Set<String> getUsersWithNamespaceReadAction(String namespace, boolean includeGlobal)
    throws IOException {
    Set<String> users =
      getUsersWithReadAction(PermissionStorage.getNamespacePermissions(conf, namespace));
    if (includeGlobal) {
      users.addAll(getUsersWithGlobalReadAction());
    }
    return users;
  }
Return users with namespace read permission
@param namespace     the namespace
@param includeGlobal true if include users with global read action
@return users with namespace read permission
@throws IOException if an error occurred
hbase-server/src/main/java/org/apache/hadoop/hbase/security/access/SnapshotScannerHDFSAclHelper.java