centos man page for blk_rq_map_user

BLK_RQ_MAP_USER(9)						   Block Devices						BLK_RQ_MAP_USER(9)

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

SYNOPSIS
       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);

ARGUMENTS
       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

DESCRIPTION
       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.

NOTE
       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.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							BLK_RQ_MAP_USER(9)