centos man page for blk_update_request

BLK_UPDATE_REQUEST(9)						   Block Devices					     BLK_UPDATE_REQUEST(9)

NAME
       blk_update_request - Special helper function for request stacking drivers

SYNOPSIS
       bool blk_update_request(struct request * req, int error, unsigned int nr_bytes);

ARGUMENTS
       req
	   the request being processed

       error
	   0 for success, < 0 for error

       nr_bytes
	   number of bytes to complete req

DESCRIPTION
       Ends I/O on a number of bytes attached to req, but doesn't complete the request structure even if req doesn't have leftover. If req has
       leftover, sets it up for the next range of segments.

       This special helper function is only for request stacking drivers (e.g. request-based dm) so that they can handle partial completion.
       Actual device drivers should use blk_end_request instead.

       Passing the result of blk_rq_bytes as nr_bytes guarantees false return from this function.

RETURN
       false - this request doesn't have any more data true - this request has more data

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						     BLK_UPDATE_REQUEST(9)