graph: exported images times matching creation

the image export, that is used in `docker save` previous has just had
the layers times (atimes, mtimes) be when the save was done.
```bash
vbatts@valse ~ (master) $ docker save busybox | tar tv
drwxr-xr-x 0/0               0 2015-09-03 22:22 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/
-rw-r--r-- 0/0               3 2015-09-03 22:22 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/VERSION
-rw-r--r-- 0/0            1405 2015-09-03 22:22 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/json
-rw-r--r-- 0/0         2643968 2015-09-03 22:22 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/layer.tar
drwxr-xr-x 0/0               0 2015-09-03 22:22 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/
-rw-r--r-- 0/0               3 2015-09-03 22:22 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/VERSION
-rw-r--r-- 0/0            1346 2015-09-03 22:22 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/json
-rw-r--r-- 0/0            1024 2015-09-03 22:22 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/layer.tar
drwxr-xr-x 0/0               0 2015-09-03 22:22 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/
-rw-r--r-- 0/0               3 2015-09-03 22:22 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/VERSION
-rw-r--r-- 0/0            1181 2015-09-03 22:22 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/json
-rw-r--r-- 0/0            1024 2015-09-03 22:22 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/layer.tar
-rw-r--r-- 0/0              90 2015-09-03 22:22 repositories
```

With this change, the layer's directory and artifact will have times
matching the image layer's created time. The "repositories" file is set
to epoch.
```bash
vbatts@valse ~ (master) $ docker save busybox | tar tv
drwxr-xr-x 0/0               0 2015-04-17 18:01 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/
-rw-r--r-- 0/0               3 2015-04-17 18:01 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/VERSION
-rw-r--r-- 0/0            1405 2015-04-17 18:01 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/json
-rw-r--r-- 0/0         2643968 2015-04-17 18:01 6ce2e90b0bc7224de3db1f0d646fe8e2c4dd37f1793928287f6074bc451a57ea/layer.tar
drwxr-xr-x 0/0               0 2015-04-17 18:01 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/
-rw-r--r-- 0/0               3 2015-04-17 18:01 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/VERSION
-rw-r--r-- 0/0            1346 2015-04-17 18:01 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/json
-rw-r--r-- 0/0            1024 2015-04-17 18:01 8c2e06607696bd4afb3d03b687e361cc43cf8ec1a4a725bc96e39f05ba97dd55/layer.tar
drwxr-xr-x 0/0               0 2015-04-17 18:01 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/
-rw-r--r-- 0/0               3 2015-04-17 18:01 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/VERSION
-rw-r--r-- 0/0            1181 2015-04-17 18:01 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/json
-rw-r--r-- 0/0            1024 2015-04-17 18:01 cf2616975b4a3cba083ca99bc3f0bf25f5f528c3c52be1596b30f60b0b1c37ff/layer.tar
-rw-r--r-- 0/0              90 1969-12-31 19:00 repositories
```

Side effect of this is that the tar stream from `docker save` is now
more deterministic.
```bash
vbatts@valse ~ (master) $ docker save busybox | sha1sum
baf03e30ef79ca4d9c5e512d3a1b873880f404ca  -
vbatts@valse ~ (master) $ docker save busybox | sha1sum
baf03e30ef79ca4d9c5e512d3a1b873880f404ca  -
vbatts@valse ~ (master) $ docker save busybox | sha1sum
baf03e30ef79ca4d9c5e512d3a1b873880f404ca  -
vbatts@valse ~ (master) $ docker save busybox | sha1sum
baf03e30ef79ca4d9c5e512d3a1b873880f404ca  -
```

Signed-off-by: Vincent Batts <vbatts@redhat.com>

graph/export.go

@@ -2,10 +2,12 @@ package graph
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/pkg/archive"
@@ -88,6 +90,9 @@ func (s *TagStore) ImageExport(names []string, outStream io.Writer) error {
 		if err := f.Close(); err != nil {
 			return err
 		}
+		if err := os.Chtimes(filepath.Join(tempdir, "repositories"), time.Unix(0, 0), time.Unix(0, 0)); err != nil {
+			return err
+		}
 	} else {
 		logrus.Debugf("There were no repositories to write")
 	}
@@ -128,7 +133,11 @@ func (s *TagStore) exportImage(name, tempdir string) error {
 		if err != nil {
 			return err
 		}
-		imageInspectRaw, err := s.lookupRaw(n)
+		img, err := s.LookupImage(n)
+		if err != nil || img == nil {
+			return fmt.Errorf("No such image %s", n)
+		}
+		imageInspectRaw, err := s.graph.RawJSON(img.ID)
 		if err != nil {
 			return err
 		}
@@ -149,11 +158,13 @@ func (s *TagStore) exportImage(name, tempdir string) error {
 			return err
 		}
 
-		// find parent
-		img, err := s.LookupImage(n)
-		if err != nil {
-			return err
+		for _, fname := range []string{"", "VERSION", "json", "layer.tar"} {
+			if err := os.Chtimes(filepath.Join(tmpImageDir, fname), img.Created, img.Created); err != nil {
+				return err
+			}
 		}
+
+		// try again with parent
 		n = img.Parent
 	}
 	return nil

graph/service.go

@@ -10,22 +10,6 @@ import (
 	"github.com/docker/docker/api/types"
 )
 
-// lookupRaw looks up an image by name in a TagStore and returns the raw JSON
-// describing the image.
-func (s *TagStore) lookupRaw(name string) ([]byte, error) {
-	image, err := s.LookupImage(name)
-	if err != nil || image == nil {
-		return nil, fmt.Errorf("No such image %s", name)
-	}
-
-	imageInspectRaw, err := s.graph.RawJSON(image.ID)
-	if err != nil {
-		return nil, err
-	}
-
-	return imageInspectRaw, nil
-}
-
 // Lookup looks up an image by name in a TagStore and returns it as an
 // ImageInspect structure.
 func (s *TagStore) Lookup(name string) (*types.ImageInspect, error) {