[dpdk-dev] [PATCH v7 3/8] vhost: vring queue setup for multiple queue support

[Xie, Huawei]

On 10/21/2015 11:48 AM, Yuanhan Liu wrote:
> All queue pairs, including the default (the first) queue pair,
> are allocated dynamically, when a vring_call message is received
> first time for a specific queue pair.
>
> This is a refactor work for enabling vhost-user multiple queue;
> it should not break anything as it does no functional changes:
> we don't support mq set, so there is only one mq at max.
>
> This patch is based on Changchun's patch.
>
[...]
>  
>  void
> @@ -290,13 +298,9 @@ 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[VIRTIO_RXQ]->kickfd) >= 0) {
> -		close(dev->virtqueue[VIRTIO_RXQ]->kickfd);
> -		dev->virtqueue[VIRTIO_RXQ]->kickfd = -1;
> -	}
> -	if ((dev->virtqueue[VIRTIO_TXQ]->kickfd) >= 0) {
> -		close(dev->virtqueue[VIRTIO_TXQ]->kickfd);
> -		dev->virtqueue[VIRTIO_TXQ]->kickfd = -1;
> +	if ((dev->virtqueue[state->index]->kickfd) >= 0) {
> +		close(dev->virtqueue[state->index]->kickfd);
> +		dev->virtqueue[state->index]->kickfd = -1;
>  	}
Since we change the behavior here, better list in the commit message as
well.

>  
>  
> @@ -680,13 +704,21 @@ set_vring_call(struct vhost_device_ctx ctx, struct vhost_vring_file *file)
>  {
>  	struct virtio_net *dev;
>  	struct vhost_virtqueue *vq;
> +	uint32_t cur_qp_idx = file->index / VIRTIO_QNUM;
>  
>  	dev = get_device(ctx);
>  	if (dev == NULL)
>  		return -1;
>  
> +	/* alloc vring queue pair if it is a new queue pair */
> +	if (cur_qp_idx + 1 > dev->virt_qp_nb) {
> +		if (alloc_vring_queue_pair(dev, cur_qp_idx) < 0)
> +			return -1;
> +	}
> +
Here we rely on the fact that this set_vring_call message is sent in the
continuous ascending order of queue idx 0, 1, 2, ...

>  	/* file->index refers to the queue index. The txq is 1, rxq is 0. */
>  	vq = dev->virtqueue[file->index];
> +	assert(vq != NULL);
>  
If we allocate the queue until the we receive the first vring message,
better add comment that we rely on this fact.
Could we add the vhost-user message to tell us the queue number QEMU
allocates before vring message?
>  	if (vq->callfd >= 0)
>  		close(vq->callfd);