From 49c3a7c4bac2877265ef8c4eaf210159560f08b4 Mon Sep 17 00:00:00 2001
From: Lei Jitang <leijitang@huawei.com>
Date: Tue, 1 Aug 2017 08:05:27 -0400
Subject: [PATCH] Fallback to use naive diff driver if enable
 CONFIG_OVERLAY_FS_REDIRECT_DIR

When use overlay2 as the graphdriver and the kernel enable
`CONFIG_OVERLAY_FS_REDIRECT_DIR=y`, rename a dir in lower layer
will has a xattr to redirct its dir to source dir. This make the
image layer unportable. This patch fallback to use naive diff driver
when kernel enable CONFIG_OVERLAY_FS_REDIRECT_DIR

Signed-off-by: Lei Jitang <leijitang@huawei.com>
---
 daemon/graphdriver/overlay2/check.go   | 31 ++++++++++++++++++++++----
 daemon/graphdriver/overlay2/overlay.go |  4 ++--
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/daemon/graphdriver/overlay2/check.go b/daemon/graphdriver/overlay2/check.go
index 35e088aa32..fac147f363 100644
--- a/daemon/graphdriver/overlay2/check.go
+++ b/daemon/graphdriver/overlay2/check.go
@@ -8,6 +8,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"syscall"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/pkg/system"
@@ -15,10 +16,11 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-// hasOpaqueCopyUpBug checks whether the filesystem has a bug
+// doesSupportNativeDiff checks whether the filesystem has a bug
 // which copies up the opaque flag when copying up an opaque
-// directory. When this bug exists naive diff should be used.
-func hasOpaqueCopyUpBug(d string) error {
+// directory or the kernel enable CONFIG_OVERLAY_FS_REDIRECT_DIR.
+// When these exist naive diff should be used.
+func doesSupportNativeDiff(d string) error {
 	td, err := ioutil.TempDir(d, "opaque-bug-check")
 	if err != nil {
 		return err
@@ -29,10 +31,13 @@ func hasOpaqueCopyUpBug(d string) error {
 		}
 	}()
 
-	// Make directories l1/d, l2/d, l3, work, merged
+	// Make directories l1/d, l1/d1, l2/d, l3, work, merged
 	if err := os.MkdirAll(filepath.Join(td, "l1", "d"), 0755); err != nil {
 		return err
 	}
+	if err := os.MkdirAll(filepath.Join(td, "l1", "d1"), 0755); err != nil {
+		return err
+	}
 	if err := os.MkdirAll(filepath.Join(td, "l2", "d"), 0755); err != nil {
 		return err
 	}
@@ -75,5 +80,23 @@ func hasOpaqueCopyUpBug(d string) error {
 		return errors.New("opaque flag erroneously copied up, consider update to kernel 4.8 or later to fix")
 	}
 
+	// rename "d1" to "d2"
+	if err := os.Rename(filepath.Join(td, "merged", "d1"), filepath.Join(td, "merged", "d2")); err != nil {
+		// if rename failed with syscall.EXDEV, the kernel doesn't have CONFIG_OVERLAY_FS_REDIRECT_DIR enabled
+		if err.(*os.LinkError).Err == syscall.EXDEV {
+			return nil
+		}
+		return errors.Wrap(err, "failed to rename dir in merged directory")
+	}
+	// get the xattr of "d2"
+	xattrRedirect, err := system.Lgetxattr(filepath.Join(td, "l3", "d2"), "trusted.overlay.redirect")
+	if err != nil {
+		return errors.Wrap(err, "failed to read redirect flag on upper layer")
+	}
+
+	if string(xattrRedirect) == "d1" {
+		return errors.New("kernel has CONFIG_OVERLAY_FS_REDIRECT_DIR enabled")
+	}
+
 	return nil
 }
diff --git a/daemon/graphdriver/overlay2/overlay.go b/daemon/graphdriver/overlay2/overlay.go
index 4ef2a8caaf..6a417e8213 100644
--- a/daemon/graphdriver/overlay2/overlay.go
+++ b/daemon/graphdriver/overlay2/overlay.go
@@ -266,8 +266,8 @@ func supportsOverlay() error {
 
 func useNaiveDiff(home string) bool {
 	useNaiveDiffLock.Do(func() {
-		if err := hasOpaqueCopyUpBug(home); err != nil {
-			logrus.Warnf("Not using native diff for overlay2: %v", err)
+		if err := doesSupportNativeDiff(home); err != nil {
+			logrus.Warnf("Not using native diff for overlay2, this may cause degraded performance for building images: %v", err)
 			useNaiveDiffOnly = true
 		}
 	})