mock_chain
fc->chains[i] = mock_chain(fc->tail,
chain = mock_chain(NULL, f, 1);
chain = mock_chain(NULL, array);
chain = mock_chain(f1, f2);
chain = mock_chain(NULL, array);
c1 = mock_chain(NULL, dma_fence_get(f1));
c2 = mock_chain(c1, dma_fence_get(f2));