Have VFS graphdriver use accelerated in-kernel copy

This change makes the VFS graphdriver use the kernel-accelerated
(copy_file_range) mechanism of copying files, which is able to
leverage reflinks.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>

daemon/graphdriver/copy/copy.go

@@ -113,7 +113,9 @@ type fileID struct {
 
 // DirCopy copies or hardlinks the contents of one directory to another,
 // properly handling xattrs, and soft links
-func DirCopy(srcDir, dstDir string, copyMode Mode) error {
+//
+// Copying xattrs can be opted out of by passing false for copyXattrs.
+func DirCopy(srcDir, dstDir string, copyMode Mode, copyXattrs bool) error {
 	copyWithFileRange := true
 	copyWithFileClone := true
 	// This is a map of source file inodes to dst file paths
@@ -206,16 +208,10 @@ func DirCopy(srcDir, dstDir string, copyMode Mode) error {
 			return err
 		}
 
-		if err := copyXattr(srcPath, dstPath, "security.capability"); err != nil {
+		if copyXattrs {
+			if err := doCopyXattrs(srcPath, dstPath); err != nil {
 				return err
 			}
-
-		// We need to copy this attribute if it appears in an overlay upper layer, as
-		// this function is used to copy those. It is set by overlay if a directory
-		// is removed and then re-created and should not inherit anything from the
-		// same dir in the lower dir.
-		if err := copyXattr(srcPath, dstPath, "trusted.overlay.opaque"); err != nil {
-			return err
 		}
 
 		isSymlink := f.Mode()&os.ModeSymlink != 0
@@ -246,3 +242,18 @@ func DirCopy(srcDir, dstDir string, copyMode Mode) error {
 	})
 	return err
 }
+
+func doCopyXattrs(srcPath, dstPath string) error {
+	if err := copyXattr(srcPath, dstPath, "security.capability"); err != nil {
+		return err
+	}
+
+	// We need to copy this attribute if it appears in an overlay upper layer, as
+	// this function is used to copy those. It is set by overlay if a directory
+	// is removed and then re-created and should not inherit anything from the
+	// same dir in the lower dir.
+	if err := copyXattr(srcPath, dstPath, "trusted.overlay.opaque"); err != nil {
+		return err
+	}
+	return nil
+}

daemon/graphdriver/copy/copy_test.go

@@ -86,7 +86,7 @@ func TestCopyHardlink(t *testing.T) {
 	require.NoError(t, ioutil.WriteFile(srcFile1, []byte{}, 0777))
 	require.NoError(t, os.Link(srcFile1, srcFile2))
 
-	assert.NoError(t, DirCopy(srcDir, dstDir, Content))
+	assert.NoError(t, DirCopy(srcDir, dstDir, Content, false))
 
 	require.NoError(t, unix.Stat(srcFile1, &srcFile1FileInfo))
 	require.NoError(t, unix.Stat(srcFile2, &srcFile2FileInfo))

daemon/graphdriver/overlay/overlay.go

@@ -330,7 +330,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 
-	return copy.DirCopy(parentUpperDir, upperDir, copy.Content)
+	return copy.DirCopy(parentUpperDir, upperDir, copy.Content, true)
 }
 
 func (d *Driver) dir(id string) string {
@@ -446,7 +446,7 @@ func (d *Driver) ApplyDiff(id string, parent string, diff io.Reader) (size int64
 		}
 	}()
 
-	if err = copy.DirCopy(parentRootDir, tmpRootDir, copy.Hardlink); err != nil {
+	if err = copy.DirCopy(parentRootDir, tmpRootDir, copy.Hardlink, true); err != nil {
 		return 0, err
 	}
 

daemon/graphdriver/vfs/copy_linux.go

@@ -0,0 +1,9 @@
+// +build linux
+
+package vfs
+
+import "github.com/docker/docker/daemon/graphdriver/copy"
+
+func dirCopy(srcDir, dstDir string) error {
+	return copy.DirCopy(srcDir, dstDir, copy.Content, false)
+}

daemon/graphdriver/vfs/copy_unsupported.go

@@ -0,0 +1,9 @@
+// +build !linux
+
+package vfs
+
+import "github.com/docker/docker/pkg/chrootarchive"
+
+func dirCopy(srcDir, dstDir string) error {
+	return chrootarchive.NewArchiver(nil).CopyWithTar(srcDir, dstDir)
+}

daemon/graphdriver/vfs/driver.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/docker/docker/daemon/graphdriver/quota"
-	"github.com/docker/docker/pkg/chrootarchive"
 	"github.com/docker/docker/pkg/containerfs"
 	"github.com/docker/docker/pkg/idtools"
 	"github.com/docker/docker/pkg/system"
@@ -16,8 +15,8 @@ import (
 )
 
 var (
-	// CopyWithTar defines the copy method to use.
+	// CopyDir defines the copy method to use.
-	CopyWithTar = chrootarchive.NewArchiver(nil).CopyWithTar
+	CopyDir = dirCopy
 )
 
 func init() {
@@ -133,7 +132,7 @@ func (d *Driver) create(id, parent string, size uint64) error {
 	if err != nil {
 		return fmt.Errorf("%s: %s", parent, err)
 	}
-	return CopyWithTar(parentDir.Path(), dir)
+	return CopyDir(parentDir.Path(), dir)
 }
 
 func (d *Driver) dir(id string) string {

layer/layer_test.go

@@ -23,7 +23,7 @@ import (
 func init() {
 	graphdriver.ApplyUncompressedLayer = archive.UnpackLayer
 	defaultArchiver := archive.NewDefaultArchiver()
-	vfs.CopyWithTar = defaultArchiver.CopyWithTar
+	vfs.CopyDir = defaultArchiver.CopyWithTar
 }
 
 func newVFSGraphDriver(td string) (graphdriver.Driver, error) {