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-rw-r--r--block/blk-core.c28
-rw-r--r--block/blk-settings.c6
2 files changed, 34 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);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 1d0330d0b40a..b21dcdb64151 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -89,6 +89,12 @@ void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
}
EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
+void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
+{
+ q->lld_busy_fn = fn;
+}
+EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
+
/**
* blk_queue_make_request - define an alternate make_request function for a device
* @q: the request queue for the device to be affected