Re: [PATCH net-next v2 2/7] virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx

[Jason Wang <jasowang@redhat.com>]

On 2021/1/16 上午10:59, Xuan Zhuo wrote:
> If support xsk, a new ptr will be recovered during the
> process of freeing the old ptr. In order to distinguish between ctx sent
> by XDP_TX and ctx sent by xsk, a struct is added here to distinguish
> between these two situations. virtnet_xdp_type.type It is used to
> distinguish different ctx, and virtnet_xdp_type.offset is used to record
> the offset between "true ctx" and virtnet_xdp_type.
>
> The newly added virtnet_xsk_hdr will be used for xsk.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>


Any reason that you can't simply encode the type in the pointer itself 
as we used to do?

#define VIRTIO_XSK_FLAG    BIT(1)

?


> ---
>   drivers/net/virtio_net.c | 75 ++++++++++++++++++++++++++++++++++++++----------
>   1 file changed, 60 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ba8e637..e707c31 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -94,6 +94,22 @@ struct virtnet_rq_stats {
>   	u64 kicks;
>   };
>   
> +enum {
> +	XDP_TYPE_XSK,
> +	XDP_TYPE_TX,
> +};
> +
> +struct virtnet_xdp_type {
> +	int offset:24;
> +	unsigned type:8;
> +};
> +
> +struct virtnet_xsk_hdr {
> +	struct virtnet_xdp_type type;
> +	struct virtio_net_hdr_mrg_rxbuf hdr;
> +	u32 len;
> +};
> +
>   #define VIRTNET_SQ_STAT(m)	offsetof(struct virtnet_sq_stats, m)
>   #define VIRTNET_RQ_STAT(m)	offsetof(struct virtnet_rq_stats, m)
>   
> @@ -251,14 +267,19 @@ static bool is_xdp_frame(void *ptr)
>   	return (unsigned long)ptr & VIRTIO_XDP_FLAG;
>   }
>   
> -static void *xdp_to_ptr(struct xdp_frame *ptr)
> +static void *xdp_to_ptr(struct virtnet_xdp_type *ptr)
>   {
>   	return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
>   }
>   
> -static struct xdp_frame *ptr_to_xdp(void *ptr)
> +static struct virtnet_xdp_type *ptr_to_xtype(void *ptr)
> +{
> +	return (struct virtnet_xdp_type *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> +}
> +
> +static void *xtype_get_ptr(struct virtnet_xdp_type *xdptype)
>   {
> -	return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> +	return (char *)xdptype + xdptype->offset;
>   }
>   
>   /* Converting between virtqueue no. and kernel tx/rx queue no.
> @@ -459,11 +480,16 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   				   struct xdp_frame *xdpf)
>   {
>   	struct virtio_net_hdr_mrg_rxbuf *hdr;
> +	struct virtnet_xdp_type *xdptype;
>   	int err;
>   
> -	if (unlikely(xdpf->headroom < vi->hdr_len))
> +	if (unlikely(xdpf->headroom < vi->hdr_len + sizeof(*xdptype)))
>   		return -EOVERFLOW;
>   
> +	xdptype = (struct virtnet_xdp_type *)(xdpf + 1);
> +	xdptype->offset = (char *)xdpf - (char *)xdptype;
> +	xdptype->type = XDP_TYPE_TX;
> +
>   	/* Make room for virtqueue hdr (also change xdpf->headroom?) */
>   	xdpf->data -= vi->hdr_len;
>   	/* Zero header and leave csum up to XDP layers */
> @@ -473,7 +499,7 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   
>   	sg_init_one(sq->sg, xdpf->data, xdpf->len);
>   
> -	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
> +	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdptype),
>   				   GFP_ATOMIC);
>   	if (unlikely(err))
>   		return -ENOSPC; /* Caller handle free/refcnt */
> @@ -523,8 +549,11 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	/* Free up any pending old buffers before queueing new ones. */
>   	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>   		if (likely(is_xdp_frame(ptr))) {
> -			struct xdp_frame *frame = ptr_to_xdp(ptr);
> +			struct virtnet_xdp_type *xtype;
> +			struct xdp_frame *frame;
>   
> +			xtype = ptr_to_xtype(ptr);
> +			frame = xtype_get_ptr(xtype);
>   			bytes += frame->len;
>   			xdp_return_frame(frame);
>   		} else {
> @@ -1373,24 +1402,34 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>   
>   static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
>   {
> -	unsigned int len;
>   	unsigned int packets = 0;
>   	unsigned int bytes = 0;
> -	void *ptr;
> +	unsigned int len;
> +	struct virtnet_xdp_type *xtype;
> +	struct xdp_frame        *frame;
> +	struct virtnet_xsk_hdr  *xskhdr;
> +	struct sk_buff          *skb;
> +	void                    *ptr;
>   
>   	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>   		if (likely(!is_xdp_frame(ptr))) {
> -			struct sk_buff *skb = ptr;
> +			skb = ptr;
>   
>   			pr_debug("Sent skb %p\n", skb);
>   
>   			bytes += skb->len;
>   			napi_consume_skb(skb, in_napi);
>   		} else {
> -			struct xdp_frame *frame = ptr_to_xdp(ptr);
> +			xtype = ptr_to_xtype(ptr);
>   
> -			bytes += frame->len;
> -			xdp_return_frame(frame);
> +			if (xtype->type == XDP_TYPE_XSK) {
> +				xskhdr = (struct virtnet_xsk_hdr *)xtype;
> +				bytes += xskhdr->len;
> +			} else {
> +				frame = xtype_get_ptr(xtype);
> +				xdp_return_frame(frame);
> +				bytes += frame->len;
> +			}
>   		}
>   		packets++;
>   	}
> @@ -2659,10 +2698,16 @@ static void free_unused_bufs(struct virtnet_info *vi)
>   	for (i = 0; i < vi->max_queue_pairs; i++) {
>   		struct virtqueue *vq = vi->sq[i].vq;
>   		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> -			if (!is_xdp_frame(buf))
> +			if (!is_xdp_frame(buf)) {
>   				dev_kfree_skb(buf);
> -			else
> -				xdp_return_frame(ptr_to_xdp(buf));
> +			} else {
> +				struct virtnet_xdp_type *xtype;
> +
> +				xtype = ptr_to_xtype(buf);
> +
> +				if (xtype->type != XDP_TYPE_XSK)
> +					xdp_return_frame(xtype_get_ptr(xtype));
> +			}
>   		}
>   	}
>