[dpdk-dev] [PATCH] virtio: Fix enqueue/dequeue can't handle chained vring descriptors.

[Xie, Huawei]

On 5/4/2015 2:27 PM, Ouyang Changchun wrote:
> Vring enqueue need consider the 2 cases:
>  1. Vring descriptors chained together, the first one is for virtio header, the rest are for real data;
>  2. Only one descriptor, virtio header and real data share one single descriptor;
>
> So does vring dequeue.
>
> Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
> ---
>  lib/librte_vhost/vhost_rxtx.c | 60 +++++++++++++++++++++++++++++++------------
>  1 file changed, 44 insertions(+), 16 deletions(-)
>
> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> index 510ffe8..3135883 100644
> --- a/lib/librte_vhost/vhost_rxtx.c
> +++ b/lib/librte_vhost/vhost_rxtx.c
> @@ -59,7 +59,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>  	struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
>  	uint64_t buff_addr = 0;
>  	uint64_t buff_hdr_addr = 0;
> -	uint32_t head[MAX_PKT_BURST], packet_len = 0;
> +	uint32_t head[MAX_PKT_BURST];
>  	uint32_t head_idx, packet_success = 0;
>  	uint16_t avail_idx, res_cur_idx;
>  	uint16_t res_base_idx, res_end_idx;
> @@ -113,6 +113,10 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>  	rte_prefetch0(&vq->desc[head[packet_success]]);
>  
>  	while (res_cur_idx != res_end_idx) {
> +		uint32_t offset = 0;
> +		uint32_t data_len, len_to_cpy;
> +		uint8_t plus_hdr = 0;
> +
>  		/* Get descriptor from available ring */
>  		desc = &vq->desc[head[packet_success]];
>  
> @@ -125,7 +129,6 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>  
>  		/* Copy virtio_hdr to packet and increment buffer address */
>  		buff_hdr_addr = buff_addr;
> -		packet_len = rte_pktmbuf_data_len(buff) + vq->vhost_hlen;
>  
>  		/*
>  		 * If the descriptors are chained the header and data are
> @@ -136,24 +139,44 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>  			desc = &vq->desc[desc->next];
>  			/* Buffer address translation. */
>  			buff_addr = gpa_to_vva(dev, desc->addr);
> -			desc->len = rte_pktmbuf_data_len(buff);
>  		} else {
>  			buff_addr += vq->vhost_hlen;
> -			desc->len = packet_len;
> +			plus_hdr = 1;
>  		}
>  
> +		data_len = rte_pktmbuf_data_len(buff);
> +		len_to_cpy = RTE_MIN(data_len, desc->len);
> +		do {
> +			if (len_to_cpy > 0) {
> +				/* Copy mbuf data to buffer */
> +				rte_memcpy((void *)(uintptr_t)buff_addr,
> +					(const void *)(rte_pktmbuf_mtod(buff, const char *) + offset),
> +					len_to_cpy);
> +				PRINT_PACKET(dev, (uintptr_t)buff_addr,
> +					len_to_cpy, 0);
> +
> +				desc->len = len_to_cpy + (plus_hdr ? vq->vhost_hlen : 0);

Do we really need to rewrite the desc->len again and again?  At least we
only have the possibility to change the value of desc->len of the last
descriptor.

> +				offset += len_to_cpy;
> +				if (desc->flags & VRING_DESC_F_NEXT) {
> +					desc = &vq->desc[desc->next];
> +					buff_addr = gpa_to_vva(dev, desc->addr);
> +					len_to_cpy = RTE_MIN(data_len - offset, desc->len);
> +				} else
> +					break;

Still there are two issues here.
a) If the data couldn't be fully copied to chain of guest buffers, we
shouldn't do any copy.
b) scatter mbuf isn't considered.

> +			} else {
> +				desc->len = 0;
> +				if (desc->flags & VRING_DESC_F_NEXT)
> +                                        desc = &vq->desc[desc->next];
> +				else
> +					break;
> +			}
> +		} while (1);
> +
>  		/* Update used ring with desc information */
>  		vq->used->ring[res_cur_idx & (vq->size - 1)].id =
>  							head[packet_success];
> -		vq->used->ring[res_cur_idx & (vq->size - 1)].len = packet_len;
> -
> -		/* Copy mbuf data to buffer */
> -		/* FIXME for sg mbuf and the case that desc couldn't hold the mbuf data */
> -		rte_memcpy((void *)(uintptr_t)buff_addr,
> -			rte_pktmbuf_mtod(buff, const void *),
> -			rte_pktmbuf_data_len(buff));
> -		PRINT_PACKET(dev, (uintptr_t)buff_addr,
> -			rte_pktmbuf_data_len(buff), 0);
> +		vq->used->ring[res_cur_idx & (vq->size - 1)].len =
> +							offset + vq->vhost_hlen;
>  
>  		res_cur_idx++;
>  		packet_success++;
> @@ -583,7 +606,14 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
>  		desc = &vq->desc[head[entry_success]];
>  
>  		/* Discard first buffer as it is the virtio header */
> -		desc = &vq->desc[desc->next];
> +		if (desc->flags & VRING_DESC_F_NEXT) {
> +			desc = &vq->desc[desc->next];
> +			vb_offset = 0;
> +			vb_avail = desc->len;
> +		} else {
> +			vb_offset = vq->vhost_hlen;
> +			vb_avail = desc->len - vb_offset;
> +		}
>  
>  		/* Buffer address translation. */
>  		vb_addr = gpa_to_vva(dev, desc->addr);
> @@ -602,8 +632,6 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
>  		vq->used->ring[used_idx].id = head[entry_success];
>  		vq->used->ring[used_idx].len = 0;
>  
> -		vb_offset = 0;
> -		vb_avail = desc->len;
>  		/* Allocate an mbuf and populate the structure. */
>  		m = rte_pktmbuf_alloc(mbuf_pool);
>  		if (unlikely(m == NULL)) {