Merge pull request #40462 from AkihiroSuda/cherrypick-40210-1903

[19.03 backport] overlay[2]: rm extra checks in init 
Upstream-commit: 4ac62b478d539d2539e49d7c710eaea482e47293
Component: engine

Author: AkihiroSuda

components/engine/daemon/graphdriver/devmapper/deviceset.go

@@ -540,8 +540,14 @@ func xfsSupported() error {
 		return err // error text is descriptive enough
 	}
 
-	// Check if kernel supports xfs filesystem or not.
-	exec.Command("modprobe", "xfs").Run()
+	mountTarget, err := ioutil.TempDir("", "supportsXFS")
+	if err != nil {
+		return errors.Wrapf(err, "error checking for xfs support")
+	}
+
+	/* The mounting will fail--after the module has been loaded.*/
+	defer os.RemoveAll(mountTarget)
+	unix.Mount("none", mountTarget, "xfs", 0, "")
 
 	f, err := os.Open("/proc/filesystems")
 	if err != nil {

components/engine/daemon/graphdriver/overlay/overlay.go

@@ -3,12 +3,10 @@
 package overlay // import "github.com/docker/docker/daemon/graphdriver/overlay"
 
 import (
-	"bufio"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path"
 	"path/filepath"
 	"strconv"
@@ -124,10 +122,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, err
 	}
 
-	if err := supportsOverlay(); err != nil {
-		return nil, graphdriver.ErrNotSupported
-	}
-
 	// Perform feature detection on /var/lib/docker/overlay if it's an existing directory.
 	// This covers situations where /var/lib/docker/overlay is a mount, and on a different
 	// filesystem than /var/lib/docker.
@@ -137,18 +131,9 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		testdir = filepath.Dir(testdir)
 	}
 
-	fsMagic, err := graphdriver.GetFSMagic(testdir)
-	if err != nil {
-		return nil, err
-	}
-	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
-		backingFs = fsName
-	}
-
-	switch fsMagic {
-	case graphdriver.FsMagicAufs, graphdriver.FsMagicBtrfs, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs:
-		logrus.WithField("storage-driver", "overlay").Errorf("'overlay' is not supported over %s", backingFs)
-		return nil, graphdriver.ErrIncompatibleFS
+	if err := overlayutils.SupportsOverlay(testdir, false); err != nil {
+		logrus.WithField("storage-driver", "overlay").Error(err)
+		return nil, graphdriver.ErrNotSupported
 	}
 
 	supportsDType, err := fsutils.SupportsDType(testdir)
@@ -200,27 +185,6 @@ func parseOptions(options []string) (*overlayOptions, error) {
 	return o, nil
 }
 
-func supportsOverlay() error {
-	// We can try to modprobe overlay first before looking at
-	// proc/filesystems for when overlay is supported
-	exec.Command("modprobe", "overlay").Run()
-
-	f, err := os.Open("/proc/filesystems")
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	s := bufio.NewScanner(f)
-	for s.Scan() {
-		if s.Text() == "nodev\toverlay" {
-			return nil
-		}
-	}
-	logrus.WithField("storage-driver", "overlay").Error("'overlay' not found as a supported filesystem on this host. Please ensure kernel is new enough and has overlay support loaded.")
-	return graphdriver.ErrNotSupported
-}
-
 func (d *Driver) String() string {
 	return "overlay"
 }

components/engine/daemon/graphdriver/overlay2/check.go

@@ -99,35 +99,3 @@ func doesSupportNativeDiff(d string) error {
 
 	return nil
 }
-
-// supportsMultipleLowerDir checks if the system supports multiple lowerdirs,
-// which is required for the overlay2 driver. 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.
-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 {
-			logger.Warnf("Failed to remove check directory %v: %v", td, err)
-		}
-	}()
-
-	for _, dir := range []string{"lower1", "lower2", "upper", workDirName, mergedDirName} {
-		if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
-			return err
-		}
-	}
-
-	opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", path.Join(td, "lower2"), path.Join(td, "lower1"), path.Join(td, "upper"), path.Join(td, workDirName))
-	if err := unix.Mount("overlay", filepath.Join(td, mergedDirName), "overlay", 0, opts); err != nil {
-		return errors.Wrap(err, "failed to mount overlay")
-	}
-	if err := unix.Unmount(filepath.Join(td, mergedDirName), 0); err != nil {
-		logger.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, mergedDirName), err)
-	}
-	return nil
-}

components/engine/daemon/graphdriver/overlay2/overlay.go

@@ -3,14 +3,12 @@
 package overlay2 // import "github.com/docker/docker/daemon/graphdriver/overlay2"
 
 import (
-	"bufio"
 	"context"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path"
 	"path/filepath"
 	"strconv"
@@ -29,7 +27,6 @@ import (
 	"github.com/docker/docker/pkg/locker"
 	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/parsers"
-	"github.com/docker/docker/pkg/parsers/kernel"
 	"github.com/docker/docker/pkg/system"
 	"github.com/docker/go-units"
 	rsystem "github.com/opencontainers/runc/libcontainer/system"
@@ -134,16 +131,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, err
 	}
 
