overlay: use function to check for overlay-based mounts

Factorize code that check for an overlay mount type by using a function
instead.

This will allow supporting other overlay-based mount types more easily
in the future (for example fuse-overlayfs).

Signed-off-by: Alexis Murzeau <[email protected]>

Author: amurzeau

cache/manager_test.go

@@ -45,6 +45,7 @@ import (
 	"github.com/moby/buildkit/util/contentutil"
 	"github.com/moby/buildkit/util/iohelper"
 	"github.com/moby/buildkit/util/leaseutil"
+	"github.com/moby/buildkit/util/overlay"
 	"github.com/moby/buildkit/util/winlayers"
 	digest "github.com/opencontainers/go-digest"
 	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
@@ -2701,7 +2702,7 @@ func isReadOnly(mnt mount.Mount) bool {
 			hasUpperdir = true
 		}
 	}
-	if mnt.Type == "overlay" {
+	if overlay.IsOverlayMountType(mnt) {
 		return !hasUpperdir
 	}
 	return false

cache/refs.go

@@ -27,6 +27,7 @@ import (
 	"github.com/moby/buildkit/util/compression"
 	"github.com/moby/buildkit/util/flightcontrol"
 	"github.com/moby/buildkit/util/leaseutil"
+	"github.com/moby/buildkit/util/overlay"
 	"github.com/moby/buildkit/util/progress"
 	rootlessmountopts "github.com/moby/buildkit/util/rootless/mountopts"
 	"github.com/moby/buildkit/util/winlayers"
@@ -1513,7 +1514,7 @@ func (m *readOnlyMounter) Mount() ([]mount.Mount, func() error, error) {
 		return nil, nil, err
 	}
 	for i, m := range mounts {
-		if m.Type == "overlay" {
+		if overlay.IsOverlayMountType(m) {
 			mounts[i].Options = readonlyOverlay(m.Options)
 			continue
 		}
@@ -1623,7 +1624,7 @@ func (sm *sharableMountable) Mount() (_ []mount.Mount, _ func() error, retErr er
 		}()
 		var isOverlay bool
 		for _, m := range mounts {
-			if m.Type == "overlay" {
+			if overlay.IsOverlayMountType(m) {
 				isOverlay = true
 				break
 			}

snapshot/diffapply_unix.go

@@ -167,8 +167,7 @@ func applierFor(dest Mountable, tryCrossSnapshotLink, userxattr bool) (_ *applie
 	}
 	mnt := mnts[0]
 
-	switch mnt.Type {
-	case "overlay":
+	if overlay.IsOverlayMountType(mnt) {
 		for _, opt := range mnt.Options {
 			if strings.HasPrefix(opt, "upperdir=") {
 				a.root = strings.TrimPrefix(opt, "upperdir=")
@@ -183,9 +182,9 @@ func applierFor(dest Mountable, tryCrossSnapshotLink, userxattr bool) (_ *applie
 			return nil, errors.Errorf("could not find lowerdir in mount options %v", mnt.Options)
 		}
 		a.createWhiteoutDelete = true
-	case "bind", "rbind":
+	} else if mnt.Type == "bind" || mnt.Type == "rbind" {
 		a.root = mnt.Source
-	default:
+	} else {
 		mnter := LocalMounter(dest)
 		root, err := mnter.Mount()
 		if err != nil {
@@ -570,10 +569,9 @@ func differFor(lowerMntable, upperMntable Mountable) (_ *differ, rerr error) {
 	}
 
 	if len(upperMnts) == 1 {
-		switch upperMnts[0].Type {
-		case "bind", "rbind":
+		if upperMnts[0].Type == "bind" || upperMnts[0].Type == "rbind" {
 			d.upperBindSource = upperMnts[0].Source
-		case "overlay":
+		} else if overlay.IsOverlayMountType(upperMnts[0]) {
 			overlayDirs, err := overlay.GetOverlayLayers(upperMnts[0])
 			if err != nil {
 				return nil, errors.Wrapf(err, "failed to get overlay layers from mount %+v", upperMnts[0])

snapshot/snapshotter.go

@@ -167,6 +167,8 @@ func setRedirectDir(mounts []mount.Mount, redirectDirOption string) (ret []mount
 		return mounts
 	}
 	for _, m := range mounts {
+		// Replace redirect_dir options, but only for overlay.
+		// redirect_dir is not supported by fuse-overlayfs.
 		if m.Type == "overlay" {
 			var opts []string
 			for _, o := range m.Options {

snapshot/snapshotter_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/containerd/continuity/fs/fstest"
 	"github.com/moby/buildkit/identity"
 	"github.com/moby/buildkit/util/leaseutil"
+	overlayutil "github.com/moby/buildkit/util/overlay"
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/require"
 	bolt "go.etcd.io/bbolt"
@@ -602,7 +603,7 @@ func pathCallback[T any](ctx context.Context, t *testing.T, sn *mergeSnapshotter
 	require.Len(t, mounts, 1)
 	mnt := mounts[0]
 
-	if mnt.Type == "overlay" {
+	if overlayutil.IsOverlayMountType(mnt) {
 		var upperdir string
 		var lowerdirs []string
 		for _, opt := range mnt.Options {

util/overlay/overlay.go

@@ -0,0 +1,8 @@
+package overlay
+
+import "github.com/containerd/containerd/mount"
+
+// IsOverlayMountType returns true if the mount type is overlay-based
+func IsOverlayMountType(mnt mount.Mount) bool {
+	return mnt.Type == "overlay"
+}

util/overlay/overlay_linux.go

@@ -38,24 +38,23 @@ func GetUpperdir(lower, upper []mount.Mount) (string, error) {
 		// Get layer directories of lower snapshot
 		var lowerlayers []string
 		lowerM := lower[0]
-		switch lowerM.Type {
-		case "bind":
+		if lowerM.Type == "bind" {
 			// lower snapshot is a bind mount of one layer
 			lowerlayers = []string{lowerM.Source}
-		case "overlay":
+		} else if IsOverlayMountType(lowerM) {
 			// lower snapshot is an overlay mount of multiple layers
 			var err error
 			lowerlayers, err = GetOverlayLayers(lowerM)
 			if err != nil {
 				return "", err
 			}
-		default:
+		} else {
 			return "", errors.Errorf("cannot get layer information from mount option (type = %q)", lowerM.Type)
 		}
 
 		// Get layer directories of upper snapshot
 		upperM := upper[0]
-		if upperM.Type != "overlay" {
+		if !IsOverlayMountType(upperM) {
 			return "", errors.Errorf("upper snapshot isn't overlay mounted (type = %q)", upperM.Type)
 		}
 		upperlayers, err := GetOverlayLayers(upperM)