From d0779a6145d5bd8b2245f751d27a7bfaeedc01ca Mon Sep 17 00:00:00 2001
From: Lantao Liu <lantaol@google.com>
Date: Thu, 1 Feb 2018 02:28:26 +0000
Subject: [PATCH] Simplify mount.Lookup.

Signed-off-by: Lantao Liu <lantaol@google.com>
---
 mount/lookup_test/lookup_linux_test.go | 60 +++++++++++++++++++++-----
 mount/lookup_unix.go                   | 19 +++-----
 2 files changed, 54 insertions(+), 25 deletions(-)

diff --git a/mount/lookup_test/lookup_linux_test.go b/mount/lookup_test/lookup_linux_test.go
index 852053369..2c9070428 100644
--- a/mount/lookup_test/lookup_linux_test.go
+++ b/mount/lookup_test/lookup_linux_test.go
@@ -10,6 +10,7 @@
 package lookuptest
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -20,18 +21,19 @@ import (
 	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/testutil"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
-func testLookup(t *testing.T, fsType string) {
-	checkLookup := func(mntPoint, dir string) {
-		info, err := mount.Lookup(dir)
-		if err != nil {
-			t.Fatal(err)
-		}
-		assert.Equal(t, fsType, info.FSType)
-		assert.Equal(t, mntPoint, info.Mountpoint)
+func checkLookup(t *testing.T, fsType, mntPoint, dir string) {
+	info, err := mount.Lookup(dir)
+	if err != nil {
+		t.Fatal(err)
 	}
+	assert.Equal(t, fsType, info.FSType)
+	assert.Equal(t, mntPoint, info.Mountpoint)
+}
 
+func testLookup(t *testing.T, fsType string) {
 	testutil.RequiresRoot(t)
 	mnt, err := ioutil.TempDir("", "containerd-mountinfo-test-lookup")
 	if err != nil {
@@ -56,7 +58,7 @@ func testLookup(t *testing.T, fsType string) {
 		cleanupDevice()
 	}()
 	assert.True(t, strings.HasPrefix(deviceName, "/dev/loop"))
-	checkLookup(mnt, mnt)
+	checkLookup(t, fsType, mnt, mnt)
 
 	newMnt, err := ioutil.TempDir("", "containerd-mountinfo-test-newMnt")
 	if err != nil {
@@ -70,14 +72,14 @@ func testLookup(t *testing.T, fsType string) {
 	defer func() {
 		testutil.Unmount(t, newMnt)
 	}()
-	checkLookup(newMnt, newMnt)
+	checkLookup(t, fsType, newMnt, newMnt)
 
 	subDir := filepath.Join(newMnt, "subDir")
 	err = os.MkdirAll(subDir, 0700)
 	if err != nil {
 		t.Fatal(err)
 	}
-	checkLookup(newMnt, subDir)
+	checkLookup(t, fsType, newMnt, subDir)
 }
 
 func TestLookupWithExt4(t *testing.T) {
@@ -87,3 +89,39 @@ func TestLookupWithExt4(t *testing.T) {
 func TestLookupWithXFS(t *testing.T) {
 	testLookup(t, "xfs")
 }
+
+func TestLookupWithOverlay(t *testing.T) {
+	lower, err := ioutil.TempDir("", "containerd-mountinfo-test-lower")
+	require.NoError(t, err)
+	defer os.RemoveAll(lower)
+
+	upper, err := ioutil.TempDir("", "containerd-mountinfo-test-upper")
+	require.NoError(t, err)
+	defer os.RemoveAll(upper)
+
+	work, err := ioutil.TempDir("", "containerd-mountinfo-test-work")
+	require.NoError(t, err)
+	defer os.RemoveAll(work)
+
+	overlay, err := ioutil.TempDir("", "containerd-mountinfo-test-overlay")
+	require.NoError(t, err)
+	defer os.RemoveAll(overlay)
+
+	if out, err := exec.Command("mount", "-t", "overlay", "overlay", "-o", fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s",
+		lower, upper, work), overlay).CombinedOutput(); err != nil {
+		// not fatal
+		t.Skipf("could not mount overlay: %v (out: %q)", err, string(out))
+	}
+	defer testutil.Unmount(t, overlay)
+
+	testdir := filepath.Join(overlay, "testdir")
+	err = os.Mkdir(testdir, 0777)
+	require.NoError(t, err)
+
+	testfile := filepath.Join(overlay, "testfile")
+	_, err = os.Create(testfile)
+	require.NoError(t, err)
+
+	checkLookup(t, "overlay", overlay, testdir)
+	checkLookup(t, "overlay", overlay, testfile)
+}
diff --git a/mount/lookup_unix.go b/mount/lookup_unix.go
index df9625a96..6e4fd0d24 100644
--- a/mount/lookup_unix.go
+++ b/mount/lookup_unix.go
@@ -3,22 +3,16 @@
 package mount
 
 import (
-	"fmt"
 	"path/filepath"
 	"sort"
 	"strings"
-	"syscall"
 
 	"github.com/pkg/errors"
 )
 
 // Lookup returns the mount info corresponds to the path.
 func Lookup(dir string) (Info, error) {
-	var dirStat syscall.Stat_t
 	dir = filepath.Clean(dir)
-	if err := syscall.Stat(dir, &dirStat); err != nil {
-		return Info{}, errors.Wrapf(err, "failed to access %q", dir)
-	}
 
 	mounts, err := Self()
 	if err != nil {
@@ -26,21 +20,18 @@ func Lookup(dir string) (Info, error) {
 	}
 
 	// Sort descending order by Info.Mountpoint
-	sort.Slice(mounts, func(i, j int) bool {
+	sort.SliceStable(mounts, func(i, j int) bool {
 		return mounts[j].Mountpoint < mounts[i].Mountpoint
 	})
 	for _, m := range mounts {
 		// Note that m.{Major, Minor} are generally unreliable for our purpose here
 		// https://www.spinics.net/lists/linux-btrfs/msg58908.html
-		var st syscall.Stat_t
-		if err := syscall.Stat(m.Mountpoint, &st); err != nil {
-			// may fail; ignore err
-			continue
-		}
-		if st.Dev == dirStat.Dev && strings.HasPrefix(dir, m.Mountpoint) {
+		// Note that device number is not checked here, because for overlayfs files
+		// may have different device number with the mountpoint.
+		if strings.HasPrefix(dir, m.Mountpoint) {
 			return m, nil
 		}
 	}
 
-	return Info{}, fmt.Errorf("failed to find the mount info for %q", dir)
+	return Info{}, errors.Errorf("failed to find the mount info for %q", dir)
 }