Export storage.CreateOptions in top-level package

Let the options for `BlobStore.Create()` be modified in middleware
wrappers.

Signed-off-by: Michal Minar <miminar@redhat.com>

registry/storage/linkedblobstore_test.go

@@ -0,0 +1,78 @@
+package storage
+
+import (
+	"io"
+	"testing"
+
+	"github.com/docker/distribution"
+	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/digest"
+
+	"github.com/docker/distribution/reference"
+	"github.com/docker/distribution/testutil"
+)
+
+func TestLinkedBlobStoreCreateWithMountFrom(t *testing.T) {
+	fooRepoName, _ := reference.ParseNamed("nm/foo")
+	fooEnv := newManifestStoreTestEnv(t, fooRepoName, "thetag")
+	ctx := context.Background()
+
+	// Build up some test layers and add them to the manifest, saving the
+	// readseekers for upload later.
+	testLayers := map[digest.Digest]io.ReadSeeker{}
+	for i := 0; i < 2; i++ {
+		rs, ds, err := testutil.CreateRandomTarFile()
+		if err != nil {
+			t.Fatalf("unexpected error generating test layer file")
+		}
+		dgst := digest.Digest(ds)
+
+		testLayers[digest.Digest(dgst)] = rs
+	}
+
+	// upload the layers to foo/bar
+	for dgst, rs := range testLayers {
+		wr, err := fooEnv.repository.Blobs(fooEnv.ctx).Create(fooEnv.ctx)
+		if err != nil {
+			t.Fatalf("unexpected error creating test upload: %v", err)
+		}
+
+		if _, err := io.Copy(wr, rs); err != nil {
+			t.Fatalf("unexpected error copying to upload: %v", err)
+		}
+
+		if _, err := wr.Commit(fooEnv.ctx, distribution.Descriptor{Digest: dgst}); err != nil {
+			t.Fatalf("unexpected error finishing upload: %v", err)
+		}
+	}
+
+	// create another repository nm/bar
+	barRepoName, _ := reference.ParseNamed("nm/bar")
+
+	barRepo, err := fooEnv.registry.Repository(ctx, barRepoName)
+	if err != nil {
+		t.Fatalf("unexpected error getting repo: %v", err)
+	}
+
+	// cross-repo mount the test layers into a nm/bar
+	for dgst := range testLayers {
+		fooCanonical, _ := reference.WithDigest(fooRepoName, dgst)
+		option := WithMountFrom(fooCanonical)
+		// ensure we can instrospect it
+		createOpts := distribution.CreateOptions{}
+		if err := option.Apply(&createOpts); err != nil {
+			t.Fatalf("failed to apply MountFrom option: %v", err)
+		}
+		if !createOpts.Mount.ShouldMount || createOpts.Mount.From.String() != fooCanonical.String() {
+			t.Fatalf("unexpected create options: %#+v", createOpts.Mount)
+		}
+
+		_, err := barRepo.Blobs(ctx).Create(ctx, WithMountFrom(fooCanonical))
+		if err == nil {
+			t.Fatalf("unexpected non-error while mounting from %q: %v", fooRepoName.String(), err)
+		}
+		if _, ok := err.(distribution.ErrBlobMounted); !ok {
+			t.Fatalf("expected ErrMountFrom error, not %T: %v", err, err)
+		}
+	}
+}