Map a page of the buffer object into kernel address space. The same restrictions as for kmap and friends apply.
void * dma_buf_kmap (
|struct dma_buf * dmabuf, |
| ||unsigned long page_num|
[in] buffer to map page from.
[in] page in PAGE_SIZE units to map.
This call must always succeed, any necessary preparations that might fail
need to be done in begin_cpu_access.