blk_update_request — Special helper function for request stacking drivers
| bool blk_update_request ( | struct request * req, | 
| int error, | |
| unsigned int nr_bytes ); | 
reqthe request being processed
error
     0 for success, < 0 for error
    
nr_bytes
     number of bytes to complete req
    
   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.