Man page 9 : blk_rq_map_kern

blk_rq_map_kern - map kernel data to a request, for REQ_TYPE_BLOCK_PC usage

int blk_rq_map_kern(struct request_queue *  q , struct request *  rq , void *  kbuf , unsigned int  len , gfp_t  gfp_mask );

q
    request queue where request should be inserted

rq
    request to fill

kbuf
    the kernel buffer

len
    length of user data

gfp_mask
    memory allocation flags

Data will be mapped directly if possible. Otherwise a bounce buffer is used. Can be called multple times to append multple buffers.