Re: [Qemu-devel] [PATCH 1/3] virtio: introduce virtqueue_unmap_sg()

[Andrew James <andrew.james@hpe.com>]

On 09/18/2015 02:01 AM, Jason Wang wrote:
> Factor out sg unmapping logic. This will be reused by the patch that
> can discard descriptor.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/virtio/virtio.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 0832db9..eb8d5ca 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -243,15 +243,12 @@ int virtio_queue_empty(VirtQueue *vq)
>      return vring_avail_idx(vq) == vq->last_avail_idx;
>  }
>  
> -void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
> -                    unsigned int len, unsigned int idx)
> +static void virtqueue_unmap_sg(VirtQueue *vq, const VirtQueueElement *elem,
> +                               unsigned int len)
>  {
>      unsigned int offset;
>      int i;
>  
> -    trace_virtqueue_fill(vq, elem, len, idx);
> -
> -    offset = 0;
>      for (i = 0; i < elem->in_num; i++) {
>          size_t size = MIN(len - offset, elem->in_sg[i].iov_len);
>  

Should the "offset = 0" really be dropped here? Seems like it ends
up uninitialized. GCC thinks it might too.

> @@ -266,6 +263,14 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
>          cpu_physical_memory_unmap(elem->out_sg[i].iov_base,
>                                    elem->out_sg[i].iov_len,
>                                    0, elem->out_sg[i].iov_len);
> +}
> +
> +void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
> +                    unsigned int len, unsigned int idx)
> +{
> +    trace_virtqueue_fill(vq, elem, len, idx);
> +
> +    virtqueue_unmap_sg(vq, elem, len);
>  
>      idx = (idx + vring_used_idx(vq)) % vq->vring.num;
>  
> 

Thanks,
-- 
Andrew James