blk-mq: make ->flush_rq fully transparent to drivers

Drivers shouldn't have to care about the block layer setting aside a
request to implement the flush state machine.  We already override the
mq context and tag to make it more transparent, but so far haven't deal
with the driver private data in the request.  Make sure to override this
as well, and while we're at it add a proper helper sitting in blk-mq.c
that implements the full impersonation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 2 insertions, 10 deletions

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 0e42adcfb55e..c41fc19f75d1 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -307,16 +307,8 @@ static bool blk_kick_flush(struct request_queue *q)
         q->flush_pending_idx ^= 1;
 
         blk_rq_init(q, q->flush_rq);
-        if (q->mq_ops) {
-                /*
-                 * Reuse the tag value from the fist waiting request,
-                 * with blk-mq the tag is generated during request
-                 * allocation and drivers can rely on it being inside
-                 * the range they asked for.
-                 */
-                q->flush_rq->mq_ctx = first_rq->mq_ctx;
-                q->flush_rq->tag = first_rq->tag;
-        }
+        if (q->mq_ops)
+                blk_mq_clone_flush_request(q->flush_rq, first_rq);
 
         q->flush_rq->cmd_type = REQ_TYPE_FS;
         q->flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;