rbd: handle when krbdFeatures is zero

krbdFeatures is set to zero when kernel version < 3.8, i.e. in  case where
/sys/bus/rbd/supported_features is absent and we are unable to prepare
the krbd attributes based on kernel version.

When krbdFeatures is set to zero fallback to NBD only when autofallback
is turned ON.

Fixes: #2678
Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

internal/rbd/nodeserver.go

@@ -144,6 +144,7 @@ func healerStageTransaction(ctx context.Context, cr *util.Credentials, volOps *r
 // this function also receive the credentials and secrets args as it differs in its data.
 // The credentials are used directly by functions like voljournal.Connect() and other functions
 // like genVolFromVolumeOptions() make use of secrets.
+// nolint:gocyclo,cyclop // reduce complexity
 func populateRbdVol(
 	ctx context.Context,
 	req *csi.NodeStageVolumeRequest,
@@ -241,8 +242,15 @@ func populateRbdVol(
 		return nil, status.Error(codes.Internal, err.Error())
 	}
 
-	if rv.Mounter == rbdDefaultMounter &&
+	features := strings.Join(rv.ImageFeatureSet.Names(), ",")
-		!isKrbdFeatureSupported(ctx, strings.Join(rv.ImageFeatureSet.Names(), ",")) {
+	isFeatureExist, err := isKrbdFeatureSupported(ctx, features)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		log.ErrorLog(ctx, "failed checking krbd features %q: %v", features, err)
+
+		return nil, status.Error(codes.Internal, err.Error())
+	}
+
+	if rv.Mounter == rbdDefaultMounter && !isFeatureExist {
 		if !parseBoolOption(ctx, req.GetVolumeContext(), tryOtherMounters, false) {
 			log.ErrorLog(ctx, "unsupported krbd Feature, set `tryOtherMounters:true` or fix krbd driver")
 			err = errors.New("unsupported krbd Feature")

internal/rbd/rbd_util.go

@@ -328,7 +328,12 @@ func HexStringToInteger(hexString string) (uint, error) {
 
 // isKrbdFeatureSupported checks if a given Image Feature is supported by krbd
 // driver or not.
-func isKrbdFeatureSupported(ctx context.Context, imageFeatures string) bool {
+func isKrbdFeatureSupported(ctx context.Context, imageFeatures string) (bool, error) {
+	// return false when /sys/bus/rbd/supported_features is absent and we are
+	// not in a position to prepare krbd feature attributes, i.e. if kernel <= 3.8
+	if krbdFeatures == 0 {
+		return false, os.ErrNotExist
+	}
 	arr := strings.Split(imageFeatures, ",")
 	log.UsefulLog(ctx, "checking for ImageFeatures: %v", arr)
 	imageFeatureSet := librbd.FeatureSetFromNames(arr)
@@ -343,7 +348,7 @@ func isKrbdFeatureSupported(ctx context.Context, imageFeatures string) bool {
 		}
 	}
 
-	return supported
+	return supported, nil
 }
 
 // Connect an rbdVolume to the Ceph cluster.

internal/rbd/rbd_util_test.go

@@ -18,6 +18,7 @@ package rbd
 
 import (
 	"context"
+	"errors"
 	"io/ioutil"
 	"os"
 	"strings"
@@ -346,8 +347,13 @@ func TestIsKrbdFeatureSupported(t *testing.T) {
 			if err != nil {
 				t.Errorf("HexStringToInteger(%s) failed", krbdSupportedFeaturesAttr)
 			}
-			supported := isKrbdFeatureSupported(ctx, tc.featureName)
+			// In case /sys/bus/rbd/supported_features is absent and we are
-			if supported != tc.isSupported {
+			// not in a position to prepare krbd feature attributes,
+			// isKrbdFeatureSupported returns error ErrNotExist
+			supported, err := isKrbdFeatureSupported(ctx, tc.featureName)
+			if err != nil && !errors.Is(err, os.ErrNotExist) {
+				t.Errorf("isKrbdFeatureSupported(%s) returned error: %v", tc.featureName, err)
+			} else if supported != tc.isSupported {
 				t.Errorf("isKrbdFeatureSupported(%s) returned supported status, expected: %t, got: %t",
 					tc.featureName, tc.isSupported, supported)
 			}