Drop overlay attributes before creating squashfs.

The overlay attributes [1] have given us some grief [2].
They don't seem to provide benefit.  We are keeping the overlay.opaque
values, but drop everything else in *.overlay.* namespace.

[1] https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html
[2] vasi/squashfuse#78

go.mod

@@ -30,6 +30,7 @@ require (
 	github.com/opencontainers/runc v1.1.2 // indirect
 	github.com/opencontainers/umoci v0.4.8-0.20220412065115-12453f247749
 	github.com/pkg/errors v0.9.1
+	github.com/pkg/xattr v0.4.9
 	github.com/prometheus/common v0.32.1 // indirect
 	github.com/smartystreets/assertions v1.0.1 // indirect
 	github.com/smartystreets/goconvey v1.6.4
@@ -41,7 +42,7 @@ require (
 	go.mozilla.org/pkcs7 v0.0.0-20210826202110-33d05740a352 // indirect
 	golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871 // indirect
 	golang.org/x/net v0.0.0-20220225172249-27dd8689420f // indirect
-	golang.org/x/sys v0.0.0-20220227234510-4e6760a101f9
+	golang.org/x/sys v0.0.0-20220408201424-a24fb2fb8a0f
 	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211
 	google.golang.org/genproto v0.0.0-20220303160752-862486edd9cc // indirect
 	gopkg.in/yaml.v2 v2.4.0

go.sum

@@ -1247,6 +1247,8 @@ github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/sftp v1.10.1/go.mod h1:lYOWFsE0bwd1+KfKJaKeuokY15vzFx25BLbzYYoAxZI=
+github.com/pkg/xattr v0.4.9 h1:5883YPCtkSd8LFbs13nXplj9g9tlrwoJRjgpgMu1/fE=
+github.com/pkg/xattr v0.4.9/go.mod h1:di8WF84zAKk8jzR1UBTEWh9AUlIZZ7M/JNt8e9B6ktU=
 github.com/pmezard/go-difflib v0.0.0-20151028094244-d8ed2627bdf0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
@@ -1908,8 +1910,8 @@ golang.org/x/sys v0.0.0-20211025201205-69cdffdb9359/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20211109184856-51b60fd695b3/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20211116061358-0a5406a5449c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220227234510-4e6760a101f9 h1:nhht2DYV/Sn3qOayu8lM+cU1ii9sTLUeBQwQQfUHtrs=
-golang.org/x/sys v0.0.0-20220227234510-4e6760a101f9/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220408201424-a24fb2fb8a0f h1:8w7RhxzTVgUzw/AH/9mUV5q0vMgy40SQRursCcfmkCw=
+golang.org/x/sys v0.0.0-20220408201424-a24fb2fb8a0f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=

overlay/pack.go

@@ -4,9 +4,11 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path"
+	"path/filepath"
 	"runtime"
 	"strings"
 	"time"
@@ -19,6 +21,7 @@ import (
 	"github.com/opencontainers/umoci/oci/casext"
 	"github.com/opencontainers/umoci/oci/layer"
 	"github.com/pkg/errors"
+	"github.com/pkg/xattr"
 	"github.com/project-stacker/stacker/lib"
 	"github.com/project-stacker/stacker/log"
 	stackeroci "github.com/project-stacker/stacker/oci"
@@ -316,6 +319,44 @@ func ociPutBlob(blob io.ReadCloser, config types.StackerConfig, layerMediaType s
 	return desc, nil
 }
 
+func stripOverlayAttrs(path string) error {
+	attrs, err := xattr.LList(path)
+	if err != nil {
+		return err
+	}
+	const match = ".overlay."
+	const opaque = match + "opaque"
+
+	dropped := []string{}
+	for _, attr := range attrs {
+		if !strings.Contains(attr, match) {
+			continue
+		}
+		if strings.HasSuffix(attr, opaque) {
+			continue
+		}
+		if err := xattr.LRemove(path, attr); err != nil {
+			return errors.Errorf("%s: failed to remove attr %s: %v", path, attr, err)
+		}
+		dropped = append(dropped, attr)
+	}
+
+	if len(dropped) != 0 {
+		log.Debugf("%s: dropped overlay attrs: %s", path, strings.Join(dropped, ","))
+	}
+	return nil
+}
+
+func stripOverlayAttrsUnder(dirPath string) error {
+	return fs.WalkDir(os.DirFS(dirPath), ".",
+		func(path string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+			return stripOverlayAttrs(filepath.Join(dirPath, path))
+		})
+}
+
 func generateLayer(config types.StackerConfig, oci casext.Engine, mutators []*mutate.Mutator, name string, layerTypes []types.LayerType) (bool, error) {
 	dir := path.Join(config.RootFSDir, name, "overlay")
 	ents, err := ioutil.ReadDir(dir)
@@ -357,6 +398,10 @@ func generateLayer(config types.StackerConfig, oci casext.Engine, mutators []*mu
 		EmptyLayer: false,
 	}
 
+	if err := stripOverlayAttrsUnder(dir); err != nil {
+		return false, err
+	}
+
 	descs := []ispec.Descriptor{}
 	for i, layerType := range layerTypes {
 		mutator := mutators[i]