Re: [Qemu-devel] [PATCH 1/2] hw/virtio/virtio: Don't allow guests to add/remove queues

[Michael S. Tsirkin]

On Thu, Jul 25, 2013 at 02:37:42PM +0100, Peter Maydell wrote:
> A queue size of 0 is used to indicate a nonexistent queue, so
> don't allow the guest to flip a queue between zero-size and
> non-zero-size. Don't permit setting of negative queue sizes
> either.
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  hw/virtio/virtio.c |   10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 09f62c6..d5b0502 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -673,10 +673,14 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
>  
>  void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
>  {
> -    if (num <= VIRTQUEUE_MAX_SIZE) {
> -        vdev->vq[n].vring.num = num;
> -        virtqueue_init(&vdev->vq[n]);
> +    if ((num == 0 && vdev->vq[n].vring.num != 0) ||
> +        (num != 0 && vdev->vq[n].vring.num == 0) ||

Cleaner (imho)

    !num != !vdev->vq[n].vring.num


> +        (num > VIRTQUEUE_MAX_SIZE) ||

Pls don't put () around simple math.
It has natural precedence wrt <> so it just makes it
look like lisp.

> +        (num < 0)) {

How does it ever get negative?
assert (num >= 0) instead?

> +        return;
>      }
> +    vdev->vq[n].vring.num = num;
> +    virtqueue_init(&vdev->vq[n]);
>  }
>  
>  int virtio_queue_get_num(VirtIODevice *vdev, int n)
> -- 
> 1.7.9.5