Pass PutBlobOptions and TryReusingOptions by address in storage

... to avoid copies.

Keep the interfaces in terms of struct values, to make the
value semantics explicit (and maybe to help the compiler a bit
to show that the data doesn't need to be on a heap).

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

storage/storage_image.go

@@ -459,7 +459,7 @@ func (s *storageImageDestination) HasThreadSafePutBlob() bool {
 // to any other readers for download using the supplied digest.
 // If stream.Read() at any time, ESPECIALLY at end of input, returns an error, PutBlob MUST 1) fail, and 2) delete any data stored so far.
 func (s *storageImageDestination) PutBlobWithOptions(ctx context.Context, stream io.Reader, blobinfo types.BlobInfo, options private.PutBlobOptions) (types.BlobInfo, error) {
-	info, err := s.putBlobToPendingFile(ctx, stream, blobinfo, options)
+	info, err := s.putBlobToPendingFile(ctx, stream, blobinfo, &options)
 	if err != nil {
 		return info, err
 	}
@@ -488,7 +488,7 @@ func (s *storageImageDestination) PutBlob(ctx context.Context, stream io.Reader,
 
 // putBlobToPendingFile implements ImageDestination.PutBlobWithOptions, storing stream into an on-disk file.
 // The caller must arrange the blob to be eventually commited using s.commitLayer().
-func (s *storageImageDestination) putBlobToPendingFile(ctx context.Context, stream io.Reader, blobinfo types.BlobInfo, options private.PutBlobOptions) (types.BlobInfo, error) {
+func (s *storageImageDestination) putBlobToPendingFile(ctx context.Context, stream io.Reader, blobinfo types.BlobInfo, options *private.PutBlobOptions) (types.BlobInfo, error) {
 	// Stores a layer or data blob in our temporary directory, checking that any information
 	// in the blobinfo matches the incoming data.
 	errorBlobInfo := types.BlobInfo{
@@ -617,7 +617,7 @@ func (s *storageImageDestination) PutBlobPartial(ctx context.Context, chunkAcces
 // reflected in the manifest that will be written.
 // If the transport can not reuse the requested blob, TryReusingBlob returns (false, {}, nil); it returns a non-nil error only on an unexpected failure.
 func (s *storageImageDestination) TryReusingBlobWithOptions(ctx context.Context, blobinfo types.BlobInfo, options private.TryReusingBlobOptions) (bool, types.BlobInfo, error) {
-	reused, info, err := s.tryReusingBlobAsPending(ctx, blobinfo, options)
+	reused, info, err := s.tryReusingBlobAsPending(ctx, blobinfo, &options)
 	if err != nil || !reused || options.LayerIndex == nil {
 		return reused, info, err
 	}
@@ -643,7 +643,7 @@ func (s *storageImageDestination) TryReusingBlob(ctx context.Context, blobinfo t
 
 // tryReusingBlobAsPending implements TryReusingBlobWithOptions, filling s.blobDiffIDs and other metadata.
 // The caller must arrange the blob to be eventually commited using s.commitLayer().
-func (s *storageImageDestination) tryReusingBlobAsPending(ctx context.Context, blobinfo types.BlobInfo, options private.TryReusingBlobOptions) (bool, types.BlobInfo, error) {
+func (s *storageImageDestination) tryReusingBlobAsPending(ctx context.Context, blobinfo types.BlobInfo, options *private.TryReusingBlobOptions) (bool, types.BlobInfo, error) {
 	// lock the entire method as it executes fairly quickly
 	s.lock.Lock()
 	defer s.lock.Unlock()