block layer would invoke to pre-build device commands for a given request,
or perform other preparatory processing for the request. This is routine is
called by elv_next_request(), i.e. typically just before servicing a request.
-(The prepare function would not be called for requests that have REQ_DONTPREP
+(The prepare function would not be called for requests that have RQF_DONTPREP
enabled)
Aside: