bugfix: updatedAt timestamp file may be empty

Signed-off-by: Michael Wan <zirenwan@gmail.com>

content/local/store.go

@@ -33,6 +33,8 @@ import (
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/filters"
 	"github.com/containerd/containerd/log"
+
+	"github.com/containerd/continuity"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
@@ -651,5 +653,5 @@ func writeTimestampFile(p string, t time.Time) error {
 		return err
 	}
 
-	return ioutil.WriteFile(p, b, 0666)
+	return continuity.AtomicWriteFile(p, b, 0666)
 }