suse man page for blk_insert_request

BLK_INSERT_REQUEST(9)						   Block Devices					     BLK_INSERT_REQUEST(9)

NAME
       blk_insert_request - insert a special request into a request queue

SYNOPSIS
       void blk_insert_request(struct request_queue * q, struct request * rq, int at_head, void * data);

ARGUMENTS
       q
	   request queue where request should be inserted

       rq
	   request to be inserted

       at_head
	   insert request at head or tail of queue

       data
	   private data

DESCRIPTION
       Many block devices need to execute commands asynchronously, so they don't block the whole kernel from preemption during request execution.
       This is accomplished normally by inserting aritficial requests tagged as REQ_TYPE_SPECIAL in to the corresponding request queue, and
       letting them be scheduled for actual execution by the request queue.

       We have the option of inserting the head or the tail of the queue. Typically we use the tail for new ioctls and so forth. We use the head
       of the queue for things like a QUEUE_FULL message from a device, or a host that is unable to accept a particular command.

COPYRIGHT
Kernel Hackers Manual 2.6.					     July 2010						     BLK_INSERT_REQUEST(9)