1 files changed, 28 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index c66333d8e48d..b2d0ac8b760e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2100,6 +2100,34 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
                 rq->rq_disk = bio->bi_bdev->bd_disk;
 }
 
+/**
+ * blk_lld_busy - Check if underlying low-level drivers of a device are busy
+ * @q : the queue of the device being checked
+ *
+ * Description:
+ *    Check if underlying low-level drivers of a device are busy.
+ *    If the drivers want to export their busy state, they must set own
+ *    exporting function using blk_queue_lld_busy() first.
+ *
+ *    Basically, this function is used only by request stacking drivers
+ *    to stop dispatching requests to underlying devices when underlying
+ *    devices are busy.  This behavior helps more I/O merging on the queue
+ *    of the request stacking driver and prevents I/O throughput regression
+ *    on burst I/O load.
+ *
+ * Return:
+ *    0 - Not busy (The request stacking driver should dispatch request)
+ *    1 - Busy (The request stacking driver should stop dispatching request)
+ */
+int blk_lld_busy(struct request_queue *q)
+{
+        if (q->lld_busy_fn)
+                return q->lld_busy_fn(q);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(blk_lld_busy);
+
 int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
 {
         return queue_work(kblockd_workqueue, work);