Revert "block: add callback function for unplug notification"

MD can't use this since it really requires us to be able to
keep more than a single piece of state for the unplug. Commit
048c937 added the required support for MD, so get rid of this
now unused code.

This reverts commit f756645.

Conflicts:

	block/blk-core.c

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/blk-core.c

@@ -2674,9 +2674,6 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth,
 {
 	trace_block_unplug(q, depth, !from_schedule);
 	__blk_run_queue(q, from_schedule);
-
-	if (q->unplugged_fn)
-		q->unplugged_fn(q);
 }
 
 static void flush_plug_callbacks(struct blk_plug *plug)

block/blk-settings.c

@@ -790,22 +790,6 @@ void blk_queue_flush(struct request_queue *q, unsigned int flush)
 }
 EXPORT_SYMBOL_GPL(blk_queue_flush);
 
-/**
- * blk_queue_unplugged - register a callback for an unplug event
- * @q:		the request queue for the device
- * @fn:		the function to call
- *
- * Some stacked drivers may need to know when IO is dispatched on an
- * unplug event. By registrering a callback here, they will be notified
- * when someone flushes their on-stack queue plug. The function will be
- * called with the queue lock held.
- */
-void blk_queue_unplugged(struct request_queue *q, unplugged_fn *fn)
-{
-	q->unplugged_fn = fn;
-}
-EXPORT_SYMBOL(blk_queue_unplugged);
-
 static int __init blk_settings_init(void)
 {
 	blk_max_low_pfn = max_low_pfn - 1;

include/linux/blkdev.h

@@ -196,7 +196,6 @@ typedef void (request_fn_proc) (struct request_queue *q);
 typedef int (make_request_fn) (struct request_queue *q, struct bio *bio);
 typedef int (prep_rq_fn) (struct request_queue *, struct request *);
 typedef void (unprep_rq_fn) (struct request_queue *, struct request *);
-typedef void (unplugged_fn) (struct request_queue *);
 
 struct bio_vec;
 struct bvec_merge_data {
@@ -284,7 +283,6 @@ struct request_queue
 	rq_timed_out_fn		*rq_timed_out_fn;
 	dma_drain_needed_fn	*dma_drain_needed;
 	lld_busy_fn		*lld_busy_fn;
-	unplugged_fn		*unplugged_fn;
 
 	/*
 	 * Dispatch queue sorting
@@ -843,7 +841,6 @@ extern void blk_queue_dma_alignment(struct request_queue *, int);
 extern void blk_queue_update_dma_alignment(struct request_queue *, int);
 extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *);
 extern void blk_queue_rq_timed_out(struct request_queue *, rq_timed_out_fn *);
-extern void blk_queue_unplugged(struct request_queue *, unplugged_fn *);
 extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_flush(struct request_queue *q, unsigned int flush);
 extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);