[for-4.16 PATCH v2 1/5] block: establish request failover callback

[Mike Snitzer <snitzer@redhat.com>]

All requests allocated from a request_queue with this callback set can
failover their requests during completion.

This callback is expected to use the blk_steal_bios() interface to
transfer a request's bios back to an upper-layer bio-based
request_queue.

This will be used by both NVMe multipath and DM multipath.  Without it
DM multipath cannot get access to NVMe-specific error handling that NVMe
core provides in nvme_complete_rq().

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 include/linux/blkdev.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8089ca17db9a..f45f5925e100 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -278,6 +278,7 @@ typedef int (lld_busy_fn) (struct request_queue *q);
 typedef int (bsg_job_fn) (struct bsg_job *);
 typedef int (init_rq_fn)(struct request_queue *, struct request *, gfp_t);
 typedef void (exit_rq_fn)(struct request_queue *, struct request *);
+typedef void (failover_rq_fn)(struct request *);
 
 enum blk_eh_timer_return {
 	BLK_EH_NOT_HANDLED,
@@ -423,6 +424,11 @@ struct request_queue {
 	exit_rq_fn		*exit_rq_fn;
 	/* Called from inside blk_get_request() */
 	void (*initialize_rq_fn)(struct request *rq);
+	/*
+	 * Callback to failover request's bios back to upper layer
+	 * bio-based request_queue using blk_steal_bios().
+	 */
+	failover_rq_fn		*failover_rq_fn;
 
 	const struct blk_mq_ops	*mq_ops;
 
-- 
2.15.0