Re: [dm-devel] [PATCH v3 09/11] dm: support IO polling for bio-based dm device

On 2/19/21 10:17 PM, Mikulas Patocka wrote:

On Mon, 8 Feb 2021, Jeffle Xu wrote:

quoted

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c2945c90745e..8423f1347bb8 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c

@@ -1657,6 +1657,68 @@ static blk_qc_t dm_submit_bio(struct bio *bio)
 	return BLK_QC_T_NONE;
 }
 
+static int dm_poll_one_md(struct mapped_device *md);
+
+static int dm_poll_one_dev(struct dm_target *ti, struct dm_dev *dev,
+				sector_t start, sector_t len, void *data)
+{
+	int i, *count = data;
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+	struct blk_mq_hw_ctx *hctx;
+
+	if (queue_is_mq(q)) {
+		if (!percpu_ref_tryget(&q->q_usage_counter))
+			return 0;
+
+		queue_for_each_poll_hw_ctx(q, hctx, i)
+			*count += blk_mq_poll_hctx(q, hctx);
+
+		percpu_ref_put(&q->q_usage_counter);
+	} else
+		*count += dm_poll_one_md(dev->bdev->bd_disk->private_data);

This is fragile, because in the future there may be other bio-based 
drivers that support polling. You should check that "q" is really a device 
mapper device before calling dm_poll_one_md on it.

Sorry I missed this reply. Your advice matters, thanks.

-- 
Thanks,
Jeffle