virtio_net: introduce receive_small_build_xdp

Simplifying receive_small() function. Bringing the logic relating to
build_skb together.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -931,6 +931,34 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
 	return NULL;
 }
 
+static struct sk_buff *receive_small_build_skb(struct virtnet_info *vi,
+					       unsigned int xdp_headroom,
+					       void *buf,
+					       unsigned int len)
+{
+	unsigned int header_offset;
+	unsigned int headroom;
+	unsigned int buflen;
+	struct sk_buff *skb;
+
+	header_offset = VIRTNET_RX_PAD + xdp_headroom;
+	headroom = vi->hdr_len + header_offset;
+	buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
+		SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
+	skb = build_skb(buf, buflen);
+	if (!skb)
+		return NULL;
+
+	skb_reserve(skb, headroom);
+	skb_put(skb, len);
+
+	buf += header_offset;
+	memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
+
+	return skb;
+}
+
 static struct sk_buff *receive_small_xdp(struct net_device *dev,
 					 struct virtnet_info *vi,
 					 struct receive_queue *rq,
@@ -1030,9 +1058,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
 {
 	unsigned int xdp_headroom = (unsigned long)ctx;
 	struct page *page = virt_to_head_page(buf);
-	unsigned int header_offset;
-	unsigned int headroom;
-	unsigned int buflen;
 	struct sk_buff *skb;
 
 	len -= vi->hdr_len;
@@ -1060,20 +1085,9 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		rcu_read_unlock();
 	}
 
-	header_offset = VIRTNET_RX_PAD + xdp_headroom;
-	headroom = vi->hdr_len + header_offset;
-	buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
-		SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
-
-	skb = build_skb(buf, buflen);
-	if (!skb)
-		goto err;
-	skb_reserve(skb, headroom);
-	skb_put(skb, len);
-
-	buf += header_offset;
-	memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
-	return skb;
+	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
+	if (likely(skb))
+		return skb;
 
 err:
 	stats->drops++;