Re: [dpdk-dev] [PATCH] vhost: fix external backends readiness

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Wednesday, September 23, 2020 5:49 PM
> To: dev@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; matan@mellanox.com;
> Zawadzki, Tomasz <tomasz.zawadzki@intel.com>; Liu, Changpeng
> <changpeng.liu@intel.com>
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [PATCH] vhost: fix external backends readiness
> 
> Commit d0fcc38f5fa4 ("vhost: improve device readiness notifications")
> makes the assumption that every Virtio devices are considered
> ready for preocessing as soon as first queue pair is configured
> and enabled.
> 
> While this is true for Virtio-net, it isn't for Virtio-scsi
> and Virtio-blk.
> 
> This patch fixes this by only making this assumption for
> the builtin Virtio-net backend, and restores back to previous
> behaviour for other backends.
> 
> Fixes: d0fcc38f5fa4 ("vhost: improve device readiness notifications")
> 
> Reported-by: Changpeng Liu <changpeng.liu@intel.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
> ---
>  lib/librte_vhost/vhost_user.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 501218e192..b00e1f91dc 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1343,21 +1343,28 @@ vq_is_ready(struct virtio_net *dev, struct
> vhost_virtqueue *vq)
>  	       vq->enabled;
>  }
> 
> -#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 2u
> +#define VIRTIO_BUILTIN_NUM_VQS_TO_BE_READY 2u
> 
>  static int
>  virtio_is_ready(struct virtio_net *dev)
>  {
>  	struct vhost_virtqueue *vq;
> -	uint32_t i;
> +	uint32_t i, nr_vring = dev->nr_vring;
> 
>  	if (dev->flags & VIRTIO_DEV_READY)
>  		return 1;
> 
> -	if (dev->nr_vring < VIRTIO_DEV_NUM_VQS_TO_BE_READY)
> +	if (!dev->nr_vring)
>  		return 0;
> 
> -	for (i = 0; i < VIRTIO_DEV_NUM_VQS_TO_BE_READY; i++) {
> +	if (dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET) {
> +		nr_vring = VIRTIO_BUILTIN_NUM_VQS_TO_BE_READY;
> +
> +		if (dev->nr_vring < nr_vring)
> +			return 0;
> +	}
> +
> +	for (i = 0; i < nr_vring; i++) {
>  		vq = dev->virtqueue[i];
> 
>  		if (!vq_is_ready(dev, vq))
> --
> 2.26.2

Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>