diff --git a/fs/xfs/libxfs/xfs_rtgroup.h b/fs/xfs/libxfs/xfs_rtgroup.h
index 73cace4d25c7..c0b9f9f2c413 100644
--- a/fs/xfs/libxfs/xfs_rtgroup.h
+++ b/fs/xfs/libxfs/xfs_rtgroup.h
@@ -371,4 +371,19 @@ xfs_rtgs_to_rfsbs(
 	return xfs_groups_to_rfsbs(mp, nr_groups, XG_TYPE_RTG);
 }
 
+/*
+ * Return the "raw" size of a group on the hardware device.  This includes the
+ * daddr gaps present for XFS_SB_FEAT_INCOMPAT_ZONE_GAPS file systems.
+ */
+static inline xfs_rgblock_t
+xfs_rtgroup_raw_size(
+	struct xfs_mount	*mp)
+{
+	struct xfs_groups	*g = &mp->m_groups[XG_TYPE_RTG];
+
+	if (g->has_daddr_gaps)
+		return 1U << g->blklog;
+	return g->blocks;
+}
+
 #endif /* __LIBXFS_RTGROUP_H */