blk-mq: handle dma_drain_size

Make blk-mq handle the dma_drain_size field the same way as the old request
path.

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

1 files changed, 10 insertions, 0 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c9306e3403fe..a99bea455452 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -582,6 +582,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
                 list_del_init(&rq->queuelist);
                 blk_mq_start_request(rq);
 
+                if (q->dma_drain_size && blk_rq_bytes(rq)) {
+                        /*
+                         * make sure space for the drain appears we
+                         * know we can do this because max_hw_segments
+                         * has been adjusted to be one fewer than the
+                         * device can handle
+                         */
+                        rq->nr_phys_segments++;
+                }
+
                 /*
                  * Last request in the series. Flag it as such, this
                  * enables drivers to know when IO should be kicked off,