Ignore error when xattr data is not available

When the underlying filesystem is overlayfs, it is possible that xattrs
are present but without the data. So check for this case specifically
and ignore it.

Signed-off-by: Ramkumar Chinchani <[email protected]>

oci/layer/tar_generate.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"syscall"
 
 	"github.com/apex/log"
 	"github.com/opencontainers/umoci/pkg/fseval"
@@ -217,6 +218,14 @@ func (tg *tarGenerator) AddFile(name, path string) error {
 			// XXX: I'm not sure if we're unprivileged whether Lgetxattr can
 			//      fail with EPERM. If it can, we should ignore it (like when
 			//      we try to clear xattrs).
+
+			// in case of overlayfs, we may not get the xattr data itself,
+			// so ignore if this particular error code
+			if err == syscall.ENODATA {
+				log.Warnf("unable to get xattr: %s", name)
+				continue
+			}
+
 			return errors.Wrapf(err, "get xattr: %s", name)
 		}
 		// https://golang.org/issues/20698 -- We don't just error out here