Re: [PATCH 1/5] null_blk: remove the bio based I/O path

[Keith Busch <kbusch@kernel.org>]

On Wed, Feb 14, 2024 at 10:54:57AM +0100, Christoph Hellwig wrote:
> @@ -2036,11 +1813,15 @@ static int null_validate_conf(struct nullb_device *dev)
>  		pr_err("legacy IO path is no longer available\n");
>  		return -EINVAL;
>  	}
> +	if (dev->queue_mode == NULL_Q_BIO) {
> +		pr_err("BIO-based IO path is no longer available, using blk-mq instead.\n");
> +		dev->queue_mode = NULL_Q_MQ;
> +	}

Seems pointless to keep dev->queue_mode around if only one value is
valid.

Instead of checking the param here once per device, could we do it just
once for the module in null_set_queue_mode()?

---
@@ -134,7 +134,7 @@ static int null_param_store_val(const char *str, int *val, int min, int max)

 static int null_set_queue_mode(const char *str, const struct kernel_param *kp)
 {
-	return null_param_store_val(str, &g_queue_mode, NULL_Q_BIO, NULL_Q_MQ);
+	return null_param_store_val(str, &g_queue_mode, NULL_Q_MQ, NULL_Q_MQ);
 }

 static const struct kernel_param_ops null_queue_mode_param_ops = {
--