centos man page for blk_queue_make_request

BLK_QUEUE_MAKE_REQUE(9) 					   Block Devices					   BLK_QUEUE_MAKE_REQUE(9)

NAME
       blk_queue_make_request - define an alternate make_request function for a device

SYNOPSIS
       void blk_queue_make_request(struct request_queue * q, make_request_fn * mfn);

ARGUMENTS
       q
	   the request queue for the device to be affected

       mfn
	   the alternate make_request function

DESCRIPTION
       The normal way for struct bios to be passed to a device driver is for them to be collected into requests on a request queue, and then to
       allow the device driver to select requests off that queue when it is ready. This works well for many block devices. However some block
       devices (typically virtual devices such as md or lvm) do not benefit from the processing on the request queue, and are served best by
       having the requests passed directly to them. This can be achieved by providing a function to blk_queue_make_request.

CAVEAT
       The driver that does this *must* be able to deal appropriately with buffers in "highmemory". This can be accomplished by either calling
       __bio_kmap_atomic to get a temporary kernel mapping, or by calling blk_queue_bounce to create a buffer in normal memory.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						   BLK_QUEUE_MAKE_REQUE(9)