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.