Android : Android Canvas.ClipPath

I wanna clip a circle region, but somehow I got a rectangle, not a circle. And here is my code:

protected boolean drawChild(Canvas canvas, View child, long drawTime) {
                mRevealPath.reset();
                mRevealPath.addCircle(mCenterX, mCenterY, mRevealRadius, Path.Direction.CW);
                final int state = canvas.save();
                canvas.clipPath(mRevealPath);
                boolean isInvalidate = super.drawChild(canvas, child, drawTime);
                canvas.restoreToCount(state);
                return isInvalidate;
            }

I add a LinearLayout with a TextView in it as a child to test.