driver: simplify ApplyDiffFromStagingDirectory

enforce that the stagingDirectory must have the same value as the
diffOutput.Target variable.  It allows to simplify the internal API.

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

drivers/driver.go

@@ -249,8 +249,8 @@ type DriverWithDiffer interface {
 	// ApplyDiffWithDiffer applies the changes using the callback function.
 	// If id is empty, then a staging directory is created.  The staging directory is guaranteed to be usable with ApplyDiffFromStagingDirectory.
 	ApplyDiffWithDiffer(id, parent string, options *ApplyDiffWithDifferOpts, differ Differ) (output DriverWithDifferOutput, err error)
-	// ApplyDiffFromStagingDirectory applies the changes using the specified staging directory.
-	ApplyDiffFromStagingDirectory(id, parent, stagingDirectory string, diffOutput *DriverWithDifferOutput, options *ApplyDiffWithDifferOpts) error
+	// ApplyDiffFromStagingDirectory applies the changes using the diffOutput target directory.
+	ApplyDiffFromStagingDirectory(id, parent string, diffOutput *DriverWithDifferOutput, options *ApplyDiffWithDifferOpts) error
 	// CleanupStagingDirectory cleanups the staging directory.  It can be used to cleanup the staging directory on errors
 	CleanupStagingDirectory(stagingDirectory string) error
 	// DifferTarget gets the location where files are stored for the layer.

drivers/overlay/overlay.go

@@ -2124,7 +2124,8 @@ func (d *Driver) ApplyDiffWithDiffer(id, parent string, options *graphdriver.App
 }
 
 // ApplyDiffFromStagingDirectory applies the changes using the specified staging directory.
-func (d *Driver) ApplyDiffFromStagingDirectory(id, parent, stagingDirectory string, diffOutput *graphdriver.DriverWithDifferOutput, options *graphdriver.ApplyDiffWithDifferOpts) error {
+func (d *Driver) ApplyDiffFromStagingDirectory(id, parent string, diffOutput *graphdriver.DriverWithDifferOutput, options *graphdriver.ApplyDiffWithDifferOpts) error {
+	stagingDirectory := diffOutput.Target
 	if filepath.Dir(stagingDirectory) != d.getStagingDir() {
 		return fmt.Errorf("%q is not a staging directory", stagingDirectory)
 	}

layers.go

@@ -312,8 +312,8 @@ type rwLayerStore interface {
 	// CleanupStagingDirectory cleanups the staging directory.  It can be used to cleanup the staging directory on errors
 	CleanupStagingDirectory(stagingDirectory string) error
 
-	// ApplyDiffFromStagingDirectory uses stagingDirectory to create the diff.
-	ApplyDiffFromStagingDirectory(id, stagingDirectory string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error
+	// ApplyDiffFromStagingDirectory uses diffOutput.Target to create the diff.
+	ApplyDiffFromStagingDirectory(id string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error
 
 	// DifferTarget gets the location where files are stored for the layer.
 	DifferTarget(id string) (string, error)
@@ -2407,7 +2407,7 @@ func (r *layerStore) DifferTarget(id string) (string, error) {
 }
 
 // Requires startWriting.
-func (r *layerStore) ApplyDiffFromStagingDirectory(id, stagingDirectory string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error {
+func (r *layerStore) ApplyDiffFromStagingDirectory(id string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error {
 	ddriver, ok := r.driver.(drivers.DriverWithDiffer)
 	if !ok {
 		return ErrNotSupported
@@ -2426,7 +2426,7 @@ func (r *layerStore) ApplyDiffFromStagingDirectory(id, stagingDirectory string,
 		}
 	}
 
-	err := ddriver.ApplyDiffFromStagingDirectory(layer.ID, layer.Parent, stagingDirectory, diffOutput, options)
+	err := ddriver.ApplyDiffFromStagingDirectory(layer.ID, layer.Parent, diffOutput, options)
 	if err != nil {
 		return err
 	}

store.go

@@ -318,6 +318,7 @@ type Store interface {
 	ApplyDiffWithDiffer(to string, options *drivers.ApplyDiffWithDifferOpts, differ drivers.Differ) (*drivers.DriverWithDifferOutput, error)
 
 	// ApplyDiffFromStagingDirectory uses stagingDirectory to create the diff.
+	// Deprecated: it will be removed soon.
 	ApplyDiffFromStagingDirectory(to, stagingDirectory string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error
 
 	// CleanupStagingDirectory cleanups the staging directory.  It can be used to cleanup the staging directory on errors
@@ -2949,11 +2950,14 @@ func (s *store) Diff(from, to string, options *DiffOptions) (io.ReadCloser, erro
 }
 
 func (s *store) ApplyDiffFromStagingDirectory(to, stagingDirectory string, diffOutput *drivers.DriverWithDifferOutput, options *drivers.ApplyDiffWithDifferOpts) error {
+	if stagingDirectory != diffOutput.Target {
+		return fmt.Errorf("invalid value for staging directory, it must be the same as the differ target directory")
+	}
 	_, err := writeToLayerStore(s, func(rlstore rwLayerStore) (struct{}, error) {
 		if !rlstore.Exists(to) {
 			return struct{}{}, ErrLayerUnknown
 		}
-		return struct{}{}, rlstore.ApplyDiffFromStagingDirectory(to, stagingDirectory, diffOutput, options)
+		return struct{}{}, rlstore.ApplyDiffFromStagingDirectory(to, diffOutput, options)
 	})
 	return err
 }