Merge pull request #2159 from AkihiroSuda/check-overlay

overlay: add Supported() checker

snapshots/overlay/check.go

@@ -0,0 +1,88 @@
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package overlay
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/mount"
+	"github.com/containerd/continuity/fs"
+	"github.com/pkg/errors"
+)
+
+// supportsMultipleLowerDir checks if the system supports multiple lowerdirs,
+// which is required for the overlay snapshotter. On 4.x kernels, multiple lowerdirs
+// are always available (so this check isn't needed), and backported to RHEL and
+// CentOS 3.x kernels (3.10.0-693.el7.x86_64 and up). This function is to detect
+// support on those kernels, without doing a kernel version compare.
+//
+// Ported from moby overlay2.
+func supportsMultipleLowerDir(d string) error {
+	td, err := ioutil.TempDir(d, "multiple-lowerdir-check")
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err := os.RemoveAll(td); err != nil {
+			log.L.WithError(err).Warnf("Failed to remove check directory %v", td)
+		}
+	}()
+
+	for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
+		if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
+			return err
+		}
+	}
+
+	opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", filepath.Join(td, "lower2"), filepath.Join(td, "lower1"), filepath.Join(td, "upper"), filepath.Join(td, "work"))
+	m := mount.Mount{
+		Type:    "overlay",
+		Source:  "overlay",
+		Options: []string{opts},
+	}
+	dest := filepath.Join(td, "merged")
+	if err := m.Mount(dest); err != nil {
+		return errors.Wrap(err, "failed to mount overlay")
+	}
+	if err := mount.UnmountAll(dest, 0); err != nil {
+		log.L.WithError(err).Warnf("Failed to unmount check directory %v", dest)
+	}
+	return nil
+}
+
+// Supported returns nil when the overlayfs is functional on the system with the root directory.
+// Suppported is not called during plugin initialization, but exposed for downstream projects which uses
+// this snapshotter as a library.
+func Supported(root string) error {
+	if err := os.MkdirAll(root, 0700); err != nil {
+		return err
+	}
+	supportsDType, err := fs.SupportsDType(root)
+	if err != nil {
+		return err
+	}
+	if !supportsDType {
+		return 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)
+	}
+	return supportsMultipleLowerDir(root)
+}

snapshots/overlay/check_test.go

@@ -0,0 +1,89 @@
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package overlay
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/containerd/containerd/testutil"
+)
+
+func testOverlaySupported(t testing.TB, expected bool, mkfs ...string) {
+	testutil.RequiresRoot(t)
+	mnt, err := ioutil.TempDir("", "containerd-fs-test-supports-overlay")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(mnt)
+
+	deviceName, cleanupDevice, err := testutil.NewLoopback(100 << 20) // 100 MB
+	if err != nil {
+		t.Fatal(err)
+	}
+	if out, err := exec.Command(mkfs[0], append(mkfs[1:], deviceName)...).CombinedOutput(); err != nil {
+		// not fatal
+		t.Skipf("could not mkfs (%v) %s: %v (out: %q)", mkfs, deviceName, err, string(out))
+	}
+	if out, err := exec.Command("mount", deviceName, mnt).CombinedOutput(); err != nil {
+		// not fatal
+		t.Skipf("could not mount %s: %v (out: %q)", deviceName, err, string(out))
+	}
+	defer func() {
+		testutil.Unmount(t, mnt)
+		cleanupDevice()
+	}()
+	workload := func() {
+		err = Supported(mnt)
+		if expected && err != nil {
+			t.Fatal(err)
+		}
+		if !expected && err == nil {
+			t.Fatal("error is expected")
+		}
+	}
+	b, ok := t.(*testing.B)
+	if ok {
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			workload()
+		}
+		b.StopTimer()
+	} else {
+		workload()
+	}
+}
+
+func BenchmarkOverlaySupportedOnExt4(b *testing.B) {
+	testOverlaySupported(b, true, "mkfs.ext4", "-F")
+}
+
+func BenchmarkOverlayUnsupportedOnFType0XFS(b *testing.B) {
+	testOverlaySupported(b, false, "mkfs.xfs", "-m", "crc=0", "-n", "ftype=0")
+}
+
+func BenchmarkOverlaySupportedOnFType1XFS(b *testing.B) {
+	testOverlaySupported(b, true, "mkfs.xfs", "-m", "crc=0", "-n", "ftype=1")
+}
+
+func BenchmarkOverlayUnsupportedOnFAT(b *testing.B) {
+	testOverlaySupported(b, false, "mkfs.fat")
+}

testutil/helpers_unix.go

@@ -28,7 +28,7 @@ import (
 )
 
 // Unmount unmounts a given mountPoint and sets t.Error if it fails
-func Unmount(t *testing.T, mountPoint string) {
+func Unmount(t testing.TB, mountPoint string) {
 	t.Log("unmount", mountPoint)
 	err := mount.UnmountAll(mountPoint, umountflags)
 	assert.NilError(t, err)