struct request * blk_rq_map_user (request_queue_t * q, int rw, void __user * ubuf, unsigned int len);
Data will be mapped directly for zero copy io, if possible. Otherwise a kernel bounce buffer is used.
A matching blk_rq_unmap_user must be issued at the end of io, while still in process context.
The mapped bio may need to be bounced through blk_queue_bounce before being submitted to the device, as pages mapped may be out of reach. It's the callers responsibility to make sure this happens. The original bio must be passed back in to blk_rq_unmap_user for proper unmapping.