create table emp(empid number,ename varchar2(10),deptno number)

CREATE OR REPLACE FUNCTION no_dept10(
      p_schema  IN VARCHAR2,
      p_object  IN VARCHAR2)
      RETURN VARCHAR2
    AS
    BEGIN
      RETURN 'deptno != 10';
    END;

Grant select on emp to X1;

SQL> BEGIN
  2        DBMS_RLS.add_policy
  3           (object_schema    => 'X1',
  4            object_name      => 'EMP',
  5            policy_name      => 'quickstart',
  6            policy_function  => 'no_dept10');
  7      END;
  8  /

BEGIN
      DBMS_RLS.add_policy
         (object_schema    => 'X1',
          object_name      => 'EMP',
          policy_name      => 'quickstart',
          policy_function  => 'no_dept10');
    END;

ORA-00942: table or view does not exist
ORA-06512: at "SYS.DBMS_RLS", line 20
ORA-06512: at line 2

CREATE OR REPLACE FUNCTION no_dept10(
      p_schema  IN VARCHAR2,
      p_object  IN VARCHAR2)
      RETURN VARCHAR2
    AS
    BEGIN
    if p_schema = 'X1' then
       return 'deptno != 10';
    else
       return null;
    end if;
    END;

select * from X1_DBA.emp 

X1_DBA@orcl_11gR2> create or replace function x1_dba.no_dept10
  2    (p_schema in varchar2,
  3  	p_object in varchar2)
  4    return	    varchar2
  5  as
  6  begin
  7    if user = 'X1' then
  8  	 return 'deptno != 10';
  9    else
 10  	 return null;
 11    end if;
 12  end;
 13  /

Function created.

X1_DBA@orcl_11gR2> show errors
No errors.
X1_DBA@orcl_11gR2> begin
  2    dbms_rls.add_policy
  3  	 (object_schema   => 'X1_DBA',
  4  	  object_name	  => 'EMP',
  5  	  policy_name	  => 'quickstart',
  6  	  policy_function => 'no_dept10');
  7  end;
  8  /

PL/SQL procedure successfully completed.

X1_DBA@orcl_11gR2> select * from x1_dba.emp
  2  /

     EMPID ENAME          DEPTNO
---------- ---------- ----------
      7369 SMITH              20
      7499 ALLEN              30
      7521 WARD               30
      7566 JONES              20
      7654 MARTIN             30
      7698 BLAKE              30
      7782 CLARK              10
      7788 SCOTT              20
      7839 KING               10
      7844 TURNER             30
      7876 ADAMS              20
      7900 JAMES              30
      7902 FORD               20
      7934 MILLER             10

14 rows selected.

X1_DBA@orcl_11gR2> grant select on x1_dba.emp to x1
  2  /

Grant succeeded.

X1_DBA@orcl_11gR2> connect x1/x1
Connected.
X1@orcl_11gR2> select * from x1_dba.emp
  2  /

     EMPID ENAME          DEPTNO
---------- ---------- ----------
      7369 SMITH              20
      7499 ALLEN              30
      7521 WARD               30
      7566 JONES              20
      7654 MARTIN             30
      7698 BLAKE              30
      7788 SCOTT              20
      7844 TURNER             30
      7876 ADAMS              20
      7900 JAMES              30
      7902 FORD               20

11 rows selected.

X1@orcl_11gR2>