Update out-of-date comments

Should not change behavior.

Signed-off-by: Miloslav Trmač <[email protected]>

storage/storage_src.go

@@ -122,8 +122,9 @@ func (s *storageImageSource) GetBlob(ctx context.Context, info types.BlobInfo, c
 
 	var layers []storage.Layer
 
-	// If the digest was overridden by LayerInfosForCopy, then we need to use the TOC digest
-	// to retrieve it from the storage.
+	// This lookup path is strictly necessary for layers identified by TOC digest
+	// (where LayersByUncompressedDigest might not find our layer);
+	// for other layers it is an optimization to avoid the cost of the LayersByUncompressedDigest call.
 	s.getBlobMutex.Lock()
 	layerID, found := s.getBlobMutexProtected.digestToLayerID[digest]
 	s.getBlobMutex.Unlock()
@@ -314,8 +315,9 @@ func (s *storageImageSource) LayerInfosForCopy(ctx context.Context, instanceDige
 				return nil, fmt.Errorf("TOC digest %q for layer %q is present but %q flag is not set", layer.TOCDigest, layerID, expectedLayerDiffIDFlag)
 			}
 			if expectedDigest, ok := layer.Flags[expectedLayerDiffIDFlag].(string); ok {
-				// if the layer is stored by its TOC, report the expected diffID as the layer Digest
-				// but store the TOC digest so we can later retrieve it from the storage.
+				// If the layer is stored by its TOC, report the expected diffID as the layer Digest;
+				// the generic code is responsible for validating the digest.
+				// We can locate the layer without further c/storage help using s.getBlobMutexProtected.digestToLayerID.
 				blobDigest, err = digest.Parse(expectedDigest)
 				if err != nil {
 					return nil, fmt.Errorf("parsing expected diffID %q for layer %q: %w", expectedDigest, layerID, err)