dm: inherit QUEUE_FLAG_SG_GAPS flags from underlying queues

A DM device must inherit the QUEUE_FLAG_SG_GAPS flags from its
underlying block devices' request queues.

This fixes problems when submitting cloned requests to multipathed
devices requiring virtually contiguous buffers.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-table.c

@@ -1389,6 +1389,14 @@ static int queue_supports_sg_merge(struct dm_target *ti, struct dm_dev *dev,
 	return q && !test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
 }
 
+static int queue_supports_sg_gaps(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_SG_GAPS, &q->queue_flags);
+}
+
 static bool dm_table_all_devices_attribute(struct dm_table *t,
 					   iterate_devices_callout_fn func)
 {
@@ -1509,6 +1517,11 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	else
 		queue_flag_set_unlocked(QUEUE_FLAG_NO_SG_MERGE, q);
 
+	if (dm_table_all_devices_attribute(t, queue_supports_sg_gaps))
+		queue_flag_clear_unlocked(QUEUE_FLAG_SG_GAPS, q);
+	else
+		queue_flag_set_unlocked(QUEUE_FLAG_SG_GAPS, q);
+
 	dm_table_set_integrity(t);
 
 	/*