Man page 9 : blk_rq_map_user

blk_rq_map_user - map user data to a request, for REQ_TYPE_BLOCK_PC usage

int blk_rq_map_user(struct request_queue *  q , struct request *  rq , struct rq_map_data *  map_data , void __user *  ubuf , unsigned long  len , gfp_t  gfp_mask );

q
    request queue where request should be inserted

rq
    request structure to fill

map_data
    pointer to the rq_map_data holding pages (if necessary)

ubuf
    the user buffer

len
    length of user data

gfp_mask
    memory allocation flags

Data will be mapped directly for zero copy I/O, if possible. Otherwise a kernel bounce buffer is used.

A matching blk_rq_unmap_user must be issued at the end of I/O, 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. ItAqs the callers responsibility to make sure this happens. The original bio must be passed back in to blk_rq_unmap_user for proper unmapping.