Merge pull request #815 from AkihiroSuda/dtype

overlay: abort if backing fs lacks support for d_type

fs/fsutils/fsutils_linux.go

@@ -0,0 +1,87 @@
+// +build linux
+
+package fsutils
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func locateDummyIfEmpty(path string) (string, error) {
+	children, err := ioutil.ReadDir(path)
+	if err != nil {
+		return "", err
+	}
+	if len(children) != 0 {
+		return "", nil
+	}
+	dummyFile, err := ioutil.TempFile(path, "fsutils-dummy")
+	if err != nil {
+		return "", err
+	}
+	name := dummyFile.Name()
+	err = dummyFile.Close()
+	return name, err
+}
+
+// SupportsDType returns whether the filesystem mounted on path supports d_type
+func SupportsDType(path string) (bool, error) {
+	// locate dummy so that we have at least one dirent
+	dummy, err := locateDummyIfEmpty(path)
+	if err != nil {
+		return false, err
+	}
+	if dummy != "" {
+		defer os.Remove(dummy)
+	}
+
+	visited := 0
+	supportsDType := true
+	fn := func(ent *syscall.Dirent) bool {
+		visited++
+		if ent.Type == syscall.DT_UNKNOWN {
+			supportsDType = false
+			// stop iteration
+			return true
+		}
+		// continue iteration
+		return false
+	}
+	if err = iterateReadDir(path, fn); err != nil {
+		return false, err
+	}
+	if visited == 0 {
+		return false, fmt.Errorf("did not hit any dirent during iteration %s", path)
+	}
+	return supportsDType, nil
+}
+
+func iterateReadDir(path string, fn func(*syscall.Dirent) bool) error {
+	d, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer d.Close()
+	fd := int(d.Fd())
+	buf := make([]byte, 4096)
+	for {
+		nbytes, err := syscall.ReadDirent(fd, buf)
+		if err != nil {
+			return err
+		}
+		if nbytes == 0 {
+			break
+		}
+		for off := 0; off < nbytes; {
+			ent := (*syscall.Dirent)(unsafe.Pointer(&buf[off]))
+			if stop := fn(ent); stop {
+				return nil
+			}
+			off += int(ent.Reclen)
+		}
+	}
+	return nil
+}

fs/fsutils/fsutils_linux_test.go

@@ -0,0 +1,91 @@
+// +build linux
+
+package fsutils
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"syscall"
+	"testing"
+)
+
+func testSupportsDType(t *testing.T, expected bool, mkfsCommand string, mkfsArg ...string) {
+	// check whether mkfs is installed
+	if _, err := exec.LookPath(mkfsCommand); err != nil {
+		t.Skipf("%s not installed: %v", mkfsCommand, err)
+	}
+
+	// create a sparse image
+	imageSize := int64(32 * 1024 * 1024)
+	imageFile, err := ioutil.TempFile("", "fsutils-image")
+	if err != nil {
+		t.Fatal(err)
+	}
+	imageFileName := imageFile.Name()
+	defer os.Remove(imageFileName)
+	if _, err = imageFile.Seek(imageSize-1, 0); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = imageFile.Write([]byte{0}); err != nil {
+		t.Fatal(err)
+	}
+	if err = imageFile.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	// create a mountpoint
+	mountpoint, err := ioutil.TempDir("", "fsutils-mountpoint")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(mountpoint)
+
+	// format the image
+	args := append(mkfsArg, imageFileName)
+	t.Logf("Executing `%s %v`", mkfsCommand, args)
+	out, err := exec.Command(mkfsCommand, args...).CombinedOutput()
+	if len(out) > 0 {
+		t.Log(string(out))
+	}
+	if err != nil {
+		t.Skip("skipping the test because %s failed. This is probably your %s is an unsupported version.", mkfsCommand, mkfsCommand)
+	}
+
+	// loopback-mount the image.
+	// for ease of setting up loopback device, we use os/exec rather than syscall.Mount
+	out, err = exec.Command("mount", "-o", "loop", imageFileName, mountpoint).CombinedOutput()
+	if len(out) > 0 {
+		t.Log(string(out))
+	}
+	if err != nil {
+		t.Skip("skipping the test because mount failed")
+	}
+	defer func() {
+		if err := syscall.Unmount(mountpoint, 0); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	// check whether it supports d_type
+	result, err := SupportsDType(mountpoint)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Supports d_type: %v", result)
+	if result != expected {
+		t.Fatalf("expected %v, got %v", expected, result)
+	}
+}
+
+func TestSupportsDTypeWithFType0XFS(t *testing.T) {
+	testSupportsDType(t, false, "mkfs.xfs", "-m", "crc=0", "-n", "ftype=0")
+}
+
+func TestSupportsDTypeWithFType1XFS(t *testing.T) {
+	testSupportsDType(t, true, "mkfs.xfs", "-m", "crc=0", "-n", "ftype=1")
+}
+
+func TestSupportsDTypeWithExt4(t *testing.T) {
+	testSupportsDType(t, true, "mkfs.ext4", "-F")
+}

snapshot/overlay/overlay.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/fs"
+	"github.com/containerd/containerd/fs/fsutils"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshot"
@@ -47,6 +48,13 @@ func NewSnapshotter(root string) (snapshot.Snapshotter, error) {
 	if err := os.MkdirAll(root, 0700); err != nil {
 		return nil, err
 	}
+	supportsDType, err := fsutils.SupportsDType(root)
+	if err != nil {
+		return nil, err
+	}
+	if !supportsDType {
+		return nil, fmt.Errorf("%s does not support d_type. If the backing filesystem is xfs, please reformat with ftype=1 to enable d_type support.", root)
+	}
 	ms, err := storage.NewMetaStore(filepath.Join(root, "metadata.db"))
 	if err != nil {
 		return nil, err