Currently, in zerocopy mode with mergeable receive buffer, virtio-net
does not support multi buffer but a single buffer only. This commit adds
support for multi mergeable receive buffer in the zerocopy XDP path by
utilizing XDP buffer with frags.

Signed-off-by: Bui Quang Minh <redacted>
---
  drivers/net/virtio_net.c | 123 +++++++++++++++++++++------------------
  1 file changed, 66 insertions(+), 57 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e53ba600605a..a9558650f205 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -45,6 +45,8 @@ module_param(napi_tx, bool, 0644);
  #define VIRTIO_XDP_TX		BIT(0)
  #define VIRTIO_XDP_REDIR	BIT(1)
  
+#define VIRTNET_MAX_ZC_SEGS	8
+
  /* RX packet size EWMA. The average packet size is used to determine the packet
   * buffer size when refilling RX rings. As the entire RX ring may be refilled
   * at once, the weight is chosen so that the EWMA will be insensitive to short-

@@ -1232,65 +1234,53 @@ static void xsk_drop_follow_bufs(struct net_device *dev,
  	}
  }
  
-static int xsk_append_merge_buffer(struct virtnet_info *vi,
-				   struct receive_queue *rq,
-				   struct sk_buff *head_skb,
-				   u32 num_buf,
-				   struct virtio_net_hdr_mrg_rxbuf *hdr,
-				   struct virtnet_rq_stats *stats)
+static int virtnet_build_xsk_buff_mrg(struct virtnet_info *vi,
+				      struct receive_queue *rq,
+				      u32 num_buf,
+				      struct xdp_buff *xdp,
+				      struct virtnet_rq_stats *stats)
  {
-	struct sk_buff *curr_skb;
-	struct xdp_buff *xdp;
-	u32 len, truesize;
-	struct page *page;
+	unsigned int len;
  	void *buf;
  
-	curr_skb = head_skb;
+	if (num_buf < 2)
+		return 0;
+
+	while (num_buf > 1) {
+		struct xdp_buff *new_xdp;
  
-	while (--num_buf) {
  		buf = virtqueue_get_buf(rq->vq, &len);
-		if (unlikely(!buf)) {
-			pr_debug("%s: rx error: %d buffers out of %d missing\n",
-				 vi->dev->name, num_buf,
-				 virtio16_to_cpu(vi->vdev,
-						 hdr->num_buffers));
+		if (!unlikely(buf)) {