From: Christoph Hellwig <hch@lst.de>
Date: Thu, 2 Nov 2017 21:29:51 +0300
Subject: [PATCH] block: add a blk_steal_bios helper
Git-commit: ef71de8b15d891b27b8c983a9a8972b11cb4576a
Patch-Mainline: v4.15-rc1
References: FATE#323952, FATE#322506

This helpers allows to bounce steal the uncompleted bios from a request so
that they can be reissued on another path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-core.c       | 21 +++++++++++++++++++++
 include/linux/blkdev.h |  2 ++
 2 files changed, 23 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index b73e1a8..b727afc 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2724,6 +2724,27 @@ struct request *blk_fetch_request(struct request_queue *q)
 }
 EXPORT_SYMBOL(blk_fetch_request);
 
+/*
+ * Steal bios from a request and add them to a bio list.
+ * The request must not have been partially completed before.
+ */
+void blk_steal_bios(struct bio_list *list, struct request *rq)
+{
+	if (rq->bio) {
+		if (list->tail)
+			list->tail->bi_next = rq->bio;
+		else
+			list->head = rq->bio;
+		list->tail = rq->biotail;
+
+		rq->bio = NULL;
+		rq->biotail = NULL;
+	}
+
+	rq->__data_len = 0;
+}
+EXPORT_SYMBOL_GPL(blk_steal_bios);
+
 /**
  * blk_update_request - Special helper function for request stacking drivers
  * @req:      the request being processed
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7ae3b3e..bc80157 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1107,6 +1107,8 @@ static inline unsigned int blk_rq_count_bios(struct request *rq)
 extern void blk_start_request(struct request *rq);
 extern struct request *blk_fetch_request(struct request_queue *q);
 
+void blk_steal_bios(struct bio_list *list, struct request *rq);
+
 /*
  * Request completion related functions.
  *
-- 
1.8.5.6