linux-kernel - Re: [PATCH] vhost: silence an unused-variable warning

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Date:   Thu, 7 Mar 2019 11:00:19 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost: silence an unused-variable warning


On 2019/3/6 下午7:05, Arnd Bergmann wrote:
> On some architectures, the MMU can be disabled, leading to access_ok()
> becoming an empty macro that does not evaluate its size argument,
> which in turn produces an unused-variable warning:
>
> drivers/vhost/vhost.c:1191:9: error: unused variable 's' [-Werror,-Wunused-variable]
>          size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
>
> Mark the variable as __maybe_unused to shut up that warning.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/vhost/vhost.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index a2e5dc7716e2..5ace833de746 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1188,7 +1188,7 @@ static bool vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
>   			 struct vring_used __user *used)
>   
>   {
> -	size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> +	size_t s __maybe_unused = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
>   
>   	return access_ok(desc, num * sizeof *desc) &&
>   	       access_ok(avail,


Acked-by: Jason Wang <jasowang@...hat.com>