Name
blk_start_request — 
     start request processing on the driver
 
Synopsis
| void blk_start_request ( | struct request * req ); | 
 
Description
   Dequeue req and start timeout timer on it.  This hands off the
   request to the driver.
   
   Block internal functions which don't want to start timer should
   call blk_dequeue_request.
Context
   queue_lock must be held.