centos man page for blk_queue_start_tag

BLK_QUEUE_START_TAG(9)						   Block Devices					    BLK_QUEUE_START_TAG(9)

NAME
       blk_queue_start_tag - find a free tag and assign it

SYNOPSIS
       int blk_queue_start_tag(struct request_queue * q, struct request * rq);

ARGUMENTS
       q
	   the request queue for the device

       rq
	   the block request that needs tagging

DESCRIPTION
       This can either be used as a stand-alone helper, or possibly be assigned as the queue prep_rq_fn (in which case struct request
       automagically gets a tag assigned). Note that this function assumes that any type of request can be queued! if this is not true for your
       device, you must check the request type before calling this function. The request will also be removed from the request queue, so it's the
       drivers responsibility to readd it if it should need to be restarted for some reason.

NOTES
       queue lock must be held.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						    BLK_QUEUE_START_TAG(9)