From 242fd4b3ef32b5a20135d6031040bcf099b5df4e Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Tue, 19 Nov 2013 13:09:36 +0100
Subject: [PATCH] dummy driver: Use cp --reflink=auto to copy directories

On systems that supports reflinking (i.e. btrfs) this means the dummy
backend is much faster at copying files and will be sharing file data in
a CoW fashion.

On my (btrfs) system this makes "docker run ubuntu echo hello world" go
from about 3 seconds to about 1 second. Not instant, but clearly better.

cp --reflink=auto is availible since coreutils 7.5 (around 2009), so this
seems pretty ok to rely on.

cp is also better at preserving file metadata than tar, so for instance
it will copy xattrs.
---
 graphdriver/dummy/driver.go | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/graphdriver/dummy/driver.go b/graphdriver/dummy/driver.go
index 4ca8fac58a..ec324a88b5 100644
--- a/graphdriver/dummy/driver.go
+++ b/graphdriver/dummy/driver.go
@@ -2,9 +2,9 @@ package dummy
 
 import (
 	"fmt"
-	"github.com/dotcloud/docker/archive"
 	"github.com/dotcloud/docker/graphdriver"
 	"os"
+	"os/exec"
 	"path"
 )
 
@@ -35,6 +35,14 @@ func (d *Driver) Cleanup() error {
 	return nil
 }
 
+func copyDir(src, dst string) error {
+	cmd := exec.Command("cp", "-aT", "--reflink=auto", src, dst)
+	if err := cmd.Run(); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (d *Driver) Create(id string, parent string) error {
 	dir := d.dir(id)
 	if err := os.MkdirAll(path.Dir(dir), 0700); err != nil {
@@ -50,7 +58,7 @@ func (d *Driver) Create(id string, parent string) error {
 	if err != nil {
 		return fmt.Errorf("%s: %s", parent, err)
 	}
-	if err := archive.CopyWithTar(parentDir, dir); err != nil {
+	if err := copyDir(parentDir, dir); err != nil {
 		return err
 	}
 	return nil