-	if err := supportsOverlay(); err != nil {
-		return nil, graphdriver.ErrNotSupported
-	}
-
-	// require kernel 4.0.0 to ensure multiple lower dirs are supported
-	v, err := kernel.GetKernelVersion()
-	if err != nil {
-		return nil, err
-	}
-
 	// Perform feature detection on /var/lib/docker/overlay2 if it's an existing directory.
 	// This covers situations where /var/lib/docker/overlay2 is a mount, and on a different
 	// filesystem than /var/lib/docker.
@@ -153,40 +140,11 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		testdir = filepath.Dir(testdir)
 	}
 
-	fsMagic, err := graphdriver.GetFSMagic(testdir)
-	if err != nil {
-		return nil, err
-	}
-	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
-		backingFs = fsName
-	}
-
-	switch fsMagic {
-	case graphdriver.FsMagicAufs, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs:
-		logger.Errorf("'overlay2' is not supported over %s", backingFs)
-		return nil, graphdriver.ErrIncompatibleFS
-	case graphdriver.FsMagicBtrfs:
-		// Support for OverlayFS on BTRFS was added in kernel 4.7
-		// See https://btrfs.wiki.kernel.org/index.php/Changelog
-		if kernel.CompareKernelVersion(*v, kernel.VersionInfo{Kernel: 4, Major: 7, Minor: 0}) < 0 {
-			if !opts.overrideKernelCheck {
-				logger.Errorf("'overlay2' requires kernel 4.7 to use on %s", backingFs)
-				return nil, graphdriver.ErrIncompatibleFS
-			}
-			logger.Warn("Using pre-4.7.0 kernel for overlay2 on btrfs, may require kernel update")
-		}
+	if err := overlayutils.SupportsOverlay(testdir, true); err != nil {
+		logger.Error(err)
+		return nil, graphdriver.ErrNotSupported
 	}
 
-	if kernel.CompareKernelVersion(*v, kernel.VersionInfo{Kernel: 4, Major: 0, Minor: 0}) < 0 {
-		if opts.overrideKernelCheck {
-			logger.Warn("Using pre-4.0.0 kernel for overlay2, mount failures may require kernel update")
-		} else {
-			if err := supportsMultipleLowerDir(testdir); err != nil {
-				logger.Debugf("Multiple lower dirs not supported: %v", err)
-				return nil, graphdriver.ErrNotSupported
-			}
-		}
-	}
 	supportsDType, err := fsutils.SupportsDType(testdir)
 	if err != nil {
 		return nil, err
@@ -275,27 +233,6 @@ func parseOptions(options []string) (*overlayOptions, error) {
 	return o, nil
 }
 
-func supportsOverlay() error {
-	// We can try to modprobe overlay first before looking at
-	// proc/filesystems for when overlay is supported
-	exec.Command("modprobe", "overlay").Run()
-
-	f, err := os.Open("/proc/filesystems")
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	s := bufio.NewScanner(f)
-	for s.Scan() {
-		if s.Text() == "nodev\toverlay" {
-			return nil
-		}
-	}
-	logger.Error("'overlay' not found as a supported filesystem on this host. Please ensure kernel is new enough and has overlay support loaded.")
-	return graphdriver.ErrNotSupported
-}
-
 func useNaiveDiff(home string) bool {
 	useNaiveDiffLock.Do(func() {
 		if err := doesSupportNativeDiff(home); err != nil {

components/engine/daemon/graphdriver/overlayutils/overlayutils.go

@@ -4,8 +4,15 @@ package overlayutils // import "github.com/docker/docker/daemon/graphdriver/over
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
 
 	"github.com/docker/docker/daemon/graphdriver"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
 )
 
 // ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.
@@ -23,3 +30,40 @@ func ErrDTypeNotSupported(driver, backingFs string) error {
 
 	return graphdriver.NotSupportedError(msg)
 }
+
+// SupportsOverlay checks if the system supports overlay filesystem
+// by performing an actual overlay mount.
+//
+// checkMultipleLowers parameter enables check for multiple lowerdirs,
+// which is required for the overlay2 driver.
+func SupportsOverlay(d string, checkMultipleLowers bool) error {
+	td, err := ioutil.TempDir(d, "check-overlayfs-support")
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err := os.RemoveAll(td); err != nil {
+			logrus.Warnf("Failed to remove check directory %v: %v", td, err)
+		}
+	}()
+
+	for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
+		if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
+			return err
+		}
+	}
+
+	mnt := filepath.Join(td, "merged")
+	lowerDir := path.Join(td, "lower2")
+	if checkMultipleLowers {
+		lowerDir += ":" + path.Join(td, "lower1")
+	}
+	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, path.Join(td, "upper"), path.Join(td, "work"))
+	if err := unix.Mount("overlay", mnt, "overlay", 0, opts); err != nil {
+		return errors.Wrap(err, "failed to mount overlay")
+	}
+	if err := unix.Unmount(mnt, 0); err != nil {
+		logrus.Warnf("Failed to unmount check directory %v: %v", mnt, err)
+	}
+	return nil
+}