virtio_net: introduce virtnet_build_skb()

This logic is used in multiple places, now we separate it into
a helper.
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

@@ -443,6 +443,22 @@ static unsigned int mergeable_ctx_to_truesize(void *mrg_ctx)
 	return (unsigned long)mrg_ctx & ((1 << MRG_CTX_HEADER_SHIFT) - 1);
 }
 
+static struct sk_buff *virtnet_build_skb(void *buf, unsigned int buflen,
+					 unsigned int headroom,
+					 unsigned int len)
+{
+	struct sk_buff *skb;
+
+	skb = build_skb(buf, buflen);
+	if (unlikely(!skb))
+		return NULL;
+
+	skb_reserve(skb, headroom);
+	skb_put(skb, len);
+
+	return skb;
+}
+
 /* Called from bottom half context */
 static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 				   struct receive_queue *rq,
@@ -476,13 +492,10 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 
 	/* copy small packet so we can reuse these pages */
 	if (!NET_IP_ALIGN && len > GOOD_COPY_LEN && tailroom >= shinfo_size) {
-		skb = build_skb(buf, truesize);
+		skb = virtnet_build_skb(buf, truesize, p - buf, len);
 		if (unlikely(!skb))
 			return NULL;
 
-		skb_reserve(skb, p - buf);
-		skb_put(skb, len);
-
 		page = (struct page *)page->private;
 		if (page)
 			give_pages(rq, page);
@@ -946,13 +959,10 @@ static struct sk_buff *receive_small_build_skb(struct virtnet_info *vi,
 	buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
 		SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
-	skb = build_skb(buf, buflen);
-	if (!skb)
+	skb = virtnet_build_skb(buf, buflen, headroom, len);
+	if (unlikely(!skb))
 		return NULL;
 
-	skb_reserve(skb, headroom);
-	skb_put(skb, len);
-
 	buf += header_offset;
 	memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
 
@@ -1028,12 +1038,10 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 		goto err_xdp;
 	}
 
-	skb = build_skb(buf, buflen);
-	if (!skb)
+	skb = virtnet_build_skb(buf, buflen, xdp.data - buf, len);
+	if (unlikely(!skb))
 		goto err;
 
-	skb_reserve(skb, xdp.data - buf);
-	skb_put(skb, len);
 	if (metasize)
 		skb_metadata_set(skb, metasize);