Re: [Qemu-devel] [PATCH 04/18] virtio: Return error from virtqueue_next_desc

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Apr 17, 2015 at 03:59:19PM +0800, Fam Zheng wrote:
> Two callers pass error_abort now, which can be changed to check return value
> and pass the error on.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  hw/virtio/virtio.c | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index a525f8e..2a24829 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -329,10 +329,11 @@ static int virtqueue_get_head(VirtQueue *vq, unsigned int idx,
>      return head;
>  }
>  
> -static unsigned virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa,
> -                                    unsigned int i, unsigned int max)
> +static int virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa,
> +                               unsigned int i, unsigned int max,
> +                               Error **errp)
>  {
> -    unsigned int next;
> +    int next;
>  
>      /* If this descriptor says it doesn't chain, we're done. */
>      if (!(vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_NEXT)) {
> @@ -345,8 +346,8 @@ static unsigned virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa,
>      smp_wmb();
>  
>      if (next >= max) {
> -        error_report("Desc next is %u", next);
> -        exit(1);
> +        error_setg(errp, "Desc next is %u", next);
> +        return -EINVAL;

I think it's best to return max here. No need to change return type
then.

>      }
>  
>      return next;
> @@ -392,7 +393,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
>              num_bufs = i = 0;
>          }
>  
> -        do {
> +        while (true) {
>              /* If we've got too many, that implies a descriptor loop. */
>              if (++num_bufs > max) {
>                  error_report("Looped descriptor");
> @@ -407,7 +408,11 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
>              if (in_total >= max_in_bytes && out_total >= max_out_bytes) {
>                  goto done;
>              }
> -        } while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max);
> +            i = virtqueue_next_desc(vdev, desc_pa, i, max, &error_abort);
> +            if (i == max) {
> +                break;
> +            }
> +        }
>  
>          if (!indirect)
>              total_bufs = num_bufs;
> @@ -493,7 +498,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
>      }
>  
>      /* Collect all the descriptors */
> -    do {
> +    while (true) {
>          struct iovec *sg;
>  
>          if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE) {
> @@ -519,7 +524,11 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
>              error_report("Looped descriptor");
>              exit(1);
>          }
> -    } while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max);
> +        i = virtqueue_next_desc(vdev, desc_pa, i, max, &error_abort);
> +        if (i == max) {
> +            break;
> +        }
> +    }
>  

Why refactor this as part of this patch?

>      /* Now map what we have collected */
>      virtqueue_map_sg(elem->in_sg, elem->in_addr, elem->in_num, 1,
> -- 
> 1.9.3