block: add API for delaying work/request_fn a little bit

Currently we use plugging for that, but as plugging is going away,
we need an alternative mechanism.

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

2 files changed, 35 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 3cc17e6064d6..e958c7a1e462 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -197,6 +197,32 @@ void blk_dump_rq_flags(struct request *rq, char *msg)
 }
 EXPORT_SYMBOL(blk_dump_rq_flags);
 
+static void blk_delay_work(struct work_struct *work)
+{
+        struct request_queue *q;
+
+        q = container_of(work, struct request_queue, delay_work.work);
+        spin_lock_irq(q->queue_lock);
+        q->request_fn(q);
+        spin_unlock_irq(q->queue_lock);
+}
+
+/**
+ * blk_delay_queue - restart queueing after defined interval
+ * @q:          The &struct request_queue in question
+ * @msecs:      Delay in msecs
+ *
+ * Description:
+ *   Sometimes queueing needs to be postponed for a little while, to allow
+ *   resources to come back. This function will make sure that queueing is
+ *   restarted around the specified time.
+ */
+void blk_delay_queue(struct request_queue *q, unsigned long msecs)
+{
+        schedule_delayed_work(&q->delay_work, msecs_to_jiffies(msecs));
+}
+EXPORT_SYMBOL(blk_delay_queue);
+
 /*
  * "plug" the device if there are no outstanding requests: this will
  * force the transfer to start only after we have put all the requests
@@ -363,6 +389,7 @@ EXPORT_SYMBOL(blk_start_queue);
 void blk_stop_queue(struct request_queue *q)
 {
         blk_remove_plug(q);
+        cancel_delayed_work(&q->delay_work);
         queue_flag_set(QUEUE_FLAG_STOPPED, q);
 }
 EXPORT_SYMBOL(blk_stop_queue);
@@ -387,6 +414,7 @@ void blk_sync_queue(struct request_queue *q)
         del_timer_sync(&q->timeout);
         cancel_work_sync(&q->unplug_work);
         throtl_shutdown_timer_wq(q);
+        cancel_delayed_work_sync(&q->delay_work);
 }
 EXPORT_SYMBOL(blk_sync_queue);
 
@@ -534,6 +562,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
         INIT_LIST_HEAD(&q->flush_queue[1]);
         INIT_LIST_HEAD(&q->flush_data_in_flight);
         INIT_WORK(&q->unplug_work, blk_unplug_work);
+        INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);
 
         kobject_init(&q->kobj, &blk_queue_ktype);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e3ee74fc5903..f55b2a8b6610 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -300,6 +300,11 @@ struct request_queue
         unsigned long           unplug_delay;   /* After this many jiffies */
         struct work_struct      unplug_work;
 
+        /*
+         * Delayed queue handling
+         */
+        struct delayed_work     delay_work;
+
         struct backing_dev_info backing_dev_info;
 
         /*
@@ -677,6 +682,7 @@ extern int blk_insert_cloned_request(struct request_queue *q,
 extern void blk_plug_device(struct request_queue *);
 extern void blk_plug_device_unlocked(struct request_queue *);
 extern int blk_remove_plug(struct request_queue *);
+extern void blk_delay_queue(struct request_queue *, unsigned long);
 extern void blk_recount_segments(struct request_queue *, struct bio *);
 extern int scsi_cmd_ioctl(struct request_queue *, struct gendisk *, fmode_t,
                           unsigned int, void __user *);