generic_unplug_device - fire a request queue
void generic_unplug_device (request_queue_t * q);
q The &request_queue_t in question
Linux uses plugging to build bigger requests queues before letting the device have at them. If a queue is plugged, the I/O scheduler is still adding and merging requests on the queue. Once the queue gets unplugged, the request_fn defined for the queue is invoked and transfers started.