[PATCH 4/7] block: add a blk_steal_bios helper

[Christoph Hellwig]

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 at lst.de>
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
Reviewed-by: Hannes Reinecke <hare at suse.com>
---
 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 b8c80f39f5fe..54fe673fb3ba 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2767,6 +2767,27 @@ 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 780f01db5899..45c63764a14e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1110,6 +1110,8 @@ extern struct request *blk_peek_request(struct request_queue *q);
 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.
  *
-- 
2.14.2