diff --git a/lxd/storage/drivers/interface.go b/lxd/storage/drivers/interface.go
index <HASH>..<HASH> 100644
--- a/lxd/storage/drivers/interface.go
+++ b/lxd/storage/drivers/interface.go
@@ -57,9 +57,8 @@ type Driver interface {
 	SetVolumeQuota(vol Volume, size string, op *operations.Operation) error
 	GetVolumeDiskPath(vol Volume) (string, error)
 
-	// MountVolume mounts a storage volume, returns true if we caused a new mount, false if
-	// already mounted.
-	MountVolume(vol Volume, op *operations.Operation) (bool, error)
+	// MountVolume mounts a storage volume (if not mounted) and increments reference counter.
+	MountVolume(vol Volume, op *operations.Operation) error
 
 	// MountVolumeSnapshot mounts a storage volume snapshot as readonly, returns true if we
 	// caused a new mount, false if already mounted.
lxd/storage/drivers/interface: Removes "our mount" bool return value from MountVolume

Ref counting keeps track of whether an unmount should proceed or not, so no need for indicating to caller whether they need to unmount or not.