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>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c9306e3403fe28c61f17e0d5983002ee3e9fbfaf..a99bea4554529bc2c00f5a6f642687715625d490 100644 (file)
--- 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,