This fixes a bug in the interaction between volumes in base images (#555)

and our snapshot optimizations.

If a previous base image has a volume, the directory is added to the
list of files to snapshot. That directory may not actually exist in the image.

integration/dockerfiles/Dockerfile_test_volume_4

@@ -0,0 +1,5 @@
+FROM rabbitmq@sha256:57b028a4bb9592ece3915e3e9cdbbaecb3eb82b753aaaf5250f8d25d81d318e2
+# This base image has a volume declared at /var/lib/rabbitmq
+# This is important because it should not exist in the child image.
+COPY context/foo /usr/local/bin/
+CMD ["script.sh"]

pkg/commands/volume.go

@@ -48,10 +48,7 @@ func (v *VolumeCommand) ExecuteCommand(config *v1.Config, buildArgs *dockerfile.
 	for _, volume := range resolvedVolumes {
 		var x struct{}
 		existingVolumes[volume] = x
-		err := util.AddVolumePathToWhitelist(volume)
-		if err != nil {
-			return err
-		}
+		util.AddVolumePathToWhitelist(volume)
 
 		// Only create and snapshot the dir if it didn't exist already
 		if _, err := os.Stat(volume); os.IsNotExist(err) {

pkg/executor/build.go

@@ -285,11 +285,8 @@ func (s *stageBuilder) takeSnapshot(files []string) (string, error) {
 	if files == nil || s.opts.SingleSnapshot {
 		snapshot, err = s.snapshotter.TakeSnapshotFS()
 	} else {
-		// Volumes are very weird. They get created in their command, but snapshotted in the next one.
-		// Add them to the list of files to snapshot.
-		for v := range s.cf.Config.Volumes {
-			files = append(files, v)
-		}
+		// Volumes are very weird. They get snapshotted in the next command.
+		files = append(files, util.Volumes()...)
 		snapshot, err = s.snapshotter.TakeSnapshot(files)
 	}
 	timing.DefaultRun.Stop(t)

pkg/util/fs_util.go

@@ -64,6 +64,8 @@ var initialWhitelist = []WhitelistEntry{
 
 var whitelist = initialWhitelist
 
+var volumes = []string{}
+
 var excluded []string
 
 // GetFSFromImage extracts the layers of img to root
@@ -308,6 +310,7 @@ func CheckWhitelist(path string) (bool, error) {
 			return true, nil
 		}
 	}
+
 	return false, nil
 }
 
@@ -331,6 +334,7 @@ func checkWhitelistRoot(root string) bool {
 // From: https://www.kernel.org/doc/Documentation/filesystems/proc.txt
 func DetectFilesystemWhitelist(path string) error {
 	whitelist = initialWhitelist
+	volumes = []string{}
 	f, err := os.Open(path)
 	if err != nil {
 		return err
@@ -443,16 +447,14 @@ func CreateFile(path string, reader io.Reader, perm os.FileMode, uid uint32, gid
 	return dest.Chown(int(uid), int(gid))
 }
 
-// AddVolumePathToWhitelist adds the given path to the whitelist with
-// PrefixMatchOnly set to true. Snapshotting will ignore paths prefixed
-// with the volume, but the volume itself will not be ignored.
-func AddVolumePathToWhitelist(path string) error {
+// AddVolumePath adds the given path to the volume whitelist.
+func AddVolumePathToWhitelist(path string) {
 	logrus.Infof("adding volume %s to whitelist", path)
 	whitelist = append(whitelist, WhitelistEntry{
 		Path:            path,
 		PrefixMatchOnly: true,
 	})
-	return nil
+	volumes = append(volumes, path)
 }
 
 // DownloadFileToDest downloads the file at rawurl to the given dest for the ADD command
@@ -620,3 +622,7 @@ func HasFilepathPrefix(path, prefix string, prefixMatchOnly bool) bool {
 	}
 	return true
 }
+
+func Volumes() []string {
+	return volumes
+}