectoryOptions contains options to pass to PutLayerFromStagingDirectory
+type PutLayerFromStagingDirectoryOptions struct {
+	ID           string        // Mandatory
+	ParentLayer  string        // Optional
+	Names        []string      // Optional
+	MountLabel   string        // Optional
+	Writeable    bool          // Optional
+	LayerOptions *LayerOptions // Optional
+
+	DiffOutput  *drivers.DriverWithDifferOutput  //Mandatory
+	DiffOptions *drivers.ApplyDiffWithDifferOpts //Mandatory
+}
+
 // An roBigDataStore wraps up the read-only big-data related methods of the
 // various types of file-based lookaside stores that we implement.
 type roBigDataStore interface {
@@ -321,6 +334,11 @@ type Store interface {
 	// Deprecated: it will be removed soon.
 	ApplyDiffFromStagingDirectory(to, stagingDirectory string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error
 
+	// PutLayerFromStagingDirectory combines the functions of CreateLayer and ApplyDiffFromStagingDirectory,
+	// marking the layer for automatic removal if applying the diff fails
+	// for any reason.
+	PutLayerFromStagingDirectory(args PutLayerFromStagingDirectoryOptions) (*Layer, error)
+
 	// CleanupStagingDirectory cleanups the staging directory.  It can be used to cleanup the staging directory on errors
 	CleanupStagingDirectory(stagingDirectory string) error
 
@@ -2962,6 +2980,35 @@ func (s *store) ApplyDiffFromStagingDirectory(to, stagingDirectory string, diffO
 	return err
 }
 
+func (s *store) PutLayerFromStagingDirectory(args PutLayerFromStagingDirectoryOptions) (*Layer, error) {
+	rlstore, rlstores, err := s.bothLayerStoreKinds()
+	if err != nil {
+		return nil, err
+	}
+	if err := rlstore.startWriting(); err != nil {
+		return nil, err
+	}
+	defer rlstore.stopWriting()
+	if err := s.containerStore.startWriting(); err != nil {
+		return nil, err
+	}
+	defer s.containerStore.stopWriting()
+
+	layer, _, err := s.putLayerLocked(rlstore, rlstores, args.ID, args.ParentLayer, args.Names, args.MountLabel, args.Writeable, args.LayerOptions, nil)
+	if err != nil {
+		return layer, err
+	}
+
+	if err := rlstore.ApplyDiffFromStagingDirectory(layer.ID, args.DiffOutput, args.DiffOptions); err != nil {
+		err2 := rlstore.Delete(layer.ID)
+		if err2 != nil {
+			err = multierror.Append(err, err2)
+		}
+		return nil, err
+	}
+	return layer, err
+}
+
 func (s *store) CleanupStagingDirectory(stagingDirectory string) error {
 	_, err := writeToLayerStore(s, func(rlstore rwLayerStore) (struct{}, error) {
 		return struct{}{}, rlstore.CleanupStagingDirectory(stagingDirectory)