Man page 9 : bio_copy_user

bio_copy_user - copy user data to bio

struct bio * bio_copy_user(struct request_queue *  q , struct rq_map_data *  map_data , unsigned long  uaddr , unsigned int  len , int  write_to_vm , gfp_t  gfp_mask );

q
    destination block queue

map_data
    pointer to the rq_map_data holding pages (if necessary)

uaddr
    start of user address

len
    length in bytes

write_to_vm
    bool indicating writing to pages or not

gfp_mask
    memory allocation flags

Prepares and returns a bio for indirect user io, bouncing data to/from kernel pages as necessary. Must be paired with call bio_uncopy_user on io completion.