nvme: don't set io_opt if NOWS is zero

NOWS is one of the annoying "0's based values" in NVMe, where 0 means one
and we thus can't detect if it isn't set.  Thus a NOWS value of 0 means
that the Namespace Optimal Write Size is a single LBA, which is clearly
bogus.  Ignore the value in that case and don't propagate an io_opt
value to the block layer.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Chaitanya Kulkarni <[email protected]>
Reviewed-by: Sagi Grimberg <[email protected]>
Reviewed-by: Nitesh Shetty <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Christoph Hellwig

drivers/nvme/host/core.c

@@ -2024,7 +2024,8 @@ static bool nvme_update_disk_info(struct nvme_ns *ns, struct nvme_id_ns *id,
 		/* NPWG = Namespace Preferred Write Granularity */
 		phys_bs = bs * (1 + le16_to_cpu(id->npwg));
 		/* NOWS = Namespace Optimal Write Size */
-		io_opt = bs * (1 + le16_to_cpu(id->nows));
+		if (id->nows)
+			io_opt = bs * (1 + le16_to_cpu(id->nows));
 	}
 
 	/*