No longer compute checksum when installing images.

While checksums are verified when a layer is pulled from v2 registries,
there are known issues where the checksum may change when the layer diff
is computed again. To avoid these issues, the checksum should no longer
be computed and stored until after it has been extracted to the docker
storage driver. The checksums are instead computed lazily before they
are pushed to a v2 registry.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

image/image.go

@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"github.com/docker/docker/pkg/archive"
-	"github.com/docker/docker/pkg/tarsum"
 	"github.com/docker/docker/runconfig"
 	"github.com/docker/docker/utils"
 )
@@ -80,48 +79,15 @@ func LoadImage(root string) (*Image, error) {
 
 // StoreImage stores file system layer data for the given image to the
 // image's registered storage driver. Image metadata is stored in a file
-// at the specified root directory. This function also computes a checksum
-// of `layerData` if the image does not have one already.
-func StoreImage(img *Image, layerData archive.ArchiveReader, root string) error {
-	// Store the layer
-	var (
-		size        int64
-		err         error
-		driver      = img.graph.Driver()
-		layerTarSum tarsum.TarSum
-	)
-
-	// If layerData is not nil, unpack it into the new layer
+// at the specified root directory.
+func StoreImage(img *Image, layerData archive.ArchiveReader, root string) (err error) {
+	// Store the layer. If layerData is not nil, unpack it into the new layer
 	if layerData != nil {
-		// If the image doesn't have a checksum, we should add it. The layer
-		// checksums are verified when they are pulled from a remote, but when
-		// a container is committed it should be added here. Also ensure that
-		// the stored checksum has the latest version of tarsum (assuming we
-		// are using tarsum).
-		if tarsum.VersionLabelForChecksum(img.Checksum) != tarsum.Version1.String() {
-			// Either there was no checksum or it's not a tarsum.v1
-			layerDataDecompressed, err := archive.DecompressStream(layerData)
-			if err != nil {
-				return err
-			}
-			defer layerDataDecompressed.Close()
-
-			if layerTarSum, err = tarsum.NewTarSum(layerDataDecompressed, true, tarsum.Version1); err != nil {
-				return err
-			}
-
-			if size, err = driver.ApplyDiff(img.ID, img.Parent, layerTarSum); err != nil {
-				return err
-			}
-
-			img.Checksum = layerTarSum.Sum(nil)
-		} else if size, err = driver.ApplyDiff(img.ID, img.Parent, layerData); err != nil {
+		if img.Size, err = img.graph.Driver().ApplyDiff(img.ID, img.Parent, layerData); err != nil {
 			return err
 		}
-
 	}
 
-	img.Size = size
 	if err := img.SaveSize(root); err != nil {
 		return err
 	}