[PATCH] null_blk: Always split BIOs to respect queue limits

[Damien Le Moal <dlemoal@kernel.org>]

The function null_submit_bio() used for null_blk devices configured
with a BIO-based queue never splits BIOs according to the queue limits
set with the various module and configfs parameters that the user can
specify.

Add a call to bio_split_to_limits() to correctly handle large
BIOs that need splitting. Doing so also fixes issues with zoned devices
as a large BIO may cross over a zone boundary, which breaks null_blk
zone emulation.

While at it, remove all the local variable that are not necessary.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 drivers/block/null_blk/main.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 36755f263e8e..514c2592046a 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1528,12 +1528,16 @@ static struct nullb_queue *nullb_to_queue(struct nullb *nullb)
 
 static void null_submit_bio(struct bio *bio)
 {
-	sector_t sector = bio->bi_iter.bi_sector;
-	sector_t nr_sectors = bio_sectors(bio);
-	struct nullb *nullb = bio->bi_bdev->bd_disk->private_data;
-	struct nullb_queue *nq = nullb_to_queue(nullb);
+	struct nullb_queue *nq =
+		nullb_to_queue(bio->bi_bdev->bd_disk->private_data);
+
+	/* Respect the queue limits */
+	bio = bio_split_to_limits(bio);
+	if (!bio)
+		return;
 
-	null_handle_cmd(alloc_cmd(nq, bio), sector, nr_sectors, bio_op(bio));
+	null_handle_cmd(alloc_cmd(nq, bio), bio->bi_iter.bi_sector,
+			bio_sectors(bio), bio_op(bio));
 }
 
 #ifdef CONFIG_BLK_DEV_NULL_BLK_FAULT_INJECTION
-- 
2.43.0