block: avoid polling configuration errors

This patch adds a poll queue check, aiming to help users use polled IO
accurately.

If users do polled IO but the device doesn't have poll queues, they will
get suboptimal performance data and waste CPU resources. Add a poll queue
check batching this. If users don't have the device properly configured,
or if it simply doesn't support polled IO, it will error the IO with
-EOPNOTSUPP. This is similar to what we used to do for sync polled IO,
which is no longer supported.

Signed-off-by: hexue <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: xue01-he

block/blk-core.c

@@ -791,8 +791,11 @@ void submit_bio_noacct(struct bio *bio)
 		}
 	}
 
-	if (!(q->limits.features & BLK_FEAT_POLL))
+	if (!(q->limits.features & BLK_FEAT_POLL) &&
+			(bio->bi_opf & REQ_POLLED)) {
 		bio_clear_polled(bio);
+		goto not_supported;
+	}
 
 	switch (bio_op(bio)) {
 	case REQ_OP_READ: