[PATCH RFC 7/7] dm: add support for IO polling

[Jeffle Xu <jefflexu@linux.alibaba.com>]

Enable iopoll when all underlying target devices supports iopoll.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 drivers/md/dm-table.c | 28 ++++++++++++++++++++++++++++
 drivers/md/dm.c       |  1 +
 2 files changed, 29 insertions(+)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 188f41287f18..b0cd5bf58c3c 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1791,6 +1791,31 @@ static bool dm_table_requires_stable_pages(struct dm_table *t)
 	return false;
 }
 
+static int device_supports_poll(struct dm_target *ti, struct dm_dev *dev,
+				sector_t start, sector_t len, void *data)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+
+	return q && test_bit(QUEUE_FLAG_POLL, &q->queue_flags);
+}
+
+static bool dm_table_supports_poll(struct dm_table *t)
+{
+	struct dm_target *ti;
+	unsigned int i;
+
+	/* Ensure that all targets support iopoll. */
+	for (i = 0; i < dm_table_get_num_targets(t); i++) {
+		ti = dm_table_get_target(t, i);
+
+		if (!ti->type->iterate_devices ||
+		    !ti->type->iterate_devices(ti, device_supports_poll, NULL))
+			return false;
+	}
+
+	return true;
+}
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			       struct queue_limits *limits)
 {
@@ -1883,6 +1908,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 #endif
 
 	blk_queue_update_readahead(q);
+
+	if (dm_table_supports_poll(t))
+		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
 }
 
 unsigned int dm_table_get_num_targets(struct dm_table *t)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 03c2b867acaa..ffd2c5ead256 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -3049,6 +3049,7 @@ static const struct pr_ops dm_pr_ops = {
 };
 
 static const struct block_device_operations dm_blk_dops = {
+	.iopoll = blk_bio_poll,
 	.submit_bio = dm_submit_bio,
 	.open = dm_blk_open,
 	.release = dm_blk_close,
-- 
2.27.0