Re: [Qemu-devel] [RFC 6/7] virtio: handle virtqueue_num_heads() errors

[Fam Zheng <famz@redhat.com>]

On Thu, 03/24 17:56, Stefan Hajnoczi wrote:
> If the index avail ring index is bogus virtqueue_num_heads() must return

s/index avail/avail/ ?

> -EINVAL.
> 
> The only caller is virtqueue_get_avail_bytes().  Return saying no bytes
> are available when virtqueue_num_heads() fails.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/virtio/virtio.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index f845df2..525af8b 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -320,9 +320,9 @@ static int virtqueue_num_heads(VirtQueue *vq, unsigned int idx)
>  
>      /* Check it isn't doing very strange things with descriptor numbers. */
>      if (num_heads > vq->vring.num) {
> -        error_report("Guest moved used index from %u to %u",
> +        virtio_error(vq->vdev, "Guest moved used index from %u to %u",
>                       idx, vq->shadow_avail_idx);
> -        exit(1);
> +        return -EINVAL;
>      }
>      /* On success, callers read a descriptor at vq->last_avail_idx.
>       * Make sure descriptor read does not bypass avail index read. */
> @@ -390,7 +390,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
>      idx = vq->last_avail_idx;
>  
>      total_bufs = in_total = out_total = 0;
> -    while (virtqueue_num_heads(vq, idx)) {
> +    while ((rc = virtqueue_num_heads(vq, idx)) > 0) {
>          VirtIODevice *vdev = vq->vdev;
>          unsigned int max, num_bufs, indirect = 0;
>          VRingDesc desc;
> @@ -451,6 +451,11 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
>          else
>              total_bufs++;
>      }
> +
> +    if (rc < 0) {
> +        goto err;
> +    }
> +
>  done:
>      if (in_bytes) {
>          *in_bytes = in_total;
> -- 
> 2.5.5
>