[PATCH v2 2/2] md: enable io polling

[Andrzej Jakowski <andrzej.jakowski@xxxxxxxxxxxxxxx>]

From: Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx>

Provide a callback for polling the mddev which in turn polls the active
member devices in non-spinning manner. Enable it only if all members
support polling.

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@xxxxxxxxx>
Signed-off-by: Andrzej Jakowski <andrzej.jakowski@xxxxxxxxxxxxxxx>
---
 drivers/md/md.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 469f551863be..849d22a2108f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5564,6 +5564,28 @@ int mddev_init_writes_pending(struct mddev *mddev)
 }
 EXPORT_SYMBOL_GPL(mddev_init_writes_pending);
 
+static int md_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
+{
+	struct mddev *mddev = q->queuedata;
+	struct md_rdev *rdev;
+	int ret = 0;
+	int rv;
+
+	rdev_for_each(rdev, mddev) {
+		if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))
+			continue;
+
+		rv = blk_poll(bdev_get_queue(rdev->bdev), cookie, false);
+		if (rv < 0) {
+			ret = rv;
+			break;
+		}
+		ret += rv;
+	}
+
+	return ret;
+}
+
 static int md_alloc(dev_t dev, char *name)
 {
 	/*
@@ -5628,6 +5650,7 @@ static int md_alloc(dev_t dev, char *name)
 
 	blk_queue_make_request(mddev->queue, md_make_request);
 	blk_set_stacking_limits(&mddev->queue->limits);
+	mddev->queue->poll_fn = md_poll;
 
 	disk = alloc_disk(1 << shift);
 	if (!disk) {
@@ -5932,12 +5955,17 @@ int md_run(struct mddev *mddev)
 
 	if (mddev->queue) {
 		bool nonrot = true;
+		bool poll = true;
 
 		rdev_for_each(rdev, mddev) {
-			if (rdev->raid_disk >= 0 &&
-			    !blk_queue_nonrot(bdev_get_queue(rdev->bdev))) {
-				nonrot = false;
-				break;
+			if (rdev->raid_disk >= 0) {
+				struct request_queue *q;
+
+				q = bdev_get_queue(rdev->bdev);
+				if (!blk_queue_nonrot(q))
+					nonrot = false;
+				if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
+					poll = false;
 			}
 		}
 		if (mddev->degraded)
@@ -5946,6 +5974,10 @@ int md_run(struct mddev *mddev)
 			blk_queue_flag_set(QUEUE_FLAG_NONROT, mddev->queue);
 		else
 			blk_queue_flag_clear(QUEUE_FLAG_NONROT, mddev->queue);
+		if (poll)
+			blk_queue_flag_set(QUEUE_FLAG_POLL, mddev->queue);
+		else
+			blk_queue_flag_clear(QUEUE_FLAG_POLL, mddev->queue);
 		mddev->queue->backing_dev_info->congested_data = mddev;
 		mddev->queue->backing_dev_info->congested_fn = md_congested;
 	}
-- 
2.20.1