@@ -10,6 +10,7 @@ import (

 	"github.com/Sirupsen/logrus"

 	"github.com/docker/docker/pkg/ioutils"

 	"github.com/opencontainers/go-digest"

+	"github.com/pkg/errors"

 )

 // DigestWalkFunc is function called by StoreBackend.Walk

@@ -47,10 +48,10 @@ func newFSStore(root string) (*fs, error) {

 		root: root,

 	}

 	if err := os.MkdirAll(filepath.Join(root, contentDirName, string(digest.Canonical)), 0700); err != nil {

-		return nil, err

+		return nil, errors.Wrap(err, "failed to create storage backend")

 	}

 	if err := os.MkdirAll(filepath.Join(root, metadataDirName, string(digest.Canonical)), 0700); err != nil {

-		return nil, err

+		return nil, errors.Wrap(err, "failed to create storage backend")

 	}

 	return s, nil

 }

@@ -96,7 +97,7 @@ func (s *fs) Get(dgst digest.Digest) ([]byte, error) {

 func (s *fs) get(dgst digest.Digest) ([]byte, error) {

 	content, err := ioutil.ReadFile(s.contentFile(dgst))

 	if err != nil {

-		return nil, err

+		return nil, errors.Wrapf(err, "failed to get digest %s", dgst)

 	}

 	// todo: maybe optional

@@ -118,7 +119,7 @@ func (s *fs) Set(data []byte) (digest.Digest, error) {

 	dgst := digest.FromBytes(data)

 	if err := ioutils.AtomicWriteFile(s.contentFile(dgst), data, 0600); err != nil {

-		return "", err

+		return "", errors.Wrap(err, "failed to write digest data")

 	}

 	return dgst, nil

@@ -161,7 +162,11 @@ func (s *fs) GetMetadata(dgst digest.Digest, key string) ([]byte, error) {

 	if _, err := s.get(dgst); err != nil {

 		return nil, err

 	}

-	return ioutil.ReadFile(filepath.Join(s.metadataDir(dgst), key))

+	bytes, err := ioutil.ReadFile(filepath.Join(s.metadataDir(dgst), key))

+	if err != nil {

+		return nil, errors.Wrap(err, "failed to read metadata")

+	}

+	return bytes, nil

 }

 // DeleteMetadata removes the metadata associated with a digest.

@@ -50,7 +50,7 @@ func TestFSInvalidSet(t *testing.T) {

 	assert.NilError(t, err)

 	_, err = store.Set([]byte("foobar"))

-	assert.Error(t, err, "is a directory")

+	assert.Error(t, err, "failed to write digest data")

 }

 func TestFSInvalidRoot(t *testing.T) {

@@ -73,11 +73,11 @@ func TestFSInvalidRoot(t *testing.T) {

 		assert.NilError(t, err)

 		f, err := os.Create(filePath)

-		defer f.Close()

 		assert.NilError(t, err)

+		f.Close()

 		_, err = NewFSStoreBackend(root)

-		assert.Error(t, err, "not a directory")

+		assert.Error(t, err, "failed to create storage backend")

 		os.RemoveAll(root)

 	}

@@ -117,14 +117,14 @@ func TestFSMetadataGetSet(t *testing.T) {

 	}

 	_, err = store.GetMetadata(id2, "tkey2")

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to read metadata")

 	id3 := digest.FromBytes([]byte("baz"))

 	err = store.SetMetadata(id3, "tkey", []byte("tval"))

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to get digest")

 	_, err = store.GetMetadata(id3, "tkey")

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to get digest")

 }

 func TestFSInvalidWalker(t *testing.T) {

@@ -194,7 +194,7 @@ func TestFSGetUnsetKey(t *testing.T) {

 	for _, key := range []digest.Digest{"foobar:abc", "sha256:abc", "sha256:c3ab8ff13720e8ad9047dd39466b3c8974e592c2fa383d4a3960714caef0c4f2a"} {

 		_, err := store.Get(key)

-		assert.Error(t, err, "no such file or directory")

+		assert.Error(t, err, "failed to get digest")

 	}

 }

@@ -222,7 +222,7 @@ func TestFSDelete(t *testing.T) {

 	assert.NilError(t, err)

 	_, err = store.Get(id)

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to get digest")

 	_, err = store.Get(id2)

 	assert.NilError(t, err)

@@ -231,7 +231,7 @@ func TestFSDelete(t *testing.T) {

 	assert.NilError(t, err)

 	_, err = store.Get(id2)

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to get digest")

 }

 func TestFSWalker(t *testing.T) {

@@ -40,7 +40,7 @@ func TestRestore(t *testing.T) {

 	assert.Equal(t, img2.Comment, "def")

 	p, err := is.GetParent(ID(id1))

-	assert.Error(t, err, "no such file")

+	assert.Error(t, err, "failed to read metadata")

 	p, err = is.GetParent(ID(id2))

 	assert.NilError(t, err)

@@ -90,13 +90,13 @@ func TestAddDelete(t *testing.T) {

 	assert.NilError(t, err)

 	_, err = is.Get(id1)

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to get digest")

 	_, err = is.Get(id2)

 	assert.NilError(t, err)

 	_, err = is.GetParent(id2)

-	assert.Error(t, err, "no such file or directory")

+	assert.Error(t, err, "failed to read metadata")

 }

 func TestSearchAfterDelete(t *testing.T) {