dma_buf_unmap_attachment — 
     unmaps and decreases usecount of the buffer;might deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf of dma_buf_ops.
 
| void dma_buf_unmap_attachment ( | struct dma_buf_attachment * attach, | 
| struct sg_table * sg_table, | |
| enum dma_data_direction direction ); |