Man page 9 : blk_init_queue

blk_init_queue - prepare a request queue for use with a block device

struct request_queue * blk_init_queue(request_fn_proc *  rfn , spinlock_t *  lock );

rfn
    The function to be called to process requests that have been placed on the queue.

lock
    Request queue spin lock

If a block device wishes to use the standard request handling procedures, which sorts requests and coalesces adjacent requests, then it must call blk_init_queue. The function rfn will be called when there are requests on the queue that need to be processed. If the device supports plugging, then rfn may not be called immediately when requests are available on the queue, but may be called at some time later instead. Plugged queues are generally unplugged when a buffer belonging to one of the requests on the queue is needed, or due to memory pressure.

rfn is not required, or even expected, to remove all requests off the queue, but only as many as it can handle at a time. If it does leave requests on the queue, it is responsible for arranging that the requests get dealt with eventually.

The queue spin lock must be held while manipulating the requests on the request queue; this lock will be taken also from interrupt context, so irq disabling is needed for it.

Function returns a pointer to the initialized request queue, or NULL if it didnAqt succeed.

blk_init_queue must be paired with a blk_cleanup_queue call when the block device is deactivated (such as at module unload).