Linux Virtualization - Mar 2019 - [PATCH] vhost: silence an unused-variable warning

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 at arndb.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,
-- 
2.20.0

On 2019/3/6 ??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 at arndb.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 at redhat.com>