Re: [dpdk-dev] [PATCH] vhost: Fix wrong handling of virtqueue array index

["Xie, Huawei" <huawei.xie@intel.com>]

On 10/27/2015 3:52 PM, Tetsuya Mukawa wrote:
> The patch fixes wrong handling of virtqueue array index when
> GET_VRING_BASE message comes.
> The vhost backend will receive the message per virtqueue.
> Also we should call a destroy callback handler when both RXQ
> and TXQ receives the message.
>
> Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
> ---
>  lib/librte_vhost/vhost_user/virtio-net-user.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/lib/librte_vhost/vhost_user/virtio-net-user.c b/lib/librte_vhost/vhost_user/virtio-net-user.c
> index a998ad8..99c075f 100644
> --- a/lib/librte_vhost/vhost_user/virtio-net-user.c
> +++ b/lib/librte_vhost/vhost_user/virtio-net-user.c
> @@ -283,12 +283,10 @@ user_get_vring_base(struct vhost_device_ctx ctx,
>  	struct vhost_vring_state *state)
>  {
>  	struct virtio_net *dev = get_device(ctx);
> +	uint16_t base_idx = state->index / VIRTIO_QNUM * VIRTIO_QNUM;
>  
>  	if (dev == NULL)
>  		return -1;
> -	/* We have to stop the queue (virtio) if it is running. */
> -	if (dev->flags & VIRTIO_DEV_RUNNING)
> -		notify_ops->destroy_device(dev);
Hi Tetsuya:
I don't understand why we move it to the end of the function.
If we don't tell the application to remove the virtio device from the
data plane, then the vhost application is still operating on that
device, we shouldn't do anything to the virtio_net device.
For this case, as vhost doesn't use kickfd, it will not cause issue, but
i think it is best practice firstly to remove it from data plan through
destroy_device.

I think we could call destroy_device the first time we receive this
message. Currently we don't have per queue granularity control to only
remove one queue from data plane.

I am Okay to only close the kickfd for the specified queue index.

Btw, do you meet issue with previous implementation?
>  
>  	/* Here we are safe to get the last used index */
>  	ops->get_vring_base(ctx, state->index, state);
> @@ -300,15 +298,17 @@ user_get_vring_base(struct vhost_device_ctx ctx,
>  	 * sent and only sent in vhost_vring_stop.
>  	 * TODO: cleanup the vring, it isn't usable since here.
>  	 */
> -	if (dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd >= 0) {
> -		close(dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd);
> -		dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd = -1;
> -	}
> -	if (dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd >= 0) {
> -		close(dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd);
> -		dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd = -1;
> +	if (dev->virtqueue[state->index]->kickfd >= 0) {
> +		close(dev->virtqueue[state->index]->kickfd);
> +		dev->virtqueue[state->index]->kickfd = -1;
>  	}
>  
> +	/* We have to stop the queue (virtio) if it is running. */
> +	if ((dev->flags & VIRTIO_DEV_RUNNING) &&
> +			(dev->virtqueue[base_idx + VIRTIO_RXQ]->kickfd == -1) &&
> +			(dev->virtqueue[base_idx + VIRTIO_TXQ]->kickfd == -1))
> +		notify_ops->destroy_device(dev);
> +
>  	return 0;
>  }
>