[PATCH v7 1/4] block: Add support for reinsert a dispatched req

[Tanya Brokhman]

Add support for reinserting a dispatched request back to the
scheduler's internal data structures.
This capability is used by the device driver when it chooses to
interrupt the current request transmission and execute another (more
urgent) pending request. For example: interrupting long write in order
to handle pending read. The device driver re-inserts the
remaining write request back to the scheduler, to be rescheduled
for transmission later on.

Add API for verifying whether the current scheduler
supports reinserting requests mechanism. If reinsert mechanism isn't
supported by the scheduler, this code path will never be activated.

Signed-off-by: Tatyana Brokhman <tlinder@xxxxxxxxxxxxxx>

diff --git a/block/blk-core.c b/block/blk-core.c
index 0852e5d..fe3683c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1183,6 +1183,29 @@ struct request *blk_make_request(struct request_queue *q, struct bio *bio,
 }
 EXPORT_SYMBOL(blk_make_request);
 
+static void __blk_put_back_rq(struct request_queue *q, struct request *rq)
+{
+	blk_delete_timer(rq);
+	blk_clear_rq_complete(rq);
+
+	if (blk_rq_tagged(rq))
+		blk_queue_end_tag(q, rq);
+
+	BUG_ON(blk_queued_rq(rq));
+
+	if (rq->cmd_flags_ext & REQ_URGENT) {
+		/*
+		 * It's not compliant with the design to re-insert
+		 * urgent requests. We want to be able to track this
+		 * down.
+		 */
+		pr_debug("%s(): requeueing/reinserting an URGENT request",
+			__func__);
+		WARN_ON(!q->dispatched_urgent);
+		q->dispatched_urgent = false;
+	}
+}
+
 /**
  * blk_requeue_request - put a request back on queue
  * @q:		request queue where request should be inserted
@@ -1195,19 +1218,45 @@ EXPORT_SYMBOL(blk_make_request);
  */
 void blk_requeue_request(struct request_queue *q, struct request *rq)
 {
-	blk_delete_timer(rq);
-	blk_clear_rq_complete(rq);
+	__blk_put_back_rq(q, rq);
 	trace_block_rq_requeue(q, rq);
-
-	if (blk_rq_tagged(rq))
-		blk_queue_end_tag(q, rq);
-
-	BUG_ON(blk_queued_rq(rq));
-
 	elv_requeue_request(q, rq);
 }
 EXPORT_SYMBOL(blk_requeue_request);
 
+/**
+ * blk_reinsert_request() - Insert a request back to the scheduler
+ * @q:		request queue
+ * @rq:		request to be inserted
+ *
+ * This function inserts the request back to the scheduler as if
+ * it was never dispatched.
+ *
+ * Return: 0 on success, error code on fail
+ */
+int blk_reinsert_request(struct request_queue *q, struct request *rq)
+{
+	__blk_put_back_rq(q, rq);
+	return elv_reinsert_request(q, rq);
+}
+EXPORT_SYMBOL(blk_reinsert_request);
+
+/**
+ * blk_reinsert_req_sup() - check whether the scheduler supports
+ *          reinsertion of requests
+ * @q:		request queue
+ *
+ * Returns true if the current scheduler supports reinserting
+ * request. False otherwise
+ */
+bool blk_reinsert_req_sup(struct request_queue *q)
+{
+	if (unlikely(!q))
+		return false;
+	return q->elevator->type->ops.elevator_reinsert_req_fn ? true : false;
+}
+EXPORT_SYMBOL(blk_reinsert_req_sup);
+
 static void add_acct_request(struct request_queue *q, struct request *rq,
 			     int where)
 {
diff --git a/block/elevator.c b/block/elevator.c
index eba5b04c..e28011b 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -577,6 +577,41 @@ void elv_requeue_request(struct request_queue *q, struct request *rq)
 	__elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
 }
 
+/**
+ * elv_reinsert_request() - Insert a request back to the scheduler
+ * @q:		request queue where request should be inserted
+ * @rq:		request to be inserted
+ *
+ * This function returns the request back to the scheduler to be
+ * inserted as if it was never dispatched
+ *
+ * Return: 0 on success, error code on failure
+ */
+int elv_reinsert_request(struct request_queue *q, struct request *rq)
+{
+	int res;
+
+	if (!q->elevator->type->ops.elevator_reinsert_req_fn)
+		return -EPERM;
+
+	res = q->elevator->type->ops.elevator_reinsert_req_fn(q, rq);
+	if (!res) {
+		/*
+		 * it already went through dequeue, we need to decrement the
+		 * in_flight count again
+		 */
+		if (blk_account_rq(rq)) {
+			q->in_flight[rq_is_sync(rq)]--;
+			if (rq->cmd_flags & REQ_SORTED)
+				elv_deactivate_rq(q, rq);
+		}
+		rq->cmd_flags &= ~REQ_STARTED;
+		q->nr_sorted++;
+	}
+
+	return res;
+}
+
 void elv_drain_elevator(struct request_queue *q)
 {
 	static int printed;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2fdb4a4..968720f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -738,6 +738,8 @@ extern struct request *blk_get_request(struct request_queue *, int, gfp_t);
 extern struct request *blk_make_request(struct request_queue *, struct bio *,
 					gfp_t);
 extern void blk_requeue_request(struct request_queue *, struct request *);
+extern int blk_reinsert_request(struct request_queue *q, struct request *rq);
+extern bool blk_reinsert_req_sup(struct request_queue *q);
 extern void blk_add_request_payload(struct request *rq, struct page *page,
 		unsigned int len);
 extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index acd0312..d703f94 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -23,6 +23,8 @@ typedef void (elevator_bio_merged_fn) (struct request_queue *,
 typedef int (elevator_dispatch_fn) (struct request_queue *, int);
 
 typedef void (elevator_add_req_fn) (struct request_queue *, struct request *);
+typedef int (elevator_reinsert_req_fn) (struct request_queue *,
+					struct request *);
 typedef struct request *(elevator_request_list_fn) (struct request_queue *, struct request *);
 typedef void (elevator_completed_req_fn) (struct request_queue *, struct request *);
 typedef int (elevator_may_queue_fn) (struct request_queue *, int);
@@ -48,6 +50,8 @@ struct elevator_ops
 
 	elevator_dispatch_fn *elevator_dispatch_fn;
 	elevator_add_req_fn *elevator_add_req_fn;
+	elevator_reinsert_req_fn *elevator_reinsert_req_fn;
+
 	elevator_activate_req_fn *elevator_activate_req_fn;
 	elevator_deactivate_req_fn *elevator_deactivate_req_fn;
 
@@ -126,6 +130,7 @@ extern void elv_merged_request(struct request_queue *, struct request *, int);
 extern void elv_bio_merged(struct request_queue *q, struct request *,
 				struct bio *);
 extern void elv_requeue_request(struct request_queue *, struct request *);
+extern int elv_reinsert_request(struct request_queue *, struct request *);
 extern struct request *elv_former_request(struct request_queue *, struct request *);
 extern struct request *elv_latter_request(struct request_queue *, struct request *);
 extern int elv_register_queue(struct request_queue *q);
-- 
1.7.6

